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1. Angular and radial sampling criteria for monostatic and bistatic radar tomography of solar system small bodies

Author: Wlodek Kofman, Yonggyu Gim, Mark S. Haynes, Alain Herique, and Ines Fenni
Subjects: Physics, Atmospheric Science, Acoustics, Scalar (physics), Aerospace Engineering, Sampling (statistics), Astronomy and Astrophysics, Ephemeris, law.invention, Bistatic radar, Geophysics, Space and Planetary Science, law, General Earth and Planetary Sciences, Coherence (signal processing), Monochromatic color, Radar, Point target
Abstract: Low-frequency radar tomography is an important subsurface imaging method for future planetary missions to solar system small bodies. We derive angular and radial sampling criteria for monostatic and bistatic radar tomography algorithms that are based on monochromatic free-space backprojection and spherical apertures. We use the vector Born approximation to highlight the degeneracy of monochromatic bistatic source/receiver direction pair measurements in k-space. Analytical expressions are then derived for the scalar point target response of different spherical sampling geometries. We also derive the angular sampling step and total number of sampling points required to fully reconstruct the point target response for monostatic, bistatic, and non-degenerate k-space spherical apertures. These are evaluated for object sizes and radar operating frequencies expected in small body tomography. We also analyze and derive expressions for the coherence loss of spherical apertures due to random errors in a sensor’s radial position, which provides requirements on the a posteriori ephemeris knowledge. Finally, we derive a vector backprojection algorithm suitable for focusing quad-pol scattering matrix (S-matrix) data that is tested using full-wave S-matrix simulations of dielectric point targets. This work is intended to aid radar instrument performance analysis and inform the design and architecture of future instruments and missions.
Published: 2021
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2. Electromagnetic full waveform inversion based on quadratic Wasserstein metric

Author: Jian Deng, Peimin Zhu, Wlodek Kofman, Jinpeng Jiang, Yuefeng Yuan, and Alain Herique
Subjects: Physics, Electrical and Electronic Engineering
Abstract: Electromagnetic full waveform inversion (FWI) is a high-resolution method to reveal the distribution of dielectric parameters of the medium. Traditionally, the electromagnetic FWI is usually performed using the L-2 norm misfit function, which suffers severely local minimum problems since the L-2 norm misfit function is nonconvex in the model space. To mitigate the local minimum problem, the quadratic Wasserstein metric (W-2) derived from the optimal transport theory is proposed to replace the L-2 norm to define the misfit function. Since the computation of the W-2 metric requires the signal to be mass conservation and nonnegativity, the softplus function is applied to rescale the signal to meet these two requirements. Based on the softplus scaling method, a hierarchy inversion strategy that involves multiple scaling coefficients is proposed to mitigate the local minimum problem without sacrificing the inversion resolution. The numerical experiments prove that the FWI based on W-2 (W-2-FWI) is more independent on the initial model than the FWI based on the L-2 norm (L-2-FWI), and the W-2-FWI could be more robust to zero-mean random noise than the L-2-FWI. Finally, a comprehensive numerical experiment related to asteroid radar tomography is carried out to show the potential of W-2-FWI in realistic applications.
Published: 2022

3. Post-rendezvous radar properties of comet 67P/CG from the Rosetta Mission: understanding future Earth-based radar observations and the dynamical evolution of comets

Author: Essam Heggy, M. Ramy El-Maarry, Alain Herique, Wlodek Kofman, and Elizabeth M. Palmer
Subjects: Physics, 010504 meteorology & atmospheric sciences, Comet, Rendezvous, Astronomy and Astrophysics, 01 natural sciences, Astrobiology, law.invention, Radar observations, Space and Planetary Science, law, 0103 physical sciences, Radar, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract: Radar observations provide crucial insights into the formation and dynamical evolution of comets. This ability is constrained by our knowledge of the dielectric and textural properties of these small-bodies. Using several observations by Rosetta as well as results from the Earth-based Arecibo radio telescope, we provide an updated and comprehensive dielectric and roughness description of Comet 67P/CG, which can provide new constraints on the radar properties of other nuclei. Furthermore, contrary to previous assumptions of cometary surfaces being dielectrically homogeneous and smooth, we find that cometary surfaces are dielectrically heterogeneous ( εr′≈1.6–3.2), and are rough at X- and S-band frequencies, which are widely used in characterization of small-bodies. We also investigate the lack of signal broadening in CONSERT observations through the comet head. Our results suggest that primordial building blocks in the subsurface are either absent, smaller than the radar wavelength, or have a weak dielectric contrast (Δ εr′). To constrain this ambiguity, we use optical albedo measurements by the OSIRIS camera of the freshly exposed subsurface after the Aswan cliff collapse. We find that the hypothetical subsurface blocks should have |Δ εr′|≳0.15, setting an upper limit of ∼ 1 m on the size of 67P/CG's primordial building blocks if they exist. Our analysis is consistent with a purely thermal origin for the ∼ 3 m surface bumps on pit walls and cliff-faces, hypothesized to be high-centred polygons formed from fracturing of the sintered shallow ice-bearing subsurface due to seasonal thermal expansion and contraction. Potential changes in 67P/CG's radar reflectivity at these at X- and S-bands can be associated with large-scale structural changes of the nucleus rather than small-scale textural ones. Monitoring changes in 67P/CG's radar properties during repeated close-approaches via Earth-based observations can constrain the dynamical evolution of its cometary nucleus.
Published: 2019
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4. Low Frequency Radar (LFR) on the JUVENTAS CubeSat for HERA / ESA mission

Author: Hannah Goldberg, Alain Herique, Dirk Plettemeier, Wlodek Kofman, and Yves Rogez
Subjects: Physics, CubeSat, HERA, Low-frequency radar, Remote sensing
Abstract: The Low Frequency Radar (LFR) on the JUVENTAS CubeSat for HERA / ESA mission to Didymos Binary Asteroid is a unique opportunity to perform direct measurements of its internal structure and regolith. LFR has been developed to fathom asteroid from a small platform. This instrument is inherited from CONSERT/Rosetta and has been redesigned in the frame of the AIDA and HERA ESA mission.Onboard JUVENTAS, LFR is operating in monostatic mode to probe down to the first hundreds of meters into the subsurface and to achieve a full tomography of the Didymos' moonlet. Direct observations of the internal structure of asteroids can solve still open basic questions like: Is the body a monolithic piece of rock or a rubble-pile? How high is the porosity? What is the typical size of the constituent blocks? Are these blocks homogeneous or heterogeneous? How is the regolith covering its surface constituted?The low frequency aboard the Juventas CubeSat will contribute to the solution of these open and for planetary defense crucial questions.- The first LRF objective is the characterization of the moonlet interior, to identify internal structure and to analyze the size distribution and heterogeneity of constitutive blocks from sub metric to global- The second objective is the estimation of average permittivity and mapping of its spatial variation especially in the crater area.- The same characterization applied to the main of the binary system is among secondary objectives.- Supporting shape modeling and determination of the dynamical state by radar ranging is a further secondary objective.This paper will present the instrument concept and measurement strategy, its performances and the expected science return.
Published: 2020
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5. Towards Asteroid Tomography: Modellings and Measurements Using an Analogue Model

Author: Liisa-Ida Sorsa, Sampsa Pursiainen, J.-M. Geffrin, Christelle Eyraud, Wlodek Kofman, Alain Herique, Institut FRESNEL (FRESNEL), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), Tampere University of Applied Sciences [Finland], Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales [Toulouse] (CNES)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France -Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France, Space Research Centre [Torun], Polska Akademia Nauk = Polish Academy of Sciences (PAN), Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)
Subjects: Electromagnetic field, Physics, Solar System, Tomographic reconstruction, 020208 electrical & electronic engineering, 020206 networking & telecommunications, 02 engineering and technology, Inverse problem, Computational physics, [SPI.ELEC]Engineering Sciences [physics]/Electromagnetism, Microwave imaging, Asteroid, Frequency domain, 0202 electrical engineering, electronic engineering, information engineering, Astrophysics::Earth and Planetary Astrophysics, Focus (optics), ComputingMilieux_MISCELLANEOUS
Abstract: The interior structures of the comets and asteroids, still poorly known, might hold a unique key to understand the early Solar System. Considering the interaction of an illuminated electromagnetic wave with this kind of targets, these ”objects” are very large compared to the applicable wavelength. Consequently, tomographic imaging of such targets, i.e., reconstructing their interior structure via multiple measurements, constitutes a challenging inverse problem. To reach this objective and to develop and test inverse algorithms, we need to investigate electromagnetic fields that have interacted with structures analogous to real asteroids and comets. In this study, we focus on the acquisition of these fields considering three methods: calculated fields obtained with (1) time and (2) frequency domain methods and (3) microwave measurements performed for an analogue model, i.e., a small-scale asteroid model.
Published: 2020
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6. CONSERT constrains the internal structure of 67P at a few metres size scale

Author: Pierre Pasquero, Christophe Guiffaut, Valérie Ciarletti, Jérémie Lasue, Anny Chantal Levasseur-Regourd, Florentin Lemmonier, Alain Herique, Wlodek Kofman, Dirk Plettemeier, IMPEC - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), Institut de recherche en astrophysique et planétologie (IRAP), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Technische Universität Dresden (TUD), Systèmes RF (XLIM-SRF), XLIM (XLIM), Université de Limoges (UNILIM)-Centre National de la Recherche Scientifique (CNRS)-Université de Limoges (UNILIM)-Centre National de la Recherche Scientifique (CNRS), PLANETO - LATMOS, Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Technische Universität Dresden = Dresden University of Technology (TU Dresden), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), and Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Solar System, Planetesimal, 010504 meteorology & atmospheric sciences, Comet, 67P/Churyumov–Gerasimenko, 01 natural sciences, law.invention, law, Planet, 0103 physical sciences, medicine, comets, Radar, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, Nebula, scattering, Astronomy, Astronomy and Astrophysics, Wavelength, medicine.anatomical_structure, [SDU]Sciences of the Universe [physics], Space and Planetary Science, numerical simulation, Astrophysics::Earth and Planetary Astrophysics, Nucleus, radar
Abstract: International audience; The internal properties of cometary nuclei are the best clues to the size distribution and properties of the early planetesimals that formed the planets during the early solar system nebula processes. The CONSERT radar was designed to probe the interior of comet 67P/Churyumov-Gerasimenko with a wavelength of about 3 meters. It was successfully operated during the First Science Sequence of the Rosetta mission when the CONSERT’s wave propagated through part of the nucleus’ small lobe. The shape of the received signals provides some hints about the internal structure of the comet's small lobe. The limited broadening observed on the received pulses is compared to simulations performed on a series of non-homogeneous nucleus models to put constrains on the potential structures at the wavelength's scale. The study allows to exclude structures showing a permittivity contrast larger than 0.25 inside the sounded part of the nucleus at a few-metre size scale.
Published: 2017
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7. Oversampled Pulse Compression Based on Signal Modeling: Application to CONSERT/Rosetta Radar

Author: Oudomsack Pierre Pasquero, Wlodek Kofman, and Alain Herique
Subjects: Physics, Clock rate, 0211 other engineering and technologies, Context (language use), 02 engineering and technology, 01 natural sciences, law.invention, Transmission (telecommunications), Pulse compression, Aliasing, law, 0103 physical sciences, General Earth and Planetary Sciences, Nyquist frequency, Electrical and Electronic Engineering, Radar, 010303 astronomy & astrophysics, Algorithm, Multipath propagation, 021101 geological & geomatics engineering, Remote sensing
Abstract: The context of space missions implies very strong constraints on the design of the instruments. For instance, mass, data rates, power consumption, clock frequency, and accuracy are very limited. These limitations degrade the performance and the accuracy of the measurements. This paper is related to the study of signals sampled at a low frequency. More exactly, we propose an oversampled pulse compression method for radar signals, which allows to reconstruction the signals with a much higher sampling rate. Consequently, this method allows significantly improving the multipath amplitude and the delay estimation accuracy. The efficiency of our method is clearly demonstrated with real measurements. These latter correspond to calibration measurements performed on ground with the radar COmets Nucleus Sounding Experiment by Radio-wave Transmission. The latter allows performing the tomography in the transmission of 67P Churyumov–Gerasimenko comets nucleus in the frame of the Rosetta/European Space Agency space mission. The results show that the proposed method allows estimating the delays with accuracy better than 10% of the sampling period in the case of a sampling frequency value close to the Nyquist limit. The analysis of the measured signals shows how a small frequency aliasing power degrades the delay estimation performance. This problem can be resolved using an estimation method based on an end-to-end signal modeling.
Published: 2017
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8. The interior of Comet 67P/C-G; revisiting CONSERT results with the exact position of the Philae lander

Author: Sonia Zine, Alain Herique, Yves Rogez, Wlodek Kofman, Anny Chantal Levasseur-Regourd, Laurent Jorda, Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales [Toulouse] (CNES)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA), Space Research Centre of Polish Academy of Sciences (CBK), Polska Akademia Nauk = Polish Academy of Sciences (PAN), Laboratoire d'Astrophysique de Marseille (LAM), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Centre National d'Études Spatiales [Toulouse] (CNES), PLANETO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Sorbonne Université (SU)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France -Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France, Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Physics, 67P/Churyumov-Gerasimenko, 010504 meteorology & atmospheric sciences, Comet, Astronomy, radar astronomy -comets, Astronomy and Astrophysics, 67P/Churyumov–Gerasimenko, Radar astronomy, 01 natural sciences, general -comets, 13. Climate action, Space and Planetary Science, Position (vector), [SDU]Sciences of the Universe [physics], 0103 physical sciences, Comets, individual, techniques, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract: CONSERT, a bistatic radar onboard the Rosetta spacecraft and its Philae lander, was designed to probe the nucleus of comet 67P/Churyumov–Gerasimenko with radio waves at 90 MHz frequency. In 2016 September, the exact position of Philae was retrieved, within the region previously identified by CONSERT. This allowed us to revisit the measurements and improve our analysis of the properties of the interior, the results of which we present here. The relative permittivity of the materials is found to range from about 1.7 to 1.95 in the shallow subsurface (
Published: 2020
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9. Ionospheric composition measurement by EISCAT using a global fit procedure

Author: B. Cabrit, Wlodek Kofman, and EGU, Publication
Subjects: Physics, Atmospheric Science, [SDU.OCEAN] Sciences of the Universe [physics]/Ocean, Atmosphere, Probleme inverse, lcsh:QC801-809, Geology, Astronomy and Astrophysics, Composition (combinatorics), Inverse problem, F region, lcsh:QC1-999, Computational physics, Ion, lcsh:Geophysics. Cosmic physics, Altitude, Space and Planetary Science, QUIET, [SDU.STU] Sciences of the Universe [physics]/Earth Sciences, Earth and Planetary Sciences (miscellaneous), lcsh:Q, Ionosphere, lcsh:Science, lcsh:Physics, Remote sensing
Abstract: The aim of this paper is to show the gain of the global fit procedure compared to the classical gate-by-gate analysis in the simultaneous determination of the temperatures and composition profiles in the lower F region. A method for the evaluation of the transition altitude and the width of the transition region between molecular and atomic ions is described in the case of the EISCAT CP1 experiment; it is validated using a simulated experiment. It is shown that alternating-code gates have to be processed together with the long-pulse gates. Our new method is applied on six days of actual data. The results obtained during quiet periods are compared with independent estimations.
Published: 2018

10. Imaging the inner structure of a comet from few measurements in a bistatic scenario: case of a scale model

Author: J.-M. Geffrin, Alain Herique, Wlodek Kofman, Christelle Eyraud, HIPE (HIPE), Institut FRESNEL (FRESNEL), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU), and Eyraud, Christelle
Subjects: Physics, Bistatic radar, [SPI.ELEC]Engineering Sciences [physics]/Electromagnetism, [SPI.ELEC] Engineering Sciences [physics]/Electromagnetism, Comet, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], [SDU.ASTR.EP] Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Astronomy, Scale model, ComputingMilieux_MISCELLANEOUS
Abstract: International audience
Published: 2018

11. Imaging the interior of a comet from bistatic microwave measurements: case of a scale comet model

Author: Jean-Michel Geffrin, Alain Herique, Wlodek Kofman, Christelle Eyraud, HIPE (HIPE), Institut FRESNEL (FRESNEL), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), and Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])
Subjects: Atmospheric Science, 010504 meteorology & atmospheric sciences, Anechoic chamber, Comet, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Aerospace Engineering, Microwave measurements, 01 natural sciences, Imaging, Electromagnetic wave, 0103 physical sciences, Comet analog, Internal structure, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Remote sensing, Physics, Astronomy and Astrophysics, Reconstruction algorithm, Polarization (waves), Bistatic radar, [SPI.ELEC]Engineering Sciences [physics]/Electromagnetism, Geophysics, Space and Planetary Science, Asteroid, Radar Tomography, General Earth and Planetary Sciences, Bistatic configuration, Scale model, Microwave
Abstract: Link to the publisher version: https://www.sciencedirect.com/science/article/pii/S0273117717307330; International audience; Imaging the internal structure of comets and asteroids is an important way to provide information about their formation process. In this paper, we investigate the possibility to image the interior of such structures with electromagnetic wave in the microwave domain (radar system) using an inverse algorithm adapted to take advantage of a bistatic configuration, taking into account the polarization effects, and which presents low memory requirement. To this end, a scale model of a comet/asteroid was built and was used for an experimental simulation. The scattered fields of this scale model were measured in a perfectly controlled environment, in an anechoic chamber, to avoid measurement disturbances and to focus this study only on which structural information can be obtained with such measurements. To profit from the spatial diversity of information, a vectorial-induced current reconstruction algorithm was used. Two configurations were tested and analyzed including one with very few measurements. From the qualitative reconstructed maps, we have shown that it is possible to detect the presence of a core in both cases.
Published: 2018
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12. Homogeneity of 67P/Churyumov-Gerasimenko as seen by CONSERT: implication on composition and formation

Author: Wlodek Kofman, Sonia Zine, Valérie Ciarletti, Alain Herique, Jürgen Blum, Jean-Baptiste Vincent, Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Space Research Centre of Polish Academy of Sciences (CBK), Polska Akademia Nauk = Polish Academy of Sciences (PAN), Institut für Geophysik und Extraterrestrische Physik [Braunschweig] (IGEP), Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig], DLR Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt [Berlin] (DLR), PLANETO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Sorbonne Université (SU)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), Polska Akademia Nauk (PAN), Technische Universität Braunschweig [Braunschweig], IMPEC - LATMOS, and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)
Subjects: 67P/Churyumov-Gerasimenko, Physics, Permittivity, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 010504 meteorology & atmospheric sciences, Characteristic length, Homogeneity (statistics), Mineralogy, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, comet, Radar astronomy, Space and Planetary Science, 0103 physical sciences, Gravitational collapse, radar astronomy, Porosity, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract: Context. After the landing of Philae, CONSERT probed the nucleus of 67P/Churyumov-Gerasimenko (67P) and observed no heterogeneities at metric scale within the probed part of the small lobe of 67P. Further studies have then quantified the observed homogeneity in terms of maximum permittivity contrast versus the typical size of heterogeneities. Aims. The aim of this article is to interpret the sensitivity limits of CONSERT measurements in terms of composition, and to provide constraints on the maximum variability in composition, porosity, and local dust-to-ice ratio. Methods. The sensitivity of CONSERT measurements to local variations in density, dust-to-ice ratio, and composition was analyzed using permittivity modeling of mixtures. Results. We interpret the maximum detectable heterogeneity size and contrast in terms of composition and porosity of the nucleus. The sensitivity to porosity is ±10 percent points for heterogeneities with a characteristic length scale of a few meters; the sensitivity to local variations in the composition is limited. Conclusions. In terms of accretion, our results are compatible only with scenarios generating porosity heterogeneities at scales lower than one meter, or with porosity variations smaller than ±10 percent points. This is clearly compatible with an accretion model of a gentle gravitational collapse of a pebble cloud.
Published: 2019
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13. Radar properties of comets: Parametric dielectric modeling of Comet 67P/Churyumov–Gerasimenko

Author: Wlodek Kofman, Kevin Righter, Stephen M. Clifford, Essam Heggy, Alain Herique, and Elizabeth M. Palmer
Subjects: Physics, Comet, Astronomy, Astronomy and Astrophysics, Dielectric, Mass ratio, Computational physics, law.invention, Wavelength, medicine.anatomical_structure, Space and Planetary Science, law, Comet nucleus, medicine, Radar, Porosity, Nucleus
Abstract: In 2014, the European Space Agency’s Rosetta mission is scheduled to rendezvous with Comet 67P/Churyumov–Gerasimenko (Comet 67P). Rosetta’s CONSERT experiment aims to explore the cometary nucleus’ geophysical properties using radar tomography. The expected scientific return and inversion algorithms are mainly dependent on our understanding of the dielectric properties of the comet nucleus and how they vary with the spatial distribution of geophysical parameters. Using observations of Comets 9P/Tempel 1 and 81P/Wild 2 in combination with dielectric laboratory measurements of temperature, porosity, and dust-to-ice mass ratio dependencies for cometary analog material, we have constructed two hypothetical three-dimensional parametric dielectric models of Comet 67P’s nucleus to assess different dielectric scenarios of the inner structure. Our models suggest that dust-to-ice mass ratios and porosity variations generate the most significant measurable dielectric contrast inside the comet nucleus, making it possible to explore the structural and compositional hypotheses of cometary nuclei. Surface dielectric variations, resulting from temperature changes induced by solar illumination of the comet’s faces, have also been modeled and suggest that the real part of the dielectric constant varies from 1.9 to 3.0, hence changing the surface radar reflectivity. For CONSERT, this variation could be significant at low incidence angles, when the signal propagates through a length of dust mantle comparable to the wavelength. The overall modeled dielectric permittivity spatial and temporal variations are therefore consistent with the expected deep penetration of CONSERT’s transmitted wave through the nucleus. It is also clear that changes in the physical properties of the nucleus induce sufficient variation in the dielectric properties of cometary material to allow their inversion from radar tomography.
Published: 2012
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14. Rosetta rendezvous and CONSERT operations in 2014: A chimeric surface model of 67P/Churyumov Gerasimenko

Author: Alain Herique, Sonia Zine, Wlodek Kofman, Yves Rogez, and Jérémie Lasue
Subjects: Surface (mathematics), Physics, Comet, Rendezvous, Astronomy and Astrophysics, computer.software_genre, law.invention, Simulation software, Depth sounding, Orbiter, Space and Planetary Science, law, Comet nucleus, Radar, computer, Remote sensing
Abstract: In 2014 the European Space Agency's Rosetta probe will rendezvous with the comet 67P/Churyumov Gerasimenko (67P) and the Philae Lander will land on the surface of the nucleus. Following the landing, the COmet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) radar will perform the tomography of the nucleus by measuring radiowave propagation through the comet between the Lander and the orbiter. Preparation for these operations, in particular the development and validation of simulation software, requires a shape model of the surface of 67P. The complexity of this model should reflect the environmental conditions that will be found in 2014. In this paper, we show that existing models of 67P are not of a sufficiently high resolution to constitute interesting test cases. Following a review of current shape models for other comets, we propose a composite which is a hybrid of the 67P and 81P/Wild 2 models.
Published: 2012
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15. A porosity gradient in 67P/C-G nucleus suggested from CONSERT and SESAME-PP results: an interpretation based on new laboratory permittivity measurements of porous icy analogues

Author: Pierre Sabouroux, Yann Brouet, A. Le Gall, Antoine Pommerol, Cyril Szopa, Wlodek Kofman, Luisa Neves, Nicolas Thomas, Nathalie Carrasco, Olivier Poch, P. Encrenaz, Valérie Ciarletti, Alain Herique, Anny Chantal Levasseur-Regourd, A. Lethuillier, Physikalisches Institut [Bern], Universität Bern [Bern], PLANETO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), HIPE (HIPE), Institut FRESNEL (FRESNEL), Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU), Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique (LERMA), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université de Cergy Pontoise (UCP), Université Paris-Seine-Université Paris-Seine-Centre National de la Recherche Scientifique (CNRS), Space Research Centre of Polish Academy of Sciences (CBK), Polska Akademia Nauk = Polish Academy of Sciences (PAN), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), ESTER - LATMOS, Institut Universitaire de France (IUF), Ministère de l'Education nationale, de l’Enseignement supérieur et de la Recherche (M.E.N.E.S.R.), Swiss National Science Foundation, Centre National d'Etudes Spatiales (CNES), IMPEC - LATMOS, Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Paris (ENS Paris)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université de Cergy Pontoise (UCP), Polska Akademia Nauk (PAN), Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), Universität Bern [Bern] (UNIBE), and École normale supérieure - Paris (ENS-PSL)
Subjects: Permittivity, 67P/Churyumov-Gerasimenko, 010504 meteorology & atmospheric sciences, 530 Physics, Comet, data analysis, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Mineralogy, Astrophysics, 01 natural sciences, Interpretation (model theory), 0103 physical sciences, medicine, Porosity, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, Range (particle radiation), Spacecraft, business.industry, 520 Astronomy, Astronomy and Astrophysics, Tholin, 620 Engineering, medicine.anatomical_structure, 13. Climate action, Space and Planetary Science, business, Nucleus, radar
Abstract: International audience; The Rosetta spacecraft made a rendezvous with comet 67P/Churyumov-Gerasimenko (67P) in August 2014, soon after the Philae module landed on the small lobe of the nucleus on 12 November 2014. The CONSERT instrument, onboard Rosetta and Philae, sounded the upper part of the interior of 67P with radiowaves at 90 MHz and determined an average of the real part of the permittivity (hereafter ϵ′) equal to about 1.27. The SESAME-PP instrument, onboard Philae, sounded the near-surface of the small lobe in the 400–800 Hz range and determined a lower limit of ϵ′ equal to 2.45. We use a semi-empirical formula obtained from measurements of ϵ′ performed in the laboratory at 243 K on water ice and ice-basaltic dust mixtures, with a controlled porosity in the 31–91% range and a dust-to-ice volumetric ratio in the 0.1–2.8 range, to interpret the results of the two instruments, taking into account the temperature and frequency dependencies. A graphical method is proposed to derive ranges of porosity and dust-mass fraction from a value of ϵ′ derived from observations. The non-dispersive behaviour of ϵ′ below 175 K, allows us to compare the values of ϵ′ obtained by CONSERT and SESAME-PP. We show that the porosity of the small lobe of 67P increases with depth. Based on new measurements of analogues of complex extraterrestrial organic matter, the so-called tholins, we also suggest that, for the dust component in the cometary material, the presence of silicates has more effect on ϵ′ than organic materials.
Published: 2016
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16. Cosmochemical implications of CONSERT permittivity characterization of 67P/CG

Author: Jérémie Lasue, Anny Chantal Levasseur-Regourd, Sonia Zine, Pierre Beck, Wlodek Kofman, Alain Herique, Lydie Bonal, Ilaria Buttarazzi, Essam Heggy, Eric Quirico, Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), Ming Hsieh Department of Electrical Engineering [Los Angeles], USC Viterbi School of Engineering, University of Southern California (USC)-University of Southern California (USC), Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), PLANETO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), University of Southern California (USC), Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), Planeto, Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), IMPEC - LATMOS, Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), and Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)
Subjects: Permittivity, 67P/Churyumov-Gerasimenko, 010504 meteorology & atmospheric sciences, Comet, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Volatile, Mineralogy, Astrophysics, Dielectric, Radar astronomy, 01 natural sciences, Comet nucleus, 0103 physical sciences, Comets, Porosity, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, Refractory, [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], Astronomy and Astrophysics, [SDU.ASTR.IM]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Instrumentation and Methods for Astrophysic [astro-ph.IM], Depth sounding, 13. Climate action, Space and Planetary Science, Volume fraction, Radio wave
Abstract: International audience; Analysis of the propagation of the CONSERT signal throughout the small lobe of 67P/CG nucleus permitted to deduce the real part of the permittivity, at a value of 1.27± 0.05 [1]. The first interpretation of this value using the dielectric properties of mixtures of ices (H2O, CO2), dusts and porosity, led to the conclusion that the comet porosity ranges between 75 – 85%. In addition, the dust to ice ratio was found to range between 0.4-2.6 and the permittivity of dust (including 30% of porosity) was determined to be lower than 2.9. This last value corresponds to a permittivity lower than 4 for a material without any porosity.This paper is intended to refine the dust permittivity estimate by taking into account the updated values of nucleus densities and dust/ice ratio, and to provide further insights into the nature of the constituents of comet 67P/CG. We adopted a systematic approach: determination of the dust permittivity as a function of the Ice / Dust and Vacuum (i.e. porosity) volume fraction and comparison with the permittivity of meteoritic, mineral and organic material from literature and laboratory measurements. Then different composition models of the nuclei corresponding to cosmochemical endmembers of 67P/CG dust are tested. For each of these models the location in the I/D/V diagram is calculated based on available dielectric measurements, and confronted to the locus of 67P/CG. The number of compliant models is small and the cosmochemical implications of each are discussed to conclude on a preferred model [2]. An important fraction of carbonaceous material is required in the dust in order to match CONSERT permittivity observations, establishing that comets represent a massive carbon reservoir.[1] Kofman et al., Science, 349, 6247, aaa0639, 2015. [2] Herique et al., MNRAS, submitted, 2016.
Published: 2016
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17. A short review on the F1-region ion composition in the auroral and polar ionosphere

Author: C. Lathuillere, Wlodek Kofman, Laboratoire de Planétologie de Grenoble (LPG), and Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Atmospheric Science, 010504 meteorology & atmospheric sciences, Incoherent scatter, Aerospace Engineering, Incoherent scatter observations, Atmospheric sciences, 01 natural sciences, International Reference Ionosphere, 010305 fluids & plasmas, Ion, Electric field, 0103 physical sciences, Auroral ionosphere, Ionospheric heater, 0105 earth and related environmental sciences, Physics, Ion composition, Empirical modelling, Astronomy and Astrophysics, F1-region, Computational physics, Geophysics, Space and Planetary Science, Physics::Space Physics, General Earth and Planetary Sciences, Polar, Ionosphere
Abstract: International audience; Most F1 region ion composition measurements are obtained by the incoherent scatter technique. During magnetically quiet periods, we review all empirical models that have been obtained from EISCAT measurements. These models show comparable behaviour, which general trend is quite well described by the International Reference Ionosphere model. Specific attention is also given to the ion composition behaviour during magnetically active periods. The measurement problems are recalled. Measurements and simulations show that the molecular ions can dominate the F ionospheric layer when electric field are larger than 50 mV/m.
Published: 2006
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18. Permittivity measurements of porous matter in support of investigations of the surface and interior of 67P/Churyumov-Gerasimenko

Author: Nicolas Thomas, Essam Heggy, Pierre Encrenaz, Anny Chantal Levasseur-Regourd, Pierre Sabouroux, Wlodek Kofman, Yann Brouet, Physikalisches Institut [Bern], Universität Bern [Bern], IMPEC - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), HIPE (HIPE), Institut FRESNEL (FRESNEL), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique (LERMA), École normale supérieure - Paris (ENS Paris)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université de Cergy Pontoise (UCP), Université Paris-Seine-Université Paris-Seine-Centre National de la Recherche Scientifique (CNRS), USC Viterbi School of Engineering, University of Southern California (USC), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), PLANETO - LATMOS, Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université de Cergy Pontoise (UCP), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG ), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Universität Bern [Bern] (UNIBE), and École normale supérieure - Paris (ENS-PSL)
Subjects: Physics, Permittivity, 67P/Churyumov-Gerasimenko, comets: general, Comet, Attenuation length, Data analysis, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], comets: individual: 67P/Churyumov-Gerasimenko, Astronomy and Astrophysics, Astrophysics, techniques: radar astronomy, Radar astronomy, methods: data analysis, Mantle (geology), 13. Climate action, Space and Planetary Science, methods: laboratory: solid state, Comets, Millimeter, Coaxial, Porosity
Abstract: International audience; Permittivity measurements on porous samples of volcanic origin have been performed in the 0.05–190 GHz range under labo- ratory conditions in support of the Rosetta mission to comet 67P/Churyumov–Gerasimenko, specifically with the MIRO radiometric experiment and CONSERT radar experiment.Methods. The samples were split into several subsamples with different size ranges covering a few μm to 500 μm. Bulk densities of the subsamples were estimated to be in the 800 to 1500 kg/m3 range. The porosities were in the range of 48% to 65%. From 50 MHz to 6 GHz and at 190 GHz, permittivity has been determined with a coaxial cell and with a quasi-optical bench, respectively.Results. Without taking into account the volume-scattering effect at 190 GHz, the real part of the permittivity, normalized by the bulk density, is in the range of 2.1 to 2.6. The results suggest that the real part of the permittivity of an ice-free dust mantle covering the nucleus is in the 1.5−2.2 range at 190 GHz. From these values, a lower limit for the absorption length for the millimeter receiver of MIRO has been estimated to be between 0.6 and 2 cm, in agreement with results obtained from MIRO in September 2014. At frequencies of interest for CONSERT experiment, the real part of the permittivity of a suspected ice-free dust mantle should be below 2.2. It may be in the range of 1.2 to 1.7 for the nucleus, in agreement with first CONSERT results, taking into account a mean tem- perature of 110 K and different values for the dust-to-ice volumetric ratio. Estimations of contributions of the different parameters to the permittivity variation may indicate that the porosity is the main parameter.
Published: 2015
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19. CONSERT suggests a change in local properties of 67P/Churyumov-Gerasimenko's nucleus at depth

Author: Anny Chantal Levasseur-Regourd, Dirk Plettemeier, Yves Rogez, Christoph Statz, Wlodek Kofman, Jérémie Lasue, Alain Herique, Valérie Ciarletti, IMPEC - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut de recherche en astrophysique et planétologie (IRAP), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Technische Universität Dresden (TUD), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), PLANETO - LATMOS, Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Technische Universität Dresden = Dresden University of Technology (TU Dresden), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG ), Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Observatoire des Sciences de l'Univers de Grenoble (OSUG), and Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Permittivity, 67P/Churyumov-Gerasimenko, 010504 meteorology & atmospheric sciences, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Astrophysics, Dielectric, 01 natural sciences, Signal, law.invention, Optics, law, 0103 physical sciences, medicine, Comets, Radar, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, business.industry, Astronomy and Astrophysics, Space vehicles, Computational physics, medicine.anatomical_structure, Space and Planetary Science, Simulated data, Tomography, Numerical methods, business, Instruments, Nucleus
Abstract: International audience; After the successful landing of Philae on the nucleus of 67P/Churyumov-Gerasimenko, the Rosetta mission provided the first opportunity of performing measurements with the CONSERT tomographic radar in November 2014. CONSERT data were acquired during this first science sequence. They unambiguously showed that propagation through the smaller lobe of the nucleus was achieved. Aims. While the ultimate objective of the CONSERT radar is to perform the tomography of the nucleus, this paper focuses on the local characterization of the shallow subsurface in the area of Philae’s final landing site, specifically determining the possible presence of a permittivity gradient below the nucleus surface.Methods. A number of electromagnetic simulations were made with a ray-tracing code to parametrically study how the gradient of the dielectric constant in the near-subsurface affects the ability of CONSERT to receive signals.Results. At the 90 MHz frequency of CONSERT, the dielectric constant is a function of porosity, composition, and temperature. The dielectric constant values considered for the study are based on observations made by the other instruments of the Rosetta mission, which indicate a possible near-surface gradient in physical properties and on laboratory measurements made on analog samples. Conclusions. The obtained simulated data clearly show that if the dielectric constant were increasing with depth, it would have prevented the reception of signal at the CONSERT location during the first science sequence. We conclude from our simulations that the dielectric constant most probably decreases with depth.
Published: 2015
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20. Imaging of a scaled comet model from lab experiments

Author: Christelle Eyraud, Wlodek Kofman, J.-M. Geffrin, Alain Herique, HIPE (HIPE), Institut FRESNEL (FRESNEL), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG ), Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Observatoire des Sciences de l'Univers de Grenoble (OSUG), and Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Physics, [SPI.ELEC]Engineering Sciences [physics]/Electromagnetism, Microwave analogy, [SDU]Sciences of the Universe [physics], Comet, Reconstruction algorithm, Iterative reconstruction, Focus (optics), 3D Imaging, Remote sensing, Microwave tomography
Abstract: International audience; The main goal of CONSERT experiment is to reach information on the nucleus of the comet Churyumov-Gerasimenko/67P. In this contribution, we focus on microwave tomography and the study is conducted on an equivalent scaled model of the comet. A simple vectorial-induced current reconstruction algorithm is exploited to obtain qualitative maps of the scene. Imaging results of this test model have been performed from lab measurements.
Published: 2014
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21. Generation of atmospheric gravity waves associated with auroral activity in the polarFregion

Author: Mamoru Ishii, Ryoichi Fujii, Hiroyuki Shinagawa, Shin-ichiro Oyama, Yasuhiro Murayama, Stephan Buchert, and Wlodek Kofman
Subjects: Physics, Atmospheric Science, Ecology, Atmospheric wave, Incoherent scatter, Paleontology, Soil Science, Forestry, Geophysics, Aquatic Science, Oceanography, F region, Earth's magnetic field, Magnetogram, Space and Planetary Science, Geochemistry and Petrology, Dispersion relation, Physics::Space Physics, Earth and Planetary Sciences (miscellaneous), Polar, Gravity wave, Earth-Surface Processes, Water Science and Technology
Abstract: Relations between auroral activities and the generation of neutral-wind oscillations in the polar F region (150–300 km) were investigated using data from the European Incoherent Scatter (EISCAT) radar, the all-sky auroral camera, and the IMAGE (International Monitor for Auroral Geomagnetic Effects) magnetograms. We dealt with two cases: observations on March 1, 1995 (case 1), and on March 29, 1995 (case 2). For both cases the field-aligned component of the neutral-wind velocity estimated from EISCAT radar data had dominant oscillation periods of 20–30 min, which are longer than the typical Brunt-Vaisala period in the polar F region (≃13 min). The observed oscillations showed the downward propagation of the phase with time. These properties on the oscillation period and the phase are general ones of atmospheric gravity waves (AGWs). For case 1 the all-sky auroral images obtained at Kilpisjarvi showed the auroral arc extending in an almost zonal direction near a distance estimated using wave parameters derived from the equation of the dispersion relation for AGWs applicable to the observed oscillations. This suggested that the auroral arc appeared to be the effective generator of the observed oscillations. The comparison of observed phase lines with predicted ones using models by Francis [1974] and Kato et al. [1977] showed agreements between the two for both cases. The comparison suggests that effective parameters of the wave source in characterizing neutral-wind oscillations would be the horizontal distribution of the wave source and the distance between the observing point and the source region. It was concluded that geomagnetic activities on March 1 and 29, 1995, in northern Scandinavia significantly related to the generation of the observed oscillations. The conclusion implies that geomagnetic activities at high latitudes are an important source to generate AGWs, as indicated by previous theoretical studies.
Published: 2001
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22. Letter to the EditorEffects of hot oxygen in the ionosphere: TRANSCAR simulations

Author: A. Litvin, Wlodek Kofman, W. L. Oliver, Pierre-Louis Blelly, and D. Alcaydé
Subjects: Physics, Atmospheric Science, education.field_of_study, Computer simulation, Diurnal temperature variation, Population, Incoherent scatter, chemistry.chemical_element, Geology, Astronomy and Astrophysics, Noon, Atmospheric sciences, Oxygen, Physics::Geophysics, chemistry, Space and Planetary Science, Physics::Space Physics, Earth and Planetary Sciences (miscellaneous), Atomic oxygen, Astrophysics::Earth and Planetary Astrophysics, Ionosphere, education
Abstract: Recent studies of the ion energy balance in the mid-latitude ionosphere have led to the suggestion that hot neutral atomic oxygen may play a significant role; the presence of a population of hot O could explain some of the problems met in balancing the ion energy budget for Incoherent Scatter (IS) observations. The aim of the present study is to look at such effects by using numerical simulation. The TRANSCAR model is a time-dependent, 13-moment ionosphere model developed for high latitude studies. It was first adapted for mid-latitude conditions. In a first step the model was calibrated and cross-checked with St. Santin IS measurements for the winter case of 27 January 1972 around noon using, in particular, the MSIS neutral atmosphere model. This provides a reference diurnal variation of the ionosphere. The second step investigated the influence of a maxwellian population of hot neutral atomic oxygen introduced in addition to the standard neutral atmosphere. The paper describes the initial comparison between the model and St. Santin IS data, and then the effects induced by a hot atomic oxygen population.Key words. Ionosphere (ionosphere-atmosphere interactions; ion chemistry and composition; mid-latitude ionosphere)
Published: 2001
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23. Effects of auroral arcs on the generation of gravity waves in the auroral F-region

Author: Yasuhiro Murayama, Hiroyuki Shinagawa, Mamoru Ishii, Shin-ichiro Oyama, Stephan Buchert, Satonori Nozawa, Ryoichi Fujii, and Wlodek Kofman
Subjects: Physics, Atmospheric Science, Gravitational wave, Oscillation, Incoherent scatter, Phase (waves), Aerospace Engineering, Astronomy and Astrophysics, Astrophysics, Atmospheric sciences, F region, Electromagnetic radiation, Wavelength, Geophysics, Space and Planetary Science, Dispersion relation, General Earth and Planetary Sciences
Abstract: The relationship between auroral activity and the generation of gravity waves (GWs) in the auroral F -region (150–300 km) was investigated using data from the European Incoherent Scatter (EISCAT) radar and an all-sky camera at Kilpisjarvi (69.0° N, 20.8° E). The oscillations of neutrals observed with the EISCAT radar on 1 March 1995 had a dominant oscillation period of 24 min, which is longer than the typical Brunt-Vaisala period in the auroral F -region (≅ 13 min). According to the equation of the dispersion relation for GWs, the horizontal phase-velocity and the horizontal wavelength of the observed oscillations were about 110 m/s and about 160 km, respectively. The observed oscillations showed a downward propagation of the phase with time. Although we could not find conclusive evidence that the observed oscillations were GWs, the estimated characteristics of the observed oscillations were typical ones for the medium-scale GWs. The all-sky images showed that the auroral arc extended in an almost zonal direction near the source region estimated from the values of the observed wave-parameters. When the oscillations were compared with ones calculated using the Francis model, the phase lines of the modeled GWs showed agreement with those of the observed oscillations. Although we could not rule out the possibility of generating the observed oscillations by meteorological sources, enhancements of electromagnetic energy in association with the arc are considered to be strong candidate source to generate the observed oscillations.
Published: 2001
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24. Incoherent scatter technique applied to study the terrestrial ionosphere and thermosphere

Author: Wlodek Kofman
Subjects: Physics, law, Physics::Space Physics, Incoherent scatter, General Earth and Planetary Sciences, Ionospheric heater, Geophysics, Thermosphere, Radar, Ionosphere, Physics::Atmospheric and Oceanic Physics, Physics::Geophysics, law.invention
Abstract: In this review we describe the various methods to derive the ionospheric and atmospheric parameters from the incoherent scatter radar measurements. The measurement technique is shortly described, followed by a discussion on the ionospheric parameters analysis. From the ionospheric parameters and using the physical equations, the neutral atmospheric parameters, the density, temperatures and winds can be derived.
Published: 2000
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25. On the usefulness of E region electron temperatures and lower F region ion temperatures for the extraction of thermospheric parameters: a case study

Author: C. Cussenot, J.-P. St.-Maurice, and Wlodek Kofman
Subjects: Physics, Atmospheric Science, 010504 meteorology & atmospheric sciences, Geology, Astronomy and Astrophysics, Electron, Atmospheric sciences, 01 natural sciences, F region, Ion, Atmosphere, 13. Climate action, Space and Planetary Science, Electric field, Physics::Space Physics, 0103 physical sciences, Earth and Planetary Sciences (miscellaneous), Electron temperature, Atomic physics, Ionosphere, Thermosphere, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract: Using EISCAT data, we have studied the behavior of the E region electron temperature and of the lower F region ion temperature during a period that was particularly active geomagnetically. We have found that the E region electron temperatures responded quite predictably to the effective electric field. For this reason, the E region electron temperature correlated well with the lower F region ion temperature. However, there were several instances during the period under study when the magnitude of the E region electron temperature response was much larger than expected from the ion temperature observations at higher altitudes. We discovered that these instances were related to very strong neutral winds in the 110-175 km altitude region. In one instance that was scrutinized in detail using E region ion drift measurement in conjunction with the temperature observations, we uncovered that, as suspected, the wind was moving in a direction closely matching that of the ions, strongly suggesting that ion drag was at work. In this particular instance the wind reached a magnitude of the order of 350 m/s at 115 km and of at least 750 m/s at 160 km altitude. Curiously enough, there was no indication of strong upper F region neutral winds at the time; this might have been because the event was uncovered around noon, at a time when, in the F region, the E×B drift was strongly westward but the pressure gradients strongly northward in the F region. Our study indicates that both the lower F region ion temperatures and the E region electron temperatures can be used to extract useful geophysical parameters such as the neutral density (through a determination of ion-neutral collision frequencies) and Joule heating rates (through the direct connection that we have confirmed exists between temperatures and the effective electric field).Key words. Ionosphere (auroral ionosphere; ionosphere atmosphere interactions; plasma temperature and density)
Published: 1999
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26. A search for the location of the HF excitation of enhanced ion acoustic and langmuir waves with eiscat and the tromsø heater

Author: Michael T. Rietveld, Tor Hagfors, Thomas Leyser, C. LaHoz, Evgeny Mishin, Wlodek Kofman, and B. Isham
Subjects: Physics, Nuclear and High Energy Physics, Incoherent scatter, Astronomy and Astrophysics, Statistical and Nonlinear Physics, Plasma, Plasma oscillation, Electronic, Optical and Magnetic Materials, Ion, law.invention, Computational physics, Earth's magnetic field, Ultra high frequency, law, Physics::Space Physics, Electrical and Electronic Engineering, Radar, Excitation, Remote sensing
Abstract: In an effort to understand the mechanisms which give rise to the enhanced ion acoustic and Langmuir waves in HF modification experiments, we perform measurements with the EISCAT Tromso heater and the two incoherent scatter radars to locate the enhancement regions in space. Simultaneous measurements of the enhancements were made with both the VHF (224 MHz) and the UHF (933 MHz) radars, the latter being scanned in the magnetic meridian plane between vertical and field aligned through theSpitze angle. The results show that enhanced bottomside and topside ion acoustic and plasma waves at UHF and VHF are a common phenomena in these data. UHF topside enhanced plasma waves were not observed, possibly due to lack of radar sensitivity. At UHF the enhanced ion waves were strongest when the radar was pointed between theSpitze angle and geomagnetic field aligned direction. The topside features we believe give evidence for the production and propagation of Z-mode waves during this experiment. There is no evidence in these data for the decay of Z-mode waves into Bernstein and lower hybrid waves inside the overdense F layer as we believe to have observed previously.
Published: 1999
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27. A characterization of a comet nucleus interior

Author: G Caudal, Alain Herique, Wlodek Kofman, J.-P Ayanides, and Tor Hagfors
Subjects: Permittivity, Physics, business.industry, Astronomy and Astrophysics, Inversion (meteorology), WKB approximation, Computational physics, medicine.anatomical_structure, Optics, Space and Planetary Science, Comet nucleus, Permittivity distribution, Scale structure, medicine, Astrophysics::Earth and Planetary Astrophysics, Radio frequency, business, Nucleus
Abstract: Radio transmission through the nucleus of the comet Wirtanen, as developed in the CONSERT experiment on the ROSETTA mission, is designed to provide information on the electrical properties of the cometary interior. In order to determine what information can most readily be obtained, we first introduce an analytical model of the nucleus permittivity. We then use the WKB approximation to describe the propagation of waves through the nucleus model assuming a radio frequency of 90 MHz, the frequency chosen for the experiment. With one end of the propagation path on the surface of the comet, and the other in a vehicle orbiting the nucleus, it is shown that the signal at the orbiting end of the path must be back-propagated to the surface of the nucleus of the comet in order to obtain a correct interpretation of the data. We show how the mean permittivity along each propagation path can be obtained and how this can be used to obtain information about the large scale structure of the nucleus. Finally we discuss how the permittivity distribution found can be used to constrain the nature of the material in the interior of the nucleus. © 1999 Elsevier Science Ltd. All rights reserved.
Published: 1999
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28. Aspect angle dependence of HF enhanced incoherent backscatter

Author: Thomas Leyser, Michael T. Rietveld, Wlodek Kofman, Evgeny Mishin, Tor Hagfors, A. P. van Eyken, B. Isham, and C. La Hoz
Subjects: Physics, Atmospheric Science, Backscatter, Langmuir Turbulence, Transmitter, Incoherent scatter, Aerospace Engineering, Astronomy and Astrophysics, Geophysics, Space and Planetary Science, Aspect angle, Physics::Space Physics, General Earth and Planetary Sciences, Uhf radar, Ionosphere, Physics::Atmospheric and Oceanic Physics, Remote sensing
Abstract: An HF ionospheric interaction experiment was performed in November and December of 1997 using the EISCAT HF transmitter and 931 and 224 MHz incoherent scatter radars, all co-located near Tromso, Norway. During this experiment the pointing of the UHF radar
Published: 1999
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29. A two dimensional simulation of the CONSERT experiment (radio tomography of comet Wirtanen)

Author: Wlodek Kofman, Alain Herique, S. Leblanc, A. Portal, and Jean-Pierre Barriot
Subjects: Physics, Permittivity, Atmospheric Science, business.industry, Comet, Phase (waves), Aerospace Engineering, Astronomy and Astrophysics, Covariance, Computational physics, Tikhonov regularization, Depth sounding, Geophysics, Optics, Space and Planetary Science, Comet nucleus, General Earth and Planetary Sciences, Astrophysics::Earth and Planetary Astrophysics, business, Radio wave
Abstract: We simulate two-dimensional (2-D) maps of the internal permittivity of comet Wirtanen from CONSERT (Comet Nucleus Sounding Experiment by Radiowave Transmission) phase measurements. We study the influence of a priori covariance matrices on the mapping process through Tikhonov or linear regression inverse formulas. We show that this a priori information permits a smooth imaging of the internal permittivity, sometimes affected by ghosts (false anomalies). Accounting for indirect propagation paths through the comet material (rays totally reflected by the comet surface) can alleviate this problem.
Published: 1999
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30. Comet nucleus sounding experiment by radiowave transmission

Author: Peter Edenhofer, Erling Nielsen, J. Veverka, H. Kochan, Roberto Seu, Tor Hagfors, J. Klinger, Paul R. Weissman, C. Elachi, Anny Chantal Levasseur-Regourd, Alain Herique, J.J. van Zyl, Iwan P. Williams, J. Melosh, Yves Barbin, Eberhard Grün, Svein-Erik Hamran, L. H. Svedhem, Wlodek Kofman, Giovanni Picardi, Jean-Pierre Barriot, Centre d'Études des Phénomènes Aléatoires et Géophysiques (CEPHAG), École Nationale Supérieure d'Ingénieurs Électriciens de Grenoble (ENSIEG)-Centre National de la Recherche Scientifique (CNRS), Service d'aéronomie (SA), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Laboratoire de glaciologie et géophysique de l'environnement (LGGE), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS), Groupement de Recherche en Géodésie Spatiale (GRGS), Centre National d'Études Spatiales [Toulouse] (CNES), Max-Planck-Institut für Aeronomie (MPI Aeronomie), Max-Planck-Gesellschaft, Max-Planck-Institut für Kernphysik (MPIK), Institute for High-Frequency Technique [Bochum], Ruhr-Universität Bochum [Bochum], DLR Institut für Raumsimulation, Deutsches Zentrum für Luft- und Raumfahrt [Köln] (DLR), Dipartimento INFOCOM [Roma], Università degli Studi di Roma 'La Sapienza' [Rome], Jet Propulsion Laboratory (JPL), California Institute of Technology (CALTECH)-NASA, Cornell University, European Space Research and Technology Centre (ESTEC), European Space Agency (ESA), Queen Mary's College [Chennai], Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Università degli Studi di Roma 'La Sapienza' = Sapienza University [Rome] (UNIROMA), NASA-California Institute of Technology (CALTECH), Cornell University [New York], Agence Spatiale Européenne = European Space Agency (ESA), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), and Università degli Studi di Roma 'La Sapienza' = Sapienza University [Rome]
Subjects: Atmospheric Science, 010504 meteorology & atmospheric sciences, Comet, Aerospace Engineering, 01 natural sciences, Electromagnetic radiation, law.invention, Orbiter, law, Comet nucleus, 0103 physical sciences, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Radio Science, Remote sensing, Physics, Astronomy and Astrophysics, Depth sounding, Radio propagation, Geophysics, [SDU]Sciences of the Universe [physics], Space and Planetary Science, Physics::Space Physics, General Earth and Planetary Sciences, Astrophysics::Earth and Planetary Astrophysics, Radio wave
Abstract: International audience; We describe the radio science experiment proposed for the Rosetta cometary mission. The experiment consists in the transmission of electromagnetic waves between the landers and the orbiter through the comet to study its internal structure. In the paper, the electromagnetic model of the comet is presented and used to evaluate the potentiality of the experiment. Various modellings of the radio wave propagation are discussed. Finally, a description of the experiment and the instrument is made.
Published: 1998
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31. On origin of outshifted plasma lines during HF modification experiments

Author: Tor Hagfors, Wlodek Kofman, and Evgeny Mishin
Subjects: Physics, Atmospheric Science, Ecology, Scattering, Incoherent scatter, Paleontology, Soil Science, Forestry, Electron, Aquatic Science, Ponderomotive force, Oceanography, Geophysics, Space and Planetary Science, Geochemistry and Petrology, Spectral width, Earth and Planetary Sciences (miscellaneous), Reflection (physics), Ionosphere, Atomic physics, Earth-Surface Processes, Water Science and Technology, Radio wave
Abstract: Outshifted I)lasma lines, observed during injections of intense HF ra(tiowaves into the ioosphere, are due to scattering on Langlnuir waves with an unusually large spectral widi, h shifted above the injected frequency. Incoherent scatter radar observations reveal that these waves sometimes are located at altitudes exceeding by several kilolneters the altitude of the reflection layer of the ordinary HF wave, titus making an explanation in terlns of the so-called "free mode" problematic. We show that these olservations may be consistently described by the creation, (lue to the ponderomotive force, of density depletions in the Airy pattern of the Z ito(le. Tlte geileration of Langmuir plasmons by accelerated suprathermal electrons itside the depletions causes the wide spectral width of these plasma line features and their Inean frequency shift.
Published: 1997
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32. Proton transport model in the ionosphere: 1. Multistream approach of the transport equations

Author: Marina Galand, Jean Lilensten, Roger B. Sidje, and Wlodek Kofman
Subjects: Physics, Atmospheric Science, Ecology, Proton, Paleontology, Soil Science, Forestry, Electron, Aquatic Science, Oceanography, Kinetic energy, Boltzmann equation, Computational physics, Elastic collision, Geophysics, Space and Planetary Science, Geochemistry and Petrology, Proton transport, Earth and Planetary Sciences (miscellaneous), Atomic physics, Energy source, Convection–diffusion equation, Earth-Surface Processes, Water Science and Technology
Abstract: The suprathermal particles, electrons and protons, coming from the magnetosphere and precipitating into the high-latitude atmosphere are an energy source of the Earth's ionosphere. They interact with ambient thermal gas through inelastic and elastic collisions. The physical quantities perturbed by these precipitations, such as the heating rate, the electron production rate, or the emission intensities, can be provided in solving the kinetic stationary Boltzmann equation. This equation yields particle fluxes as a function of altitude, energy, and pitch angle. While this equation has been solved through different ways for the electron transport and fully tested, the proton transport is more complicated. Because of charge-changing reactions, the latter is a set of two-coupled transport equations that must be solved: one for protons and the other for H atoms. We present here a new approach that solves the multistream proton/hydrogen transport equations encompassing the collision angular redistributions and the magnetic mirroring effect. In order to validate our model we discuss the energy conservation and we compare with another model under the same inputs and with rocket observations. The influence of the angular redistributions is discussed in a forthcoming paper.
Published: 1997
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33. [Untitled]

Author: P. Louarn, J. M. Nappa, L. Friel, Wlodek Kofman, N. Cornilleau-Wehrlin, R. Manning, S. Perraut, P. Robert, C. de Villedary, D. Hubert, F. Wouters, Laurence Rezeau, Jean-Louis Pinçon, Y. de Conchy, C. Lacombe, A. Meyer, François Lefeuvre, S. Louis, Michel Parrot, A. Roux, B. Poirier, C. C. Harvey, and P. Chauveau
Subjects: Electromagnetic field, Physics, Spectrum analyzer, 010504 meteorology & atmospheric sciences, Field (physics), Dynamic range, Magnetometer, Acoustics, Astronomy and Astrophysics, 01 natural sciences, law.invention, Search coil, Solar wind, Nuclear magnetic resonance, Space and Planetary Science, law, 0103 physical sciences, Waveform, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract: The Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment is one of five experiments which together comprise the Wave Experiment Consortium (WEC). STAFF consists of a three-axis search coil magnetometer to measure magnetic fluctuations at frequencies up to 4 kHz, and a spectrum analyser to calculate in near-real time aboard the spacecraft, the complete auto- and cross-spectral matrices using the three magnetic and two electric components of the electromagnetic field. The magnetic waveform at frequencies below either 10 Hz or 180 Hz is also transmitted. The sensitivity of the search coil is adapted to the phenomena theo be studied: the values 3 × 10-3 nT Hz-1/2 and 3 × 10-5 nT Hz-1/2 are achieved respectively at 1 Hz and 100 Hz. The dynamic range of the STAFF instruments is about 96 dB in both waveform and spectral power, so as to allow the study of waves near plasma boundaries. Scientific objectives of the STAFF investigations, particularly those requiring four point measurements, are discussed. Methods by which the wave data will be characterised are described with emphasis on those specific to four-point measurements, including the use of the Field Energy Distribution function.
Published: 1997
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34. Auroral ionospheric conductivities: a comparison between experiment and modeling, and theoretical f10.7-dependent model for EISCAT and ESR

Author: Wlodek Kofman, D. Alcaydé, J. Lilensten, and Pierre-Louis Blelly
Subjects: Physics, Atmospheric Science, 010504 meteorology & atmospheric sciences, Solar zenith angle, Geology, Astronomy and Astrophysics, Statistical model, Geophysics, 01 natural sciences, law.invention, Hall conductivity, Computational physics, Space and Planetary Science, law, Dependent model, 0103 physical sciences, Earth and Planetary Sciences (miscellaneous), Range (statistics), Ionosphere, Radar, 010303 astronomy & astrophysics, Zenith, 0105 earth and related environmental sciences
Abstract: Several authors have published models of auroral conductances in the past. Some of them are based on theoretical approaches; others are the result of observations. The data bases for the latter models range from 8 h to 3 years of experiments. In this paper, we show the results of our own modeling, based on a coupled ki- netic/fluid approach. We compare these results to the sta- tistical model based on 3 years of experiment. We then model the auroral ionospheric conductances above EISCAT and the EISCAT-Svalbard Radar for different solar-activity indices. These modeled conductances are fitted with a simple law depending on the f10.7 index and on the solar zenith angle.
Published: 1996
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35. Non-thermal ionospheric plasma studies using the incoherent scatter technique

Author: J.-P. St-Maurice and Wlodek Kofman
Subjects: Physics, Thermal equilibrium, Atmospheric Science, General Engineering, Incoherent scatter, Geophysics, Plasma, F region, Computational physics, Electric field, Thermal, General Earth and Planetary Sciences, Electron temperature, Ionosphere, General Environmental Science
Abstract: Non-thermal phenomena are a common occurrence in the aurora] ionosphere. The incoherent scatter technique is now frequently used to study several of the features associated with the departure of the plasma from a thermal equilibrium configuration. In this review we limit our discussion to E and F region phenomena. The first observation that we discuss is that of a large increase in the auroral E region electron temperature during periods of strong convection electric fields. We illustrate these observations with a few examples and summarize the current state of the theoretical debate on electron heating by turbulent ion-acoustic waves. Strongly asymmetric incoherent scatter spectra offer a second example of the effect of ion-acoustic turbulence on the wave spectra. We describe the observations and review three different possible physical mechanisms which have been proposed in the literature. The final part of this review deals with the signature of non-Maxwellian ion velocity distributions on incoherent scatter spectra. These non-Maxwellian distributions appear in the presence of a strong electric field. The first theories dealing with the creation of these distributions and with its effect on the incoherent scatter spectrum were developed in the mid-1970s and evolved in the 1980s. The most important problem, currently, is with the interpretation in terms of ionospheric parameters of the incoherent scatter spectra during the disturbed periods that lead to the non-Maxwellian signatures. We emphasize recent advances in the data analysis and discuss the remaining limitations while evaluating the direction of future work on this subject.
Published: 1996
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36. Comparison between EISCAT UHF and VHF backscattering cross section

Author: Wlodek Kofman, Hermann Opgenoorth, and B. Cabrit
Subjects: Physics, Atmospheric Science, Ecology, Scattering, Anomaly (natural sciences), Incoherent scatter, Paleontology, Soil Science, Forestry, Geophysics, Aquatic Science, Oceanography, Computational physics, Cross section (physics), Orders of magnitude (time), Ultra high frequency, Space and Planetary Science, Geochemistry and Petrology, Thermal, Earth and Planetary Sciences (miscellaneous), Ionosphere, Earth-Surface Processes, Water Science and Technology
Abstract: We present a comparison between the backscattering cross sections at 224 and 933 MHz measured with European Incoherent Scatter (EISCAT) radars during the passage of a discrete arc. It shows a difference of 2 orders of magnitude which cannot simply be explained by normal thermal ionospheric density fluctuations. We claim that the observed difference in the scattering cross sections is due to so-called anomalous echoes which typically occur in the vicinity of high-altitude ionospheric perturbations, caused by low-energy particle precipitation. Two possible explanations for the observed differences are discussed: spatial localization and k dependence. Using UHF tristatic observations, we show that there, indeed, is a possibility that the observed echoes are very localized in space. Analyzing the possible k dependence, we show that the experimental geometry used at least in principle will allow us to rule out one of the earlier proposed production mechanisms.
Published: 1996
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37. In situ generation of intense parallel electric fields in the lower ionosphere

Author: Wlodek Kofman, J.-P. St.-Maurice, and D. James
Subjects: Physics, Atmospheric Science, Ecology, Field (physics), Field line, Paleontology, Soil Science, Electron precipitation, Forestry, Plasma, Geophysics, Aquatic Science, Oceanography, Ion acoustic wave, Computational physics, Space and Planetary Science, Geochemistry and Petrology, Electric field, Earth and Planetary Sciences (miscellaneous), Ionosphere, Current density, Earth-Surface Processes, Water Science and Technology
Abstract: The authors look at simple models which could generate intense electric fields, on the order of millivolts per meter in the ionosphere. Such field strenths are implied by a number of different ionospheric observations of electric fields, currents, and plasma waves. They concentrate on the possible existence of quasistatic fields on timescales of electron collision times or the Alfven transit time. They draw conclusions with regard to horizontal gradient scale lengths, namely that 100 m horizontal gradient scales are required, or for longer gradient scales, then return currents are shown to flow along the same paths as precipitating electrons, and hence current densities parallel to field lines are substantially decreased.
Published: 1996
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38. Natural radio emission of Jupiter as interferences for radar investigations of the icy satellites of Jupiter

Author: Baptiste Cecconi, Donald D. Blankenship, Lorenzo Bruzzone, Alain Herique, Daniel Santos-Costa, Wlodek Kofman, Jean-Louis Bougeret, Giovanni Alberti, Sebastien Hess, M. R. Santovito, Ph. Zarka, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Helmholtz zentrum für Schwerionenforschung GmbH (GSI), UJF-Grenoble I/CNRS, Université Joseph Fourier - Grenoble 1 (UJF), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG ), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Faculty of Environment and Natural Resources, University of Freiburg [Freiburg], University of Trento [Trento], Ingénieurs, Techniciens et Administratifs, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and Physique des plasmas
Subjects: 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Cosmology and Extragalactic Astrophysics, 7. Clean energy, 01 natural sciences, Radio spectrum, Jovian, law.invention, Radio telescope, Jupiter, symbols.namesake, Exploration of Jupiter, law, 0103 physical sciences, Radar, 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Remote sensing, Physics, [PHYS]Physics [physics], Europa Orbiter, Astronomy, Astronomy and Astrophysics, Galilean moons, 13. Climate action, Space and Planetary Science, Physics::Space Physics, symbols, Astrophysics::Earth and Planetary Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract: Radar instruments are part of the core payload of the two Europa Jupiter System Mission (EJSM) spacecraft: NASA-led Jupiter Europa Orbiter (JEO) and ESA-led Jupiter Ganymede Orbiter (JGO). At this point of the project, several frequency bands are under study for radar, which ranges between 5 and 50 MHz. Part of this frequency range overlaps with that of the natural jovian radio emissions, which are very intense in the decametric range, below 40 MHz. Radio observations above 40 MHz are free of interferences, whereas below this threshold, careful observation strategies have to be investigated. We present a review of spectral intensity, variability and sources of these radio emissions. As the radio emissions are strongly beamed, it is possible to model the visibility of the radio emissions, as seen from the vicinity of Europa or Ganymede. We have investigated Io-related radio emissions as well as radio emissions related to the auroral oval. We also review the radiation belts synchrotron emission characteristics. We present radio sources visibility products (dynamic spectra and radio source location maps, on still frames or movies), which can be used for operation planning. This study clearly shows that a deep understanding of the natural radio emissions at Jupiter is necessary to prepare the future EJSM radar instrumentation. We show that this radio noise has to be taken into account very early in the observation planning and strategies for both JGO and JEO. We also point out possible synergies with RPW (Radio and Plasma Waves) instrumentations.
Published: 2012
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39. PSTD-based approach to a large-scale inverse scattering problem

Author: Sebastian Hegler, Christoph Statz, Alain Herique, Dirk Plettemeier, Wlodek Kofman, and Gabriel Arnold
Subjects: Physics, Wavelength, Scale (ratio), Wave propagation, Permittivity distribution, Inverse scattering problem, Mathematical analysis, Finite-difference time-domain method, Electromagnetic wave scattering, Inverse problem, Algorithm
Abstract: The three-dimensional finite-difference time-domain method (FDTD) simulation of electromagnetic wave propagation in large structures, like the cometary nucleus of 67P/Churyumov-Gerasimenko, as well as the inverse problem of reconstructing the permittivity distribution inside the comet nucleus is computationally expensive. With approximative methods not all propagation phenomena can be sufficiently modeled. For the efficient solution of this kind of inverse problem we propose the use of pseudo-spectral time-domain method (PSTD). This method overcomes the computational burdens and memory demands of the FDTD and allows accurate modeling of wave propagation for the CoNSERT case. In combination with optimal checkpointing and a state-of-the-art optimization tool, we demonstrate the solution of inverse problems at a scale of 50 wavelengths.
Published: 2011
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40. Appearance of layered structures in numerical simulations of polydisperse bodies accretion: Application to cometary nuclei

Author: Jérémie Lasue, Wlodek Kofman, Anny Chantal Levasseur-Regourd, Edith Hadamcik, Robert Botet, Los Alamos National Laboratory (LANL), Lunar and Planetary Institute [Houston] (LPI), Laboratoire de Physique des Solides (LPS), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), IMPEC - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Université Paris-Sud - Paris 11 (UP11), PLANETO - LATMOS, Institut de Planétologie et d'Astrophysique de Grenoble (IPAG ), Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Observatoire des Sciences de l'Univers de Grenoble (OSUG), and Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Solar System, Accretion, 010504 meteorology & atmospheric sciences, [PHYS.ASTR.EP]Physics [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Gaussian, Collisional physics, Comet, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], 01 natural sciences, Power law, Molecular physics, symbols.namesake, Fractal, 0103 physical sciences, Homogeneity (physics), medicine, Comets, origin, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, nucleus, Interiors, Astronomy and Astrophysics, Classical mechanics, medicine.anatomical_structure, 13. Climate action, Space and Planetary Science, symbols, Exponent, Astrophysics::Earth and Planetary Astrophysics, Nucleus
Abstract: International audience; A model for the aggregation of size distribution of cometesimals (Gaussian or power law) into cometary nuclei is developed. Upon disruption induced by collisions, sticking and evolution of the tensile strength and density of the cometesimals by sintering processes are taken into account. The resulting cometary nuclei present specific internal structures that have been quantified to allow the comparison with observational constraints and future in situ observations and cometary nucleus sounding with the CONSERT radar on-board the Rosetta mission. A parameter called the homogeneity exponent, μ, determines different aggregation regimes. Fractal aggregates are formed for μ
Published: 2011
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41. A new scenario for the measurement of the auroral plasma parameters in the non-Maxwellian state

Author: N. Bonnard, Wlodek Kofman, C. Lathuillere, and D. Hubert
Subjects: Physics, Electron density, Geophysics, Distribution function, Physics::Plasma Physics, Plasma parameters, General Earth and Planetary Sciences, Electron temperature, Plasma, Atomic physics, Temperature measurement, Charged particle, Ion
Abstract: The O+ and NO+ ion velocity distributions in the presence of a large electric field are analytically calculated for the auroral F region, taking into account the collisions with atomic and molecular neutral constituents. We have found an angle of 21°± 1° with respect to the magnetic field direction where the O+ one-dimensional line-of-sight velocity distributions display a Maxwellian shape while the NO+ distribution function is nearly a Maxwellian. A scenario for the measurement of the auroral plasma parameters is discussed. The radar spectrum obtained for the specific angle of 21° depends on five parameters : electron density, electron temperature, ion composition, and two ion line-of-sight temperatures. With this reduced number of plasma parameters the fit from radar spectra is nevertheless ambiguous. To resolve this dilemma it is necessary to get an independent measurement of one of these five parameters. The plasma line observation is shown to provide a simultaneous measurement of the electron temperature. From simultaneous measurements of the ion line-of-sight temperatures, made at an angle away from 21° the termodynamical temperature, as well as the ion temperature anisotropies, would be determined.
Published: 1993
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42. Heat flow effect on the plasma line frequency

Author: A. P. van Eyken, J.-P. St-Maurice, and Wlodek Kofman
Subjects: Atmospheric Science, Incoherent scatter, Soil Science, Electron, Aquatic Science, Oceanography, Plasma oscillation, Optics, Physics::Plasma Physics, Geochemistry and Petrology, Dispersion relation, Earth and Planetary Sciences (miscellaneous), Center frequency, Earth-Surface Processes, Water Science and Technology, Physics, Ecology, business.industry, Paleontology, Forestry, Plasma, Geophysics, Heat flux, Space and Planetary Science, Physics::Space Physics, Electron temperature, Atomic physics, business
Abstract: Recent high-resolution studies of the electron plasma line show that the difference between the upshifted and the downshifted frequency does not depend only on the electron drift in the plasma and on the electron temperature through the classical dispersion relation using the Maxwellian electron distribution. The difference contains an additional strong nonlinear dependence on the electron temperature. We show here that the origin of this shift in the center frequency between the upshifted and downshifted lines can easily be due to heat flows {n the electron gas. We present a new expression for the dispersion relation that includes the heat flow contribution, and we use a recently acquired data set to demonstrate that the heat flow correction produces the right kind of results. For radar frequencies around 1000 MHz and plasma frequencies of the order of 7 MHz, this means that an electron temperature gradient of the order of 1 K/km can produce a difference approaching 500 Hz between the upshifted and downshifted frequencies. This shift in frequency is important, as it is comparable to the shift caused by parallel currents of a few microamperes per square meter.
Published: 1993
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43. Auroral ionospheric and thermospheric measurements using the incoherent scatter technique

Author: Wlodek Kofman
Subjects: Physics, Electron density, Incoherent scatter, Geophysics, Electron, Computational physics, Ion, Collision frequency, Geochemistry and Petrology, Physics::Space Physics, Ionospheric heater, Thermosphere, Ionosphere
Abstract: The incoherent scatter technique has been applied since 1965 to study the ionosphere and thermosphere in different regions of the Earth. The analysis of the received signal gives access to several ionospheric parameters as a function of height: electron density, electron and ion temperatures and ion velocity. The derivation of these parameters is usually a complicated mathematical procedure that requires a non-linear regression program. A lot of research has been done in the ionospheric and atmospheric science using this technique. In this paper we describe how one derives the ion-neutral collision frequency and the ion composition parameters. It is usually difficult to retrieve these parameters with the incoherent scatter technique; as a result, in the standard data analysis procedure, an ionospheric model is used instead. However the numerical values chosen in the model have an influence on the other derived parameters. For instance the choice of a wrong ion composition leads to erroneous plasma temperatures. It is therefore important to assess by how much the standard procedure deviates from reality. For this reason we compare the ion composition and collision frequency retrieved from a sophisticated analysis scheme with the values that are derived from models under similar geophysical conditions. It also possible to derive from the observed ionospheric parameters the neutral concentrations, temperatures and winds, by using the energy and momentum equations for the ions and the neutrals. In this paper the different methods and the corresponding assumptions involved in the data analysis are discussed. We describe the influence of the frictional heating, of the vertical neutral wind and of the ionospheric perturbations on the derivation of the neutral atmospheric parameters. Our discussion of the processes involved are drawn from results obtained by Chatanika, Sondrestrom and EISCAT radars.
Published: 1992
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44. Energy deposition in the E and F regions of the high-latitude ionosphere

Author: Wlodek Kofman and Jean Lilensten
Subjects: Physics, Atmospheric Science, Incoherent scatter, Aerospace Engineering, Astronomy and Astrophysics, Atmospheric sciences, F region, Physics::Geophysics, Geophysics, Space and Planetary Science, High latitude, Physics::Space Physics, General Earth and Planetary Sciences, Ionospheric heater, Ionosphere, Thermosphere, Deposition (chemistry), Energy (signal processing)
Abstract: A review of the different phenomena that contribute to heating the high-latitude ionosphere is given, along with an examination of their relative importances. Results of different experiments are shown as well as comparisons with the predictions of first-principles computer models.
Published: 1992
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45. Mapping of overspread targets in radar astronomy

Author: Tor Hagfors and Wlodek Kofman
Subjects: Physics, business.industry, Transmitter, Modulated continuous wave, Condensed Matter Physics, Noise (electronics), law.invention, symbols.namesake, Signal-to-noise ratio, Optics, Modulation, Gaussian noise, law, symbols, General Earth and Planetary Sciences, Waveform, Electrical and Electronic Engineering, Radar, business, Algorithm
Abstract: The problem of delay-Doppler mapping of overspread targets, i.e., targets where the product of delay-extent theta(t) and Doppler width B(t) is greater than unity, is discussed. For a transmitter modulation waveform which is believed to be representative of continuous wave modulation, namely, a random Gaussian noise modulation, the effect of the 'self-noise' and the additive noise on the output signal-to-noise ratio is evaluated, and expressions are derived which allow the signal-to-noise ratio to be predicted an the quality of the mapping assessed for various types of targets and modulation waveform properties. The problem of the self-noise is shown to be a serious problem, particularly for targets where the power returned varies greatly with range. A scheme involving a combination of random noise modulation and polarization modulation is developed which will greatly improve the capability to map this type of overspread targets. The particular case of the mapping of Mars with an existing facility is dealt with in detail, and it is shown that a limited amount of mapping with a resolution corresponding to 100 by 100 points on the planet is possible in certain regions. 19 refs.
Published: 1991
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46. Evidence of anisotropic temperatures of molecular ions in the auroral ionsphere

Author: C. La Hoz, D. Hubert, C. Lathuillere, and Wlodek Kofman
Subjects: Physics, business.industry, Incoherent scatter, F region, Charged particle, Spectral line, Computational physics, Geophysics, Optics, Electric field, General Earth and Planetary Sciences, Electron temperature, Ionosphere, Anisotropy, business
Abstract: Using incoherent scatter measurements obtained from Kiruna and Sodankyla EISCAT remote stations, and corresponding to different aspect angles, the authors show, for the first time, anisotropic temperatures of molecular ions. The electric field obtained for the 5 hours period of the 2nd February 1990 experiment presented here range from 20 to 50 mV/m. They show that the line of sight ion temperature deduced from Kiruna incoherent scatter spectra is larger than the one deduced from Sodankyla spectra which correspond to a smaller aspect angle. A statistical approach has been chosen to evaluate a {beta} parameter for Sodankyla measurements which describes the anisotropy. They found a value of 0.60 {plus minus} 0.02 which compares very well with values inferred from theoretical studies.
Published: 1991
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47. Observations of aurorae by SPICAM ultraviolet spectrograph on board Mars Express: Simultaneous ASPERA-3 and MARSIS measurements

Author: F. Leblanc, Ali Safaenili, Jasper Halekas, Hans Nilsson, Yoshifumi Futaana, J. D. Winningham, Wlodek Kofman, David Brain, Jeremie Mouginot, Olivier Witasse, Jean Lilensten, R. A. Frahm, J. L. Bertaux, Mats Holmström, and Rickard Lundin
Subjects: Atmospheric Science, Electron spectrometer, 010504 meteorology & atmospheric sciences, Soil Science, MARSIS, Astrophysics, Aquatic Science, Oceanography, 01 natural sciences, Atmosphere, Geochemistry and Petrology, 0103 physical sciences, Earth and Planetary Sciences (miscellaneous), 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Earth-Surface Processes, Water Science and Technology, Martian, Physics, Ecology, Total electron content, Paleontology, Forestry, Geophysics, Mars Exploration Program, Atmosphere of Mars, 13. Climate action, Space and Planetary Science, Ionosphere
Abstract: We present a new set of observations of Martian aurorae obtained by Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) on board Mars Express (MEX). Using nadir viewing, several auroral events have been identified on the Martian nightside, all near regions of crustal magnetic fields. For most of these events, two to three consecutive events with variable intensities and separated by a few seconds to several tens of seconds have been observed, whereas simultaneous observations with Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) and Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) have been possible. In this paper, we present the data set for these events and discuss the possible correlation between the measured UV emission by SPICAM, the measured downward and/or upward flux of electrons by ASPERA-3 and the total electron content recorded by MARSIS. Despite the limited coverage of SPICAM ultraviolet spectrograph (UVS) on the Martian nightside (essentially in regions of high crustal magnetic fields), there is however a very good correlation between the regions with the locally smallest probability to be on closed crustal magnetic field lines, as derived from Mars Global Surveyor/Electron Reflectometer (MGS/MAG-ER), and the position of an aurora event. This suggests that the crustal magnetic fields, when organized into cusp-like structure, can trigger the few aurorae identified by SPICAM UVS. It confirms also the good probability, in the cases where SPICAM UVS measured UV emissions, that the increase in the measured total electron content by MARSIS and the simultaneous measured precipitating electron flux by the ASPERA-3/Electron Spectrometer may be related to each other.
Published: 2008
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48. Correction of the ionospheric distortion on the MARSIS surface sounding echoes

Author: Ali Safaeinili, Wlodek Kofman, Alain Herique, Jeremie Mouginot, Laboratoire de Planétologie de Grenoble (LPG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Jet Propulsion Laboratory (JPL), and NASA-California Institute of Technology (CALTECH)
Subjects: Physics, 010504 meteorology & atmospheric sciences, Total electron content, Solar zenith angle, Mars, Astronomy and Astrophysics, MARSIS, Mars Exploration Program, Geophysics, Ionospheric dispersion compensation, 01 natural sciences, Ionospheric sounding, Physics::Geophysics, Space and Planetary Science, Martian surface, 0103 physical sciences, Physics::Space Physics, Radio occultation, Astrophysics::Earth and Planetary Astrophysics, Ionosphere, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract: International audience; Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on the Mars Express (MEX) spacecraft has made numerous measurements of the Martian surface and subsurface. However, all of these measurements are distorted by the ionosphere and must be compensated before any analysis. We have developed a technique to compensate for the ionospheric distortions. This technique provides a powerful tool to derive the total electron content (TEC) and other higher-order terms of the limited expansion of the plasma dispersion function that are related to overall shape of the electron column profile. The derived parameters are fitted by using a Chapman model to derive ionospheric parameters like n0, electron density primary peak (maximum for solar zenith angle (SZA) equal 0), and the neutral height scale H. Our estimated ionospheric parameters are in good agreement with Mars Global Surveyor (MGS) radio-occultation data. However, since MARSIS does not have the observation geometry limitations of the radio occultation measurements, our derived parameters extend over a large range of SZA for each MEX orbit. The first results from our technique have been discussed by Safaeinili et al. [2007, Estimation of the total electron content of the Martian ionosphere using radar sounder surface echoes. Geophys. Res. Lett. 34, L23204, doi:10.1029/2007GL032154].
Published: 2008
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49. Co-ordinated EISCAT-MICADO interferometer measurements of neutral winds and temperatures in E- and F-regions

Author: C. Senior, F Barlier, Wlodek Kofman, Gérard Thuillier, M. Hersé, D Alcayde, J. Fontanari, C. Lathuillere, and M. L. Duboin
Subjects: Physics, Atmospheric Science, General Engineering, Measure (physics), Michelson interferometer, F region, Wind speed, law.invention, Interferometry, Geophysics, law, General Earth and Planetary Sciences, Radar, Thermosphere, General Environmental Science, Remote sensing
Abstract: The MICADO instrument has been built to measure temperature and wind in the E - and F -regions. It employs a thermally stable field-compensated Michelson interferometer to allow wind measurements. During the winter of 1988–1989, the MICADO instrument was operated at Sodankyla (67°22′N, Finland). Measurements were made by observing the O 1 S (low thermosphere) and the O 1 D lines (high thermosphere) emission. Two co-ordinated campaigns were organized with the EISCAT radar, which operated in special modes. Neutral wind and temperature are derived from EISCAT data. Results of the two instruments are shown. The differences between the two sets of results are discussed and show that most of the discrepancy is due to the presence of vertical winds during the observations where the magnetic activity was high.
Published: 1990
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50. New phenomena observed by EISCAT during an RF ionospheric modification experiment

Author: Bo Thidé, Wlodek Kofman, B. Isham, Peter Stubbe, C. Lahoz, Tor Hagfors, and J. A. Nordling
Subjects: Physics, Coupling, business.industry, Incoherent scatter, Plasma, Condensed Matter Physics, Space charge, Ion, Computational physics, Optics, Dielectric heating, General Earth and Planetary Sciences, Landau damping, Electrical and Electronic Engineering, Ionosphere, business
Abstract: An ionospheric HF-modification experiment was carried out near Tromso, Norway, using the Max-Planck-Institut fur Aeronomie (MPI) heating facility and the EISCAT 933-MHz incoherent scatter radar (ISR). The MPI heater was normally operated at 4.04 MHz and modulated 20-s on, 40-s off. The ISR observed waves propagating parallel to B0, and chirped as well as normal plasma line observations were performed. Heater-induced plasma lines were observed only in the first 10-s integration interval, indicating a strong overshoot. These lines are unusual in that multiple simultaneous lines were observed, normally originating within one kilometer of the critical region but sometimes from lower heights, and that the frequency of the most constant line is offset some 250 kHz from the heating frequency, with the other lines occurring at greater frequency offsets. The natural, photoelectron-enhanced plasma line was not observed; however, the background plasma was diagnosed via ion line observations and comparisons to chirped observations performed at EISCAT in May 1986 indicate that increased Landau damping may be responsible for both the strong induced-line overshoot and the lack of a distinct natural line. Finally, ion power profile observations show the existence of a topside enhanced ion line at the critical density corresponding to the heater frequency. We believe this is due to strong O to Z-mode coupling parallel to B0 and a low ƒ0F2.
Published: 1990
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