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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.

A large number of source separation algorithms have been developed using the second order statistics of the observed data and a priori knowledge of the model. Here we give a maximum likelihood solution based on the second order and higher order statistics of the data. This new algorithm is illustrated on simulated data.

A low-frequency ground penetrating radar, developed for martian subsurface sounding (Mars 96 Mission) is presented. During the preliminary campaigns, its performances have been studied by ice thickness determination on various glaciers. This radar is a pulse-compression system designed in order to limit the necessary peak power. It involves the phase modulation of the transmitted pulse by coded sequences. By moving the radar along a profile on the surface, a continuous section of the reflected energy associated with dielectric permittivity contrasts is obtained. Modulating the transmitted pulse and matched filtering the received signal provide a significant depth penetration while preserving a satisfactory range resolution. This processing is efficient even if the echo is partially shortened or if the signal is modified by differential attenuation. A multichannel filtering based on the spectral properties of the signal is then applied to the section. Experimental results of ice sounding on glaciers show that the ice-bedrock interface can be identified at depths between 30 and 120 m. >

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.

International audience; Low frequency spaceborn radar is a promising opportunity to investigate Earth subsurface in arid and polar areas and for planetary exploration. , The radar signal penetrates subsurface and the return signal is the sum of the surface clutter and the subsurface signal that is the signal of interest. In this paper, we describe the simulation of the surface clutter. This signal consists of two parts: electromagnetic waves scattered and one coherently reflected by the surface. Both components are jointly simulated using facet method and an elevation model. So, the method is applied to the Marsis radar experiment. The surface description (elevation model) is based on the Mola data while the simulation parameters are optimized using the instrument characteristics. The comparison of the real data with the simulated clutter allows discrimination of subsurface echoes. This comparison demonstrates the method efficiency and is the base for Marsis data interpretation. Some general conclusions concerning the simulations for other radars will be drawn

[1] The polar layered deposits are the largest reservoir of water on the surface of Mars. The physical properties of the ice and their spatial distribution are largely unknown. 140,000 data points from the sounding radar SHARAD on the Mars Reconnaissance Orbiter were analyzed over the Gemina Lingula region, one-fourth of the north polar layered deposits area. Maps of the dielectric properties of the bulk ice were drawn up. There is no basal melting signature. A drop of the dielectric constant in north-west of Gemina Lingula could be explained by an abrupt 250-meter uplift of the base. The bulk ice of the studied region has an average dielectric constant of 3.10 (σ = 0.12) and a loss tangent

International audience; This paper deals with the reconstruction of three-dimensional targets from experimental multiple-frequency data measured in the anechoic chamber of the Institut Fresnel (Marseille, France). An inverse iterative scheme is implemented with an adequate choice of the cost functional. Indeed, a Bayesian approach is considered in order to take into account the random noise which is present in the experiment. This leads to the definition of an adequate cost functional, where the weighting coefficients are changing with the frequency, the incidence angle and the receiving angle. The inversion scheme turns out to be more robust and accurate.

International audience

The Mars advanced radar for subsurface and ionospheric sounding (MARSIS) on Mars Express is the first high-frequency sounding radar operating from orbital altitudes since the Apollo 17 Lunar Sounder flown in 1972. The radar operates from a highly elliptical orbit but acquires data only from altitudes lower than 1200 km. The periapsis altitude is 250 km. This radar has been succesfully operating since August 2005. The radar is a dual channel low-frequency sounder, operates between 1.3 and 5.5 MHz (MegaHertz) with wavelengths between 230 and 55 m in free space for subsurface sounding and between 0.1 and 5.5 MHz (wavelengths between 3000 and 55 m) for ionospheric sounding. The subsurface sounder can operate at one or two-frequency bands out of four available bands at either like or cross polarization. The subsurface sounding radar transmits radio frequency (RF) pulses of 250 μs duration through a 40 m dipole antenna. The return echoes are then converted to digital form and temporarily stored on board for some digital processing. A second antenna, a monopole, provides reception for the cross-polarized return and its data are processed by a second channel. This processing reduces the data rate produced by the instrument to rates allowed by the spacecraft communications channel. These processed returns are then sent to Earth by the telecommunications system on the spacecraft. The advances in digital data acquisition and processing, since 1972, have enabled this technique to be used in a compact spacecraft science instrument.. This sounder has obtained returns from several kilometers below the surface of the Mars. The ionospheric sounder operates at altitudes greater than 800 km in a mode that sweeps the entire 0.1–5.5 MHz range. During ionospheric sounding, the transmitter sends a 91 μs tone at 127 pulses per second rate. The frequency sweep takes 7.3 s to complete the 0.1–5.5 MHz range. Operational aspects of the instrument are described, including the selection of frequency bands and receive antenna selection, which are based on the expected solar zenith angle. The process of data take planning as well as data archiving are described. Results of both subsurface and ionospheric sounding are presented.

Comet nuclei have a low density ( 500 kg.m-3, e.g. [1]) and are easily disrupted. In situ studies have unveiled surface features hinting at a pervasive internal layered structure on 9P/Tempel 1 [2]. This indicates that specific processes occurred during its formation and lifetime. Our simulations describe the internal structure of comet nuclei due to their formation as aggregates of cometesimals [3]. The simulations take into account the amount of kinetic energy dissipated by sintering processes, the ejection of material during the impact and the variation in density and sizes of the cometesimals. From 10000 to 100000 cometesimals are considered with sizes down to tens of meters. A cohesive strength and density layering of the material occurs, leading to a highly cohesive core with less cohesive outer layers. The thickness of such layers is comparable to the larger layers observed at 9P/Tempel 1 ( 200 m). The porosity also increases with the distance to the centre of the nucleus. The cohesive strength of the nuclei obtained (

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.

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.

P33B-1465; Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) is a low frequency radar. The MARSIS wavelength is about 50-100 m. These radar waves penetrate deeply in the Martian ground and the first radar echo is due to few tens meters of the surface. The amplitude of this surface echo provides useful information on the shallow subsurface. Using MARSIS radar data, we extract the reflectivity of the Martian surface from the radargrams and then we build a global radar reflectivity map. We will describe our method for the extraction and the calibration of the reflectivity. In this calibration, we correct the absorption due to the two-way of radar waves through the Martian ionosphere and compensate the surface roughness effect. The surface roughness effect is estimated by simulating the radar surface returns for each MARSIS orbit. Finally, we will present a reflectivity map without roughness effect and discuss the reflectivity variations due to change in the dielectric constant.

International audience; The Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) onboard the ROSETTA mission will probe the nucleus of comet 67P/Churyumov-Gerasimenko in 2014. The variations in signal attenuations to be observed in the 90 MHz-radar tomographies is expected to depend mainly on the three-dimensional variations of the dielectrical properties of the cometary material as a function of porosity, temperature, and mineralogical composition. To explore the parametric space associated with the variations of these parameters and their impacts on the observed dielectrical properties inverted from the CONSERT data, we use the current state of knowledge from the observations made by Tempel-1 and Hayabusa to develop parametric dielectric models of possible internal structures of 67P/C-G. The first model reflects the layered-pile structure proposed by Belton et al. (2007), and the second reflects the rubble-pile model proposed by Weissman et al. (1986). The relative complex dielectric permittivities assigned to each dielectric model are based on laboratory measurements of chondrite dust/water ice mixtures, and are varied as a function of dust fraction, porosity and temperature. For the layered pile model, where porosity is assumed constant at the level of 70% and temperature 20m below the surface is 40 K, the dielectric constant varies mainly as a function of dust fraction, ranging between 4.386-i0.0121 in the pure surface dust mantle to 2.081-i0.000182 in one of the inner ice-rich layers. The modeled dielectric permittivities are consistent with the expected deep penetration of the CONSERT wave through the nucleus. Preliminary results suggest that the changes in the physical properties of the nucleus induce substantial variation in the dielectric properties of cometary material that can be identified in the radar tomography.

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.

Introduction: The southern residual ice cap on Mars has been observed for more than a century. Thermal data from Viking indicate a dominantly CO2 composition. Infrared spectral mapping from Mars Express Orbiter has detected CO2-ice in bright areas and H2O ice darker areas. Mars Global Surveyor Mars Orbiter Camera images show that there are two distinct layered units, an older unit ( 10 m thick) and a younger unit (few meters). Those CO2 layers (8-15 meter total thickness) overlap H2O-ice rich layers. From reflectivity maps at 3, 4 and 5 MHz (i.e. 100 - 75 meters wavelength) obtained with the MARSIS radar [5], it appears clearly that the reflectivity is weaker in the residual cap region than the rest of south polar layered deposits. To understand this phenomenon, we use a simple model of reflectivity with three layers (atmosphere, CO2 ice and H2O ice). Next, we statistically estimate the MARSIS reflectivity decrease between a reference region (only H2O layer+atm ) and the southern residual cap. This comparison gives us an estimation of southern residual cap thickness and dielectric constant. Finally we discuss the uncertainties and validity of our approach. Reflectivity model of a layered medium: As the thickness of residual cap is of the order of 10 meters and as MARSIS wavelength is between 60 to 160 meters (in vacuum medium) is unresolved, but its has an impact surface reflectivity. Our reflectivity model is composed by three plane overlapping layers. We consider a medium without losses. The two free parameters of our model are the thickness and the dielectric constant of southern residual cap. The first layer is atmosphere (semi-infinite, dielectric constant equals to 1), the second layer is the residual cap considered as a pure CO2-ice layer (height : h, dielectric constant between 1.4 and 2.4) and the third layer is a pure H2O-ice layer (semi-infinite, dielectric constant equals to 3.15). As the porosity and dust content of CO2 ice is unknown, the dielectric constant can vary from 1.4 (CO2 powder) to 2.4 ( dielectric constant of bulk dry ice is 2.12). From this simple model of multilayered medium, it appears that some thickness of CO2 layer can imply a reflectivity decrease of about 2 orders of magnitude. The CO2 thickness for minimum reflectivity changes with frequency. Consequently, additional constrains on our model were obtained by using surface reflectivity in 3 MARSIS bands. Southern residual cap reflectivity by MARSIS: We have extracted MARSIS surface echoes located in the southern residual cap for the three bands centered at 3, 4 and 5 MHz. To define residual cap region, we use a Martian geologic map. Since the MARSIS data are not calibrated yet, we had to defined a reference region, where we know a priori the surface composition. This reference region corresponds to a very flat area in the south polar-layered deposits (latitude = [-81° ,-85° ], longitude = [180° , 205° ]), where we assume the composition to be pure water ice. we can compare the reflectivity distribution in the southern residual cap with regard to our reference region. Each distribution fairly matches a Gaussian distribution. Peak centers were them estimated by a Gaussian fit to the data. The estimated reflectivity decrease between residual cap and reference at 5, 4 and 3 MHz, are of 6.2, 7.4 and 8.6 dB respectively. Conclusion and perspectives: As discussed before, we have tentatively tried to understand radar reflectivity of residual cap using a reflectivity model. The best parameters found by a least square minimization method are : residual cap thickness of 14 m and residual cap dielectric constant of 2.1 (with water ice dielectric constant fixed at 3.15). This values are in good agreement with previous estimation. Although the ice cap was treated globally here, we are developing a more local approach to study geographic variations of the CO2 slab thickness with the south polar cap. This work shows the capabilities of MARSIS to look at features much lower than its wavelength. Similarly, the SHARAD radar may be sensitive to a few meter thick CO2 slab, and may be used to track seasonal variation in CO2 deposition on the south pole of Mars.

International audience

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].

This is the publishers version/PDF (Published in Annales Geophysicae, An Open Access Journal of the European Geosciences Union) Lower-thermospheric winds at high latitudes during moderately-disturbed geomagnetic conditions were studied using data obtained with the European Incoherent Scatter (EISCAT) Kiruna-Sodankylä-Tromsø (KST) ultrahigh frequency (UHF) radar system on 9–10 September 2004. The antenna-beam configuration was newly designed to minimize the estimated measurement error of the vertical neutralwind speed in the lower thermosphere. This method was also available to estimate the meridional and zonal components. The vertical neutral-wind speed at 109 km, 114 km, and 120 km heights showed large upward motions in excess of 30ms−1 in association with an ionospheric heating event. Large downward speeds in excess of −30ms−1 were also observed before and after the heating event. The meridional neutral-wind speed suddenly changed its direction from equatorward to poleward when the heating event began, and then returned equatorward coinciding with a decrease in the heating event. The magnetometer data from northern Scandinavia suggested that the center of the heated region was located about 80 km equatorward of Tromsø. The pressure gradient caused the lower-thermospheric wind to accelerate obliquely upward over Tromsø in the poleward direction. Acceleration of the neutral wind flowing on a vertically tilted isobar produced vertical wind speeds larger by more than two orders of magnitude than previously predicted, but still an order of magnitude smaller than observed speeds.

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.

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.

This paper is the first of a pair of reviews on the work done to date on E region electron temperatures at high latitudes. The present paper focuses on observations, which are based primarily on incoherent scatter radar data. We show that the emerging picture is one for which the electron temperature response is correlated with the magnitude of dc electric fields and inversely correlated to the ambient electron density. Higher resolution studies also show that departures from the average picture may be of great importance, as the electron temperature profile itself can vary, the magnitude of the temperatures can change substantially on a scale of a minute or less, and the correlations with electric fields and electron densities may be blurred. We show that the behaviour of the electron temperature is related to that of plasma irregularities, which has implications for the understanding of coherent radar echoes.

The Martian ionosphere's local total electron content (TEC) and the neutral atmosphere scale height can be derived from radar echoes reflected from the surface of the planet. We report the global distribution of the TEC by analyzing more than 750,000 echoes of the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). This is the first direct measurement of the TEC of the Martian ionosphere. The technique used in this paper is a novel 'transmission-mode' sounding of the ionosphere of Mars in contrast to the Active Ionospheric Sounding experiment (AIS) on MARSIS, which generally operates in the reflection mode. This technique yields a global map of the TEC for the Martian ionosphere. The radar transmits a wideband chirp signal that travels through the ionosphere before and after being reflected from the surface. The received waves are attenuated, delayed and dispersed, depending on the electron density in the column directly below the spacecraft. In the process of correcting the radar signal, we are able to estimate the TEC and its global distribution with an unprecedented resolution of about 0.1 deg in latitude (5 km footprint). The mapping of the relative geographical variations in the estimated nightside TEC data reveals an intricate web of high electron density regions that correspond to regions where crustal magnetic field lines are connected to the solar wind. Our data demonstrates that these regions are generally but not exclusively associated with areas that have magnetic field lines perpendicular to the surface of Mars. As a result, the global TEC map provides a high-resolution view of where the Martian crustal magnetic field is connected to the solar wind. We also provide an estimate of the neutral atmospheric scale height near the ionospheric peak and observe temporal fluctuations in peak electron density related to solar activity.

International audience

EPSC2007-A-00544

International audience; This presentation will be about the overall science performance and results of the shallow radar SHARAD on the MRO mission.

EGU2007-A-07887

EGU2007-A-06650; For more than three years SPICAM UV spectrometer onboard ESA mission Mars Express has been successfully monitoring the upper atmosphere of Mars in the range 118-320 nm. We will present the preliminary results concerning the numerical modelling of Mars' dayglow through the computation of UV emission lines such as CO Cameron bands and N2 Vegard-aplan bands. The theory underlying this modelling uses Boltzmann's statistical kinetic and fluid approaches to yield electron/ion density and temperature profiles as a function of altitude as well as observable variables like the volume emission rates. The outputs of the model can be directly compared to the processed SPICAM data. A few characteristic orbits are then chosen for analysis in order to compare with the numerical modelling.

The ice-rich south polar layered deposits of Mars were probed with the Mars Advanced Radar for Subsurface and Ionospheric Sounding on the Mars Express orbiter. The radar signals penetrate deep into the deposits (more than 3.7 kilometers). For most of the area, a reflection is detected at a time delay that is consistent with an interface between the deposits and the substrate. The reflected power from this interface indicates minimal attenuation of the signal, suggesting a composition of nearly pure water ice. Maps were generated of the topography of the basal interface and the thickness of the layered deposits. A set of buried depressions is seen within 300 kilometers of the pole. The thickness map shows an asymmetric distribution of the deposits and regions of anomalous thickness. The total volume is estimated to be 1.6 × 10 6 cubic kilometers, which is equivalent to a global water layer approximately 11 meters thick.

P11B-0540; We investigate the inverse problem of imaging the internal structure of comet 67P/Churyumov-Gerasimenko from radiotomography CONSERT data (radiowave transmitted back and forth from the Rosetta orbiter to the Philae lander through the comet) by using grid computing techniques. For this purpose we use a massively parallel approach based on the discretization of the interior dielectric permittivity and of the shape of the comet, as well as the interior /exterior electric field, along suitable basis of spectral functions, in the frame of the Helmholtz equation.

The primary scientific goal of the CONSERT experiment on the Rosetta space mission is to investigate the deep interior of the nucleus of comet 67/P Churyumov-Gerasimenko. This will be achieved through the use of long wavelength radio-waves, transmitted from the orbiter and returned from the lander. In this overview, a description of the instrument is presented together with a brief description of the experiment. Some important results from the tests carried out during the commissioning phase and results from a trial run in the French Alps on the temperate glacier near Argentiere are also described. During these latter tests we installed the CONSERT Lander in a tunnel under the glacier while the CONSERT Orbiter was moved along the surface. The signals received showed that the experiment is working satisfactorily. References are also provided to articles that contain a more detailed description of the instrument capabilities and in-depth analysis of the potential scientific outcome.

EPSC2007-A-00198

P14B-01 INVITED; International audience; The radar techniques are widely used in the planetary exploration to map the surfaces. The observations from Earth or from spacecrafts were developed during the last decades. However, the idea to use this technique to study the subsurface started to develop during the last 10-15 years. The ability of the radio waves to penetrate the ice, permafrost and arid surface was at the origins of the development of the Ground Penetrating Radars (GPR) with a large number of the scientific work and industrial applications on Earth. The measurements from the surface can not replace the global mapping from orbiting platforms. In this presentation, on the example of MARSIS radar on the Mars Express mission measurements we evaluate the general capabilities of radar sounders for planetary exploration. The CONSERT is the experiment on board of the ROSETTA mission that will provide information about the deep interior of the comet (Kofman et al, 1998, 2007). The CONSERT instrument is an original concept of spaceborne transmission radar based on the propagation throughout the nucleus while the classical radars are based on the reflection. In this experiment, an electromagnetic signal is transmitted between the lander, located on the comet surface, and the orbiter. The transmitted signal will be measured as a function of time and as a function of the relative position of the orbiter and the lander for a number of orbits. Any signal that has propagated through the medium contains information concerning this medium. With a sufficient number of orbits one will be able to obtain many cuts of the interior of the comet and therefore to build up a tomographic image of the interior. On the CONSERT experiment example we discuss the main advantages and difficulties of the techniques using radiowaves to study the interior of asteroids and comets. The capacity of radar technique to do the tomography of the interior of the asteroids and comets is emphasized.

International audience; Mars' polar regions are covered with ice-rich layered deposits that potentially contain a record of climate variations. The sounding radar SHARAD on the Mars Reconnaissance Orbiter mapped detailed subsurface stratigraphy in the Promethei Lingula region of the south polar plateau, Planum Australe. Radar reflections interpreted as layers are correlated across adjacent orbits and are continuous for up to 150 kilometers along spacecraft orbital tracks. The reflectors are often separated into discrete reflector sequences, and strong echoes are seen as deep as 1 kilometer. In some cases, the sequences are dipping with respect to each other, suggesting an interdepositional period of erosion. In Australe Sulci, layers are exhumed, indicating recent erosion.

International audience

EGU06-A-06659; The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on the Mars Express orbiter obtained data over the North Polar Layered Deposits (NPLD)and found that they were easily penetrated to their base by the radar signal, and that the deposits must be nearly pure ice. In addition, there was no evidence for deflection of the lower contact of the NPLD with the substrate, implying a thick elastic lithosphere beneath that sector of the NPLD. Here we report on new MARSIS observations of the South Polar Layered Deposits (SPLD). The radar echoes from the surface of the SPLD are typically comparable in strength or weaker than those from surrounding smooth Mars surfaces. The signals clearly penetrate deep into the deposits at all frequency bands. In most cases, a strong reflection is seen at a time delay consistent with the expected depth of the contact of the SPLD materials with the substrate, as observed on the NPLD. Over the highest elevation SPLD surfaces, near 0° longitude, the estimated depth to the lower interface is about 3 km. In some areas, the lower interface is not clearly detected. Multiple internal interfaces are common. These can be quite continuous, over several 100 km in many cases. Some internal interfaces are substantially brighter than others, and some differences are seen in the apparent internal structure at different MARSIS frequencies. Certain regions observed multiple times consistently show a strong local brightening of the echo from the lower interface. Many areas show a gradual, rather than abrupt, decline in echo strength at time delays beyond the lower interface. Thin layered units off the main SPLD are also penetrated by MARSIS, with a second interface detected at their lower boundaries.

International audience; We use MARSIS subsurface data to derive Mars ionosphere's total electron content (TEC). Our estimation technique provides a high resolution behavior of TEC versus solar zenith angle and shows potential dependence of the TEC on local Mars magnetic field.

sous la direction de Jean Lilensten

P13D-06; The polar layered deposits of Mars are ice-rich, finely stratified materials that may provide information on the climate history of the planet. The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on the Mars Express orbiter obtained data over the North Polar Layered Deposits (NPLD) and found that they were easily penetrated to their base by the radar signal, and that the deposits must be nearly pure ice. This paper presents MARSIS observations of the South Polar Layered Deposits (SPLD) and surrounding terrain. MARSIS is a multi-frequency synthetic aperture orbital sounding radar. In its subsurface modes, MARSIS operates in four frequency bands between 1.3 and 5.5 MHz. The radar echoes from the surface of the SPLD are typically comparable in strength or weaker than those from surrounding smooth Mars surfaces. The signals clearly penetrate deep into the deposits at all frequency bands. In most cases, a strong reflection is seen at a time delay consistent with the expected depth of the contact of the SPLD materials with the substrate. Over the highest elevation SPLD surfaces, near 0° longitude, the estimated depth to the lower interface is over 3 km. In some areas, the lower interface is not clearly detected. Multiple internal reflectors are common. These can be quite continuous, over several 100 km in many cases. Some internal reflectors are substantially brighter than others, and some differences are seen in the apparent internal structure at different MARSIS frequencies. Thin (100s of m) layered units off the main SPLD are also penetrated by MARSIS, with a second interface detected at their lower boundaries. These units sometimes extend up to 1000 km northward from the SPLD. Their distribution roughly coincides with the unit mapped as the Hesperian aged "Dorsa Argentea" formation. Below the SPLD, the deep lower interfaces are interpreted as the base of the ice-rich unit, in contact with a relatively ice-poor substrate. The strong reflection from the lower interface implies very low loss and indicates that the bulk of the SPLD material is likely to be fairly pure ice, with dust fractions of probably only a few percent. The MARSIS data of the SPLD provide the opportunity to estimate the three-dimensional shape of the deposit. This allows for a new estimate of the water inventory of the SPLD, as well as further examination of effects of the overburden on the martian lithosphere.

EGU05-A-10541; The Huygens probe carried a Radar altimeter as a part of its engineering system to determine the distance to the surface of Titan during the descent. Scientific data from this instrument was received and processed by the HASI instrument. During the descent the first surface signal was received at an altitude of 45km. This signal has been analysed to determine the topography and the scattering properties of the surface of Titan along the ground track traversed during the descent. The first results of this analysis will be presented and the limitations and the accuracy of the measurements will be discussed together with the geophysical implications.

The adaptative filter for real time noise cancelling applications is shown. The signal is corrupted by an additive noise which is a linear transformation of the noise "source" available as a reference input. To obtain the disturbing noise it is necessary to estimate this transformation. The difference between the input and the estimated noise gives an estimation of the signal. The system presented here is an open loop filter which is a different case from that proposed by Widrow. The theoretical study of the performance of the system (in the case where the disturbing noise is a non stationary process) is shown. To check the stationarity of the process we introduce a criterion which conpare the estimated transformation with the previous one (learning process) and decide if it is necessary or not to change the last estimated transformation. We studied typical cases of non stationarity as change of the power of the disturbing noise or in the impulse response of the linear system. The theoretical and computer calculated results are shown. We find a good agreement between the two approaches.

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