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2. Titan as Revealed by the Cassini Radar

Author

Lopes, R. M. C., Wall, S. D., Elachi, C., Birch, S. P. D., Corlies, P., Coustenis, A., Hayes, A. G., Hofgartner, J. D., Janssen, M. A., Kirk, R. L., LeGall, A., Lorenz, R. D., Lunine, J. I., Malaska, M. J., Mastroguiseppe, M., Mitri, G., Neish, C. D., Notarnicola, C., Paganelli, F., Paillou, P., Poggiali, V., Radebaugh, J., Rodriguez, S., Schoenfeld, A., Soderblom, J. M., Solomonidou, A., Stofan, E. R., Stiles, B. W., Tosi, F., Turtle, E. P., West, R. D., Wood, C. A., Zebker, H. A., Barnes, J. W., Casarano, D., Encrenaz, P., Farr, T., Grima, C., Hemingway, D., Karatekin, O., Lucas, A., Mitchell, K. L., Ori, G., Orosei, R., Ries, P., Riccio, D., Soderblom, L. A., and Zhang, Z.

Published
2019
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3. Geomorphological Map of the Soi Crater Region on Titan

Author

Schoenfeld, A. M., primary, Solomonidou, A., additional, Malaska, M. J., additional, Lopes, R. M. C., additional, Birch, S. P. D., additional, Le Mouélic, S., additional, Florence, M., additional, Verlander, T., additional, Wall, S. D., additional, and Elachi, C., additional

Published
2023
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4. Radar: The Cassini Titan Radar Mapper

Author

Elachi, C., Allison, M. D., Borgarelli, L., Encrenaz, P., Im, E., Janssen, M. A., Johnson, W. T. K., Kirk, R. L., Lorenz, R. D., Lunine, J. I., Muhleman, D. O., Ostro, S. J., Picardi, G., Posa, F., Rapley, C. G., Roth, L. E., Seu, R., Soderblom, L. A., Vetrella, S., Wall, S. D., Wood, C. A., Zebker, H. A., and Russell, Christopher T., editor

Published
2004
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6. The Surface of Mars: The View from the Viking 2 Lander

Author

Mutch, T. A., Grenander, S. U., Jones, K. L., Patterson, W., Arvidson, R. E., Guinness, E. A., Avrin, P., Carlston, C. E., Binder, A. B., Sagan, C., Dunham, E. W., Fox, P. L., Pieri, D. C., Huck, F. O., Rowland, C. W., Taylor, G. R., Wall, S. D., Kahn, R., Levinthal, E. C., Liebes,, S., Tucker, R. B., Morris, E. C., Pollack, J. B., Saunders, R. S., and Wolf, M. R.

Published
1976

7. Titan as Revealed by the Cassini Radar

Author

Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Lopes, R. M C, Wall, S. D, Elachi, C., Birch, S. P D, Corlies, P., Coustenis, A., Hayes, A. G, Hofgartner, J. D, Janssen, M. A, Kirk, R. L, LeGall, A., Lorenz, R. D, Lunine, J. I, Malaska, M. J, Mastroguiseppe, M., Mitri, G., Neish, C. D, Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Lopes, R. M C, Wall, S. D, Elachi, C., Birch, S. P D, Corlies, P., Coustenis, A., Hayes, A. G, Hofgartner, J. D, Janssen, M. A, Kirk, R. L, LeGall, A., Lorenz, R. D, Lunine, J. I, Malaska, M. J, Mastroguiseppe, M., Mitri, G., and Neish, C. D

Abstract

Titan was a mostly unknown world prior to the Cassini spacecraft’s arrival in July 2004. We review the major scientific advances made by Cassini’s Titan Radar Mapper (RADAR) during 13 years of Cassini’s exploration of Saturn and its moons. RADAR measurements revealed Titan’s surface geology, observed lakes and seas of mostly liquid methane in the polar regions, measured the depth of several lakes and seas, detected temporal changes on its surface, and provided key evidence that Titan contains an interior ocean. As a result of the Cassini mission, Titan has gone from an uncharted world to one that exhibits a variety of Earth-like geologic processes and surface-atmosphere interactions. Titan has also joined the ranks of “ocean worlds” along with Enceladus and Europa, which are prime targets for astrobiological research.

Published
2021

8. Spectral and emissivity analysis of the raised ramparts around Titan's northern lakes

Author

Solomonidou, A., Le Gall, A., Malaska, M. J., Birch, S. P. D., Lopes, R. M. C., Coustenis, A., Rodriguez, S., Wall, S. D., Michaelides, R. J., Nasr, M. R., Elachi, C., Hayes, A. G., Soderblom, J. M., Schoenfeld, A. M., Matsoukas, Christos, Drossar, P., Janssen, M. A., Lawrence, K. J., Witasse, O., Yates, J., Radebaugh, J., Solomonidou, A., Le Gall, A., Malaska, M. J., Birch, S. P. D., Lopes, R. M. C., Coustenis, A., Rodriguez, S., Wall, S. D., Michaelides, R. J., Nasr, M. R., Elachi, C., Hayes, A. G., Soderblom, J. M., Schoenfeld, A. M., Matsoukas, Christos, Drossar, P., Janssen, M. A., Lawrence, K. J., Witasse, O., Yates, J., and Radebaugh, J.

Abstract

Some of Titan's small northern hemisphere lakes show raised rampart features (which are distinct from raised rims), and appear as SAR-bright mound-like annuli extending away from the lake for up to tens of kilometers from the shoreline. We investigate the infrared and microwave characteristics of these features using Cassini Visual and Infrared Mapping Spectrometer (VIMS) and RADAR data. A spectral comparative analysis is performed among the lakes, their ramparts, and the surrounding regions. We overcome the profound difference in spatial resolution between VIMS and SAR data by using a method that provides overlays between the spectral images and SAR, thus enabling the correct selection of VIMS pixels. The surface properties of the selected areas are obtained using a radiative transfer analysis on the selected VIMS pixels, in addition to emissivity obtained from the RADAR in radiometry mode. Analysis of these combined and co-registered data provides constraints for the formation mechanism(s) of raised ramparts. The results show that the emissivity of the raised ramparts is close to that of Titan's labyrinthic terrains and to that of empty lake floors in the northern polar regions. This is confirmed by the VIMS analysis that also shows that the infrared spectral response of the raised ramparts is very similar to that of some empty lake floors. This suggests that both areas are made from or are covered by a similar material. In addition, two out of the eight lakes with raised ramparts show spectral differences at three specific wavelengths, 1.6, 2.0, and 5.0 mu m, between the ramparts and the surrounding terrain. We hypothesize that this could be due to some component, or mixture of components in the ramparts that is less absorbent at these specific wavelengths, or it could be an effect of different grain sizes. These observations provide first insights into the possible mechanisms leading to the formation of the raised ramparts that are discussed here., QC 20200713

Published
2020
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10. Titan's Surface from Cassini RADAR SAR and High Resolution Radiometry Data of the First Five Flybys

Author

Paganelli, F, Janssen, M. A, Stiles, B, West, R, Lorenz, R. D, Lunine, J. I, Wall, S. D, Callahan, P, Lopes, R. M, Stofan, E, Kirk, R. L, Johnson, W. T. K, Roth, L, and Elachi, C

Subjects
Communications And Radar
Abstract

The first five Titan flybys with Cassini's Synthetic Aperture RADAR (SAR) and radiometer are examined with emphasis on the calibration and interpretation of the high-resolution radiometry data acquired during the SAR mode (SAR-radiometry). Maps of the 2-cm wavelength brightness temperature are obtained coincident with the SAR swath imaging, with spatial resolution approaching 6 km. A preliminary calibration shows that brightness temperature in these maps varies from 64 to 89 K. Surface features and physical properties derived from the SAR-radiometry maps and SAR imaging are strongly correlated; in general, we find that surface features with high radar reflectivity are associated with radiometrically cold regions, while surface features with low radar reflectivity correlate with radiometrically warm regions. We examined scatterplots of the normalized radar cross-section sigma(exp o) versus brightness temperature, finding differing signatures that characterize various terrains and surface features. Implications for the physical and compositional properties of these features are discussed. The results indicate that volume scattering is important in many areas of Titan's surface, particularly Xanadu, while other areas exhibit complex brightness temperature variations consistent with variable slopes or surface material and compositional properties.

Published
2007
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12. Mapping of Titan: First Results from the Cassini RADAR

Author

Stofan, E. R, Elachi, C, Lopes, R, Lorenz, R, Kirk, R. L, Paganelli, F, Wood, C. A, Wall, S. D, Luine, J, and Soderblom, L. A

Subjects
Lunar And Planetary Science And Exploration
Abstract

Like Venus, the surface of Titan is hidden from view, with little known about its geology prior to Cassini. The first Synthetic Aperture Radar (SAR) swath across the surface of Titan has revealed a surprisingly complex surface, with few features that can be reliably identified as impact craters. More detailed reports on the results of the first radar encounter with Titan can be found in this volume.

Published
2005

13. Cassini RADAR's First Look at Titan

Author

Elachi, C, Wall, S. D, Allison, M. D, Anderson, Y, Boehmer, R, Callahan, P, Encrenaz, P, Flamini, E, Francescetti, G, and Gim, Y

Subjects
Communications And Radar
Abstract

The Cassini Titan RADAR Mapper [1] is a Ku-band (13.78 GHz,lambda = 2.17 cm) linear polarized RADAR instrument capable of operating in synthetic aperture (SAR), scatterometer, altimeter and radiometer modes. Radar observations on Titan passes Ta and T3 included rastered scatterometry, SAR, altimetry and rastered radiometry images of a full hemisphere in orthogonal linear polarizations. At this writing only the Ta data have been acquired, but data from both passes will be discussed in the presentation.

Published
2005

17. A global geomorphologic map of Saturn’s moon Titan

Author

Lopes, R. M. C., primary, Malaska, M. J., additional, Schoenfeld, A. M., additional, Solomonidou, A., additional, Birch, S. P. D., additional, Florence, M., additional, Hayes, A. G., additional, Williams, D. A., additional, Radebaugh, J., additional, Verlander, T., additional, Turtle, E. P., additional, Le Gall, A., additional, and Wall, S. D., additional

Published
2019
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18. Implementation of System Requirements Models for Space Missions

Author

Smith, David B, Wall, S. D, Baker, J. C, and Krajewski, J. A

Abstract

As a part of it restructuring of the space mission design process, the Jet Propulsion Laboratory is investigating a model-driven concept for capturing system level requirements for space missions.

Published
1998

23. SRL-1: Radar Scenes of Impact Craters

Author

Greeley, R, Blumberg, D. G, McHone, J. F, Kuzmin, R, Ivanov, B, Garvin, J, Grieve, R, and Wall, S. D

Subjects
Communications And Radar
Published
1995

25. Measurement of aerodynamic roughness using radar backscatter over vegetated surfaces

Author

Wall, S. D, Rasmussen, K. R, and Greeley, R

Subjects
Earth Resources And Remote Sensing
Abstract

The importance of the measurement of wind fields is discussed. Wind regime data can be used to infer the amount and type of wind induced (aerolian) transport of sand and dust, or to establish global circulation models, for example on other planets. Since local measurements are costly and often impossible, it is desired to infer such data from remotely sensed information. A potential mechanism for remotely inferring the wind regime by using synthetic aperture radar data to describe the roughness of the surface is described. A project to estimate the practicality of using such a mechanism is described. An experiment that extends the mechanism to vegetated sites, where the goal is to measure potential for erosion, is reported.

Published
1994

26. Toward lowering the cost of mission operations

Author

Wall, S. D and Ledbetter, K. W

Subjects
Systems Analysis
Abstract

The mission operations system is one of the more significant drivers of the cost of the mission operations and data analysis segment of missions. In large or long-lived projects, the MOS can also be a driver in total mission cost. Larger numbers of missions, together with an increasingly cost-conscious environment, dictate that future missions must more strictly control costs as they perform to their requirements. It is therefore prudent to examine the conduct of past missions for ways to conserve resources. In this paper we review inputs made to past projects' 'lessons-learned' activities, in which personnel from past projects (among other things) identified major cost drivers of MOS's and considered how economies were or might have been realized in both design and performance of their MOS. Common themes among four such reviews are summarized in an attempt to provide suggestions for cost reduction in future missions.

Published
1993

27. Measurement of surface microtopography

Author

Wall, S. D, Farr, T. G, Muller, J.-P, Lewis, P, and Leberl, F. W

Subjects
Earth Resources And Remote Sensing
Abstract

Acquisition of ground truth data for use in microwave interaction modeling requires measurement of surface roughness sampled at intervals comparable to a fraction of the microwave wavelength and extensive enough to adequately represent the statistics of a surface unit. Sub-centimetric measurement accuracy is thus required over large areas, and existing techniques are usually inadequate. A technique is discussed for acquiring the necessary photogrammetric data using twin film cameras mounted on a helicopter. In an attempt to eliminate tedious data reduction, an automated technique was applied to the helicopter photographs, and results were compared to those produced by conventional stereogrammetry. Derived root-mean-square (RMS) roughness for the same stereo-pair was 7.5 cm for the automated technique versus 6.5 cm for the manual method. The principal source of error is probably due to vegetation in the scene, which affects the automated technique but is ignored by a human operator.

Published
1991

29. Transient surface liquid in Titan’s polar regions from Cassini

Author

THE CASSINI RADAR TEAM, HAYES, A. G., AHARONSON, O., LUNINE, J.I., KIRK, R. L., ZEBKER, H. A., WYE, L. C., LORENZ, R. D., TURTLE, E. P., PAILLOU, Philippe, MITRI, G., WALL, S. D., STOFAN, E. R., MITCHELL, K. L., ELACHI, C., Division of Geological and Planetary Sciences [Pasadena], California Institute of Technology (CALTECH), Lunar and Planetary Laboratory [Tucson] (LPL), University of Arizona, US Geological Survey [Flagstaff], United States Geological Survey [Reston] (USGS), Department of Electrical Engineering [Stanford], Stanford University, Johns Hopkins University Applied Physics Laboratory [Laurel, MD] (APL), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Sciences et Technologies - Bordeaux 1, Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), and Proxemy Research Inc

Subjects
Shore, geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, [PHYS.ASTR.EP]Physics [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Atmospheric circulation, Climate oscillation, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Astronomy and Astrophysics, Atmospheric sciences, 01 natural sciences, symbols.namesake, 13. Climate action, Space and Planetary Science, Radar imaging, 0103 physical sciences, symbols, Polar, Exponential decay, Water cycle, Titan (rocket family), 010303 astronomy & astrophysics, Geology, 0105 earth and related environmental sciences
Abstract

International audience; Cassini RADAR images of Titan's south polar region acquired during southern summer contain lake features which disappear between observations. These features show a tenfold increases in backscatter cross-section between images acquired one year apart, which is inconsistent with common scattering models without invoking temporal variability. The morphologic boundaries are transient, further supporting changes in lake level. These observations are consistent with the exposure of diffusely scattering lakebeds that were previously hidden by an attenuating liquid medium. We use a two-layer model to explain backscatter variations and estimate a drop in liquid depth of approximately 1-m-per-year. On larger scales, we observe shoreline recession between ISS and RADAR images of Ontario Lacus, the largest lake in Titan's south polar region. The recession, occurring between June 2005 and July 2009, is inversely proportional to slopes estimated from altimetric profiles and the exponential decay of near-shore backscatter, consistent with a uniform reduction of 4 ± 1.3 m in lake depth.Of the potential explanations for observed surface changes, we favor evaporation and infiltration. The disappearance of dark features and the recession of Ontario's shoreline represents volatile transport in an active methane-based hydrologic cycle. Observed loss rates are compared and shown to be consistent with available global circulation models. To date, no unambiguous changes in lake level have been observed between repeat images in the north polar region, although further investigation is warranted. These observations constrain volatile flux rates in Titan's hydrologic system and demonstrate that the surface plays an active role in its evolution. Constraining these seasonal changes represents the first step toward our understanding of longer climate cycles that may determine liquid distribution on Titan over orbital time periods.

Published
2011

30. Cassini RADAR's Third and Fourth Looks at Titan

Author

Elachi, C., Wall S. D., Allison M. D., Anderson Y., Boehmer R., Callaan P., Encrenaz P., Flamini E., Franceschetti G., Gim Y., Hamilton G., Hensley S., Janssen M. A., Johnson W. T. K., Kelleher K., Kirk R. L., Lopes R. M., Lorenz R., Lunine J. I., Muhleman D. O., Orosei R., Ostro S. J., Paganelli F., Picardi G., Posa F., Roth L. E., Seu R., Shaffer S., Soderblom L. A., Stiles B., Stofan E., West R., Wood C. A., Wye L., Zebker H., Rizk B., McFarlane L., VETRELLA, SERGIO, Elachi, C., Wall, S. D., Allison, M. D., Anderson, Y., Boehmer, R., Callaan, P., Encrenaz, P., Flamini, E., Franceschetti, G., Gim, Y., Hamilton, G., Hensley, S., Janssen, M. A., Johnson, W. T. K., Kelleher, K., Kirk, R. L., Lopes, R. M., Lorenz, R., Lunine, J. I., Muhleman, D. O., Orosei, R., Ostro, S. J., Paganelli, F., Picardi, G., Posa, F., Roth, L. E., Seu, R., Shaffer, S., Soderblom, L. A., Stiles, B., Stofan, E., Vetrella, Sergio, West, R., Wood, C. A., Wye, L., Zebker, H., Rizk, B., and Mcfarlane, L.

Subjects
Radar, Cassini, Titan
Abstract

The Cassini Titan RADAR Mapper has made two close passes of Titan's southern hemisphere in 2005, discovering extensive drainage channels, embayments, and broad areas of dark dunes. Together these emphasize the relative youthfulness of the surface.

Published
2006

31. Cassini RADAR's first look at Titan

Author

Elachi C., Wall S. D., Allison M. D., Anderson Y., Boehmer R., Callahan P., Encrenaz P., Flamini E., Francescetti G., Gim Y., Hamilton G., Hensley S., Janssen M. A., Johnson W. T. K., Kelleher K., Kirk R. L., Lopes R. M., Lorenz R. D., Lunine J., Muhleman D. O., Ostro S. J., Paganelli F., Picardi G., Posa F., Roth L. E., Seu R., Shaffer S., Soderblom L. A., Stiles B., Stofan E. R., West R. A., Wood C. A., Wye L., Zebker H. A., VETRELLA, SERGIO, Elachi, C., Wall, S. D., Allison, M. D., Anderson, Y., Boehmer, R., Callahan, P., Encrenaz, P., Flamini, E., Francescetti, G., Gim, Y., Hamilton, G., Hensley, S., Janssen, M. A., Johnson, W. T. K., Kelleher, K., Kirk, R. L., Lopes, R. M., Lorenz, R. D., Lunine, J., Muhleman, D. O., Ostro, S. J., Paganelli, F., Picardi, G., Posa, F., Roth, L. E., Seu, R., Shaffer, S., Soderblom, L. A., Stiles, B., Stofan, E. R., Vetrella, Sergio, West, R. A., Wood, C. A., Wye, L., and Zebker, H. A.

Abstract

The first Cassini RADAR observations of Titan reveal a geologically complex, rather smooth and radar-bright surface. Features include multiple types that may be cryovolcanic, and radar-dark possible organic deposits, but few candidate impact craters.

Published
2005

32. Cryovolcanism on Titan: New results from Cassini RADAR and VIMS

Author

Lopes, Rosaly M. C., Kirk, Randolph L., Mitchell, Karl L., Le Gall, Alice, Barnes, Jason W., Hayes, A., Kargel, J., Wye, L., Radebaugh, J., Stofan, E. R., Janssen, M. A., Neish, Catherine D., Wall, S. D., Wood, C. A., Lunine, J.I., Malaska, M. J., Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Astrogeology Science Center [Flagstaff], United States Geological Survey [Reston] (USGS), 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), University of Idaho [Moscow, USA], Department of Astronomy [Ithaca], Cornell University [New York], Department of Hydrology and Atmospheric Sciences [University of Arizona], University of Arizona, Department of Electrical Engineering [Stanford], Stanford University, Department of Geological Sciences [BYU], Brigham Young University (BYU), Proxemy Research Inc, NASA Goddard Space Flight Center (GSFC), Planetary Science Institute [Tucson] (PSI), NASA, and Department of Hydrology and Water Resources

Subjects
Volcanism, [PHYS.ASTR.EP]Physics [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], Titan, [SDU.ASTR.IM]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Instrumentation and Methods for Astrophysic [astro-ph.IM]
Abstract

International audience; The existence of cryovolcanic features on Titan has been the subject of some controversy. Here we use observations from the Cassini RADAR, including Synthetic Aperture Radar (SAR) imaging, radiometry, and topographic data as well as compositional data from the Visible and Infrared Mapping Spectrometer (VIMS) to reexamine several putative cryovolcanic features on Titan in terms of likely processes of origin (fluvial, cryovolcanic, or other). We present evidence to support the cryovolcanic origin of features in the region formerly known as Sotra Facula, which includes the deepest pit so far found on Titan (now known as Sotra Patera), flow-like features (Mohini Fluctus), and some of the highest mountains on Titan (Doom and Erebor Montes). We interpret this region to be a cryovolcanic complex of multiple cones, craters, and flows. However, we find that some other previously supposed cryovolcanic features were likely formed by other processes. Cryovolcanism is still a possible formation mechanism for several features, including the flow-like units in Hotei Regio. We discuss implications for eruption style and composition of cryovolcanism on Titan. Our analysis shows the great value of combining data sets when interpreting Titan's geology and in particular stresses the value of RADAR stereogrammetry when combined with SAR imaging and VIMS.

Published
2013

33. Alluvial Fans on Titan Reveal Materials, Processes and Regional Conditions

Author

Radebaugh, J., Lorenz, R. D., Farr, T. G., Kirk, Randolf L., Lunine, J.I., Ventra, D., Le Gall, Alice, Lopes, R. M. C., Barnes, Jason W., Hayes, A. G., Stofan, E. R., Wall, S. D., Wood, C., Cardon, Catherine, Department of Geological Sciences [BYU], Brigham Young University (BYU), Johns Hopkins University Applied Physics Laboratory [Laurel, MD] (APL), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Astrogeology Science Center [Flagstaff], United States Geological Survey [Reston] (USGS), Department of Astronomy [Ithaca], Cornell University [New York], Utrecht University [Utrecht], 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), University of Idaho [Moscow, USA], Proxemy Research Inc, and Wheeling Jesuit University

Subjects
[PHYS.ASTR.EP] Physics [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], [PHYS.ASTR.EP]Physics [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], food and beverages, [SDU.ASTR.EP] Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], human activities
Abstract

International audience; Alluvial fans on Titan reveal vigorous fluvial processes occur or occurred, indicate a prolonged depositional history, and may illuminate climate conditions.

Published
2013

34. Titan's Plains: Global Distribution and Possible Origin

Author

Lopes, R. M., Alice Le Gall, Kirk, R. L., Kargel, J. S., Stofan, E. R., Mitchell, K. L., Antoine Lucas, Janssen, M. A., Wall, S. D., Malaska, M. J., Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), 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), Astrogeology Science Center [Flagstaff], United States Geological Survey [Reston] (USGS), University of Arizona, Proxemy Research Inc, California Institute of Technology (CALTECH), and Cardon, Catherine

Subjects
[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]
Abstract

International audience; Titan's diverse and Earth-like geologic features have been mapped and interpreted based on their morphological characteristics (Lopes et al., 2010, Icarus 205; Aharonson et al., 2012, Titan: Surface, Atmosphere, Magnetosphere, Cambridge University Press). While the interpretation for the origin of some units, such as dunes and well-preserved impact craters, has been relatively straightforward, others have been more challenging. In particular, the undifferentiated plains first mapped by Lopes et al. (2010) remain mysterious. These vast expanses, mostly found at mid-latitudes are relatively featureless and appear to have low relief. Their gradational boundaries and paucity of features in SAR data make geologic interpretation particularly difficult using only this dataset. Plains may be sedimentary in origin, resulting from fluvial or lacustrine deposition or accumulation of photolysis products created in the upper atmosphere. Alternatively, the plains may be cryovolcanic, consisting of overlapping flows of low relief, obscured by accumulation of sediments. In this paper, we use SAR, radiometry, scatterometry, and SARTopo data to examine the characteristics of the plains and compare them with other geologic units. We also compare their global distribution with that of other units and examine the implications of a possible cryovolcanic origin.

Published
2012

35. Coexistence of Dunes and Humid Conditions at Titan's Tropics

Author

Radebaugh, Jani, Lorenz, R. D., Lunine, J.I., Kirk, R. L., Ori, G. G., Farr, T. G., Malaska, M., Le Gall, Alice, Liu, Z. Y. C., Encrenaz, P. J., Paillou, Philippe, Hayes, A., Lopes, R. M. C., Turtle, E. P., Wall, S. D., Stofan, E. R., Wood, C. A., Department of Geological Sciences [BYU], Brigham Young University (BYU), Johns Hopkins University Applied Physics Laboratory [Laurel, MD] (APL), Department of Astronomy [Ithaca], Cornell University [New York], Astrogeology Science Center [Flagstaff], United States Geological Survey [Reston] (USGS), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), 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), SSE 2012, Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Bordeaux (UB), Proxemy Research Inc, Wheeling Jesuit University, Cassini Radar, Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Observatoire aquitain des sciences de l'univers (OASU), and Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB)

Subjects
[PHYS.ASTR.EP]Physics [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]
Abstract

International audience; At Titan's equatorial latitudes there are tens of thousands of dunes, a landform typical of desert environments where sand does not become anchored by vegetation or fluids. Model climate simulations predict generally dry conditions at the equator and humid conditions near the poles of Titan, where lakes of methane/ethane are found. However, moderate relative methane humidity was observed at the Huygens landing site, recent rainfall was seen by Cassini ISS near the Belet Sand Sea, and a putative transient lake in Shangri-La was observed by Cassini VIMS, all of which indicate abundant fluids may be present, at least periodically, at Titan's equatorial latitudes. Terrestrial observations and studies demonstrate dunes can exist and migrate in conditions of high humidity. Active dunes are found in humid climates, indicating the movement of sand is not always prohibited by the presence of fluids. Sand mobility is related to precipitation, evaporation and wind speed and direction. If dune surfaces become wetted by rainfall or rising subsurface fluids, they can become immobilized. However, winds can act to dry the uppermost layers, freeing sands for saltation and enabling dune migration in wet conditions. Active dunes are found in tropical NE Brazil and NE Australia, where there are alternating dry and wet periods, a condition possible for Titan's tropics. Rising and falling water levels lead to the alteration of dune forms, mainly from being anchored by vegetation, but also from cementation by carbonates or clays. Studies of Titan's dunes, which could undergo anchoring of organic sediments by hydrocarbon fluids, could inform the relative strength of vegetation vs. cementation at humid dune regions on Earth. Furthermore, a comprehensive survey of dune morphologies near regions deemed low by SARTopo and stereo, where liquids may collect in wet conditions, could reveal if bodies of liquid have recently existed at Titan's tropics.

Published
2012

36. Dune material budget and distribution on Titan using Cassini radar and radiometry observations (Invited)

Author

Janssen, M. A., Wye, L., Hayes, A. G., Lorenz, R. D., Radebaugh, J., Lunine, J.I., Kirk, R. L., Lopes, R. M., Wall, S. D., Stofan, E. R., Farr, T. G., Paillou, Philippe, Cassini Radar Team, Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Stanford University, Division of Geological and Planetary Sciences [Pasadena], California Institute of Technology (CALTECH), Johns Hopkins University Applied Physics Laboratory [Laurel, MD] (APL), Lunar and Planetary Laboratory [Tucson] (LPL), University of Arizona, US Geological Survey [Flagstaff], United States Geological Survey [Reston] (USGS), Proxemy Research Inc, SSE 2010, Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), and Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Bordeaux (UB)

Subjects
Surface materials and properties, [6281] PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS, [PHYS.ASTR.EP]Physics [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], [5470] PLANETARY SCIENCES: SOLID SURFACE PLANETS, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], [5464] PLANETARY SCIENCES: SOLID SURFACE PLANETS, Erosion and weathering, Remote sensing, [5415] PLANETARY SCIENCES: SOLID SURFACE PLANETS, Titan
Abstract

International audience; Titan's equatorial regions are covered by vast fields of longitudinal dunes. Several observations point to solid hydrocarbons as the most likely candidate for the dune particle composition. Together with the polar lakes and seas, dune regions are thus the main reservoir of organic deposits on Titan. A refined estimate of the dune material volume and distribution is essential to constrain Titan total organic inventory and therefore to understand the carbon cycle on Titan. Using Cassini SAR observations we find that Titan's dune fields are generally hosted by basins and may cover ~12.5% of Titan's surface, which corresponds to an area of ~10 million km2 (roughly the area of the United States). Polarized radiometry observations indicate that dune particles are mainly composed of organic solids, consistent with spectroscopic measurements. This would imply that the dune particles were dominantly created by atmospheric photochemical production rather than fluvial erosion. However, it is not clear whether the aggregation occurred primarily during aerosol sedimentation from the stratosphere to the surface, or by subsequent sticking and growth during fluvial or eolian transport. Assuming that, everywhere, the dunes are 100m-high and that the interdunes spaces are clear of dune material and of equal area than the dunes, the volume of sand-sized sediments should approach ~250 000 km3, which is an order of magnitude higher than the current estimate of the volume of liquid hydrocarbons on Titan (Lorenz et al., 2008). However, the combined radar and radiometry measurements indicate regional variations among the dunes. In this paper we will show that differences in the microwave backscatter and emission of the dune regions can be well explained by various degrees of exposure of the icy bedrock of Titan in the interdunal corridors. In some regions, a thick sheet of sand-sized material covers the interdunes. In other places, the original substrate is peeking through. These variations need to be taken into account in order to estimate the volume of sand-sized sediments. Investigating them also bring new insights on the distribution of the available sand-sized sediments supply, which vary across Titan probably owing to differences in the ground humidity and wind patterns.

Published
2010

37. Varied Geologic Terrains at Titan's South Pole: First Results from T39

Author

STOFAN, E. R., ELACHI, C., LUNINE, J.I., LORENZ, R. D., KIRK, R. L., LOPES, R. M. C., WOOD, C. A., RADEBAUGH, J., WALL, S. D., MITCHELL, K. L., SODERBLOM, L. A., PAILLOU, Philippe, FARR, T., STILES, B., CALLAHAN, P., CASSINI RADAR TEAM, Proxemy Research Inc, Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Lunar and Planetary Laboratory [Tucson] (LPL), University of Arizona, US Geological Survey [Flagstaff], United States Geological Survey [Reston] (USGS), Wheeling Jesuit University, Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire aquitain des sciences de l'univers (OASU), Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), and Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS.ASTR.EP]Physics [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]
Abstract

International audience; The Cassini RADAR pass T39 of the south polar region reveals extremely varied and in some cases complex surface morphologies, indicating that a range of geologic processes have operated, and are operating, in the region.

Published
2008

38. Degraded Impact Craters on Titan

Author

WOOD, C. A., LUNINE, J.I., STOFAN, E. R., LORENZ, R. D., LOPES, R. M. C., RADEBAUGH, J., WALL, S. D., PAILLOU, Philippe, FARR, T., Wheeling Jesuit University, Lunar and Planetary Laboratory [Tucson] (LPL), University of Arizona, Proxemy Research Inc, Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire aquitain des sciences de l'univers (OASU), Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), and Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS.ASTR.EP]Physics [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], ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2008

39. The north polar lakes of Titan as observed by Cassini Radar

Author

MITCHELL, K. L., PAILLOU, Philippe, KIRK, R. L., LUNINE, J.I., STOFAN, E. R., RADEBAUGH, J., WALL, S. D., HAYES, A. G., LOPES, R. M., STILES, B. W., OSTRO, S. J., LORENZ, R. D., WOOD, C. A., CASSINI RADAR TEAM, Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire aquitain des sciences de l'univers (OASU), Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Sciences et Technologies - Bordeaux 1, US Geological Survey [Flagstaff], United States Geological Survey [Reston] (USGS), Lunar and Planetary Laboratory [Tucson] (LPL), University of Arizona, Proxemy Research Inc, Division of Geological and Planetary Sciences [Pasadena], California Institute of Technology (CALTECH), Johns Hopkins University Applied Physics Laboratory [Laurel, MD] (APL), and Wheeling Jesuit University

Subjects
9345 Large bodies of water (e.g, [PHYS.ASTR.EP]Physics [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], 2419 Ion chemistry and composition (0335), 2400 IONOSPHERE (6929), lakes and inland seas) (0746)
Abstract

Over the course of a year, Cassini RADAR obtained Synthetic Aperture Radar images covering 69 percent of Titan's polar region north of 65 degrees; the region being 1.4E6 km3 in extent, greater than double the land area of the USA. We observe several hundred lakes with a range of morphological expression, including areally massive and morphologically distinctive "seas", covering ~15% of the polar region. Lakes are extremely radar dark, consistent with a lossy liquid hydrocarbon. Preliminary laboratory estimates suggest that loss tangents in the range 10E4 to 2x10E3 are reasonable, which implies that one can see through at least a few to many tens of m of liquids before the noise floor is reached, consistent with observed brightening towards many lake shores. North polar lake volumes are most likely in the 8E3 - 1.4E6 km3 range. Uncertainties will be reduced as more data, both image-based and experimental, are obtained but we can conclude with a high degree of confidence that hydrocarbon lakes on Titan are more voluminous than known terrestrial oil reserves; current estimates range from 2248 - 3896 billion barrels of oil (J. Hakes, 2000, Long Term World Oil Supply, Meeting of the Am. Ass. Pet. Geol., 18th April 2000, New Orleans, LA, http://www.eia.doe.gov/pub/oil_gas/petroleum/presentations/2000/long_term_supply.), hence 357 - 619 km3 . Small lakes often occupy steep-sided depressions, and although thermal and cryovolcanic origins cannot be completely ruled out, we are seeing growing geomorphologic evidence for dissolution chemistry, indicative of karst-like geology. The dichotomy between small lakes over slightly more than one half of the region, and seas on the other half, may be best explained by a topographic anomaly causing sub-surface flow of materials from the lakes to the seas. This may also explain observations by the Cassini ISS team (E. Turtle et al., in prep.) of a putative massive sea extending considerably further south than other observed north polar lakes.

Published
2007

40. Titan's North Polar Lakes as Observed by Cassini Radar: An Update

Author

MITCHELL, K. L., WALL, S. D., STOFAN, E. R., LOPES, R. M. C., JANSSEN, M., STILES, B., PAILLOU, Philippe, MITRI, G., LUNINE, J., OSTRO, S., LORENZ, R. D., FARR, T. G., KIRK, R. L., RADEBAUGH, J., CASSINI RADAR SCIENCE TEAM, Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Proxemy Research Inc, Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire aquitain des sciences de l'univers (OASU), Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Lunar and Planetary Laboratory [Tucson] (LPL), University of Arizona, Johns Hopkins University Applied Physics Laboratory [Laurel, MD] (APL), US Geological Survey [Flagstaff], and United States Geological Survey [Reston] (USGS)

Subjects
[PHYS.ASTR.EP]Physics [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], ComputingMilieux_MISCELLANEOUS
Abstract

International audience; Not Available

Published
2007

41. Cassini/Altimeter and Vims Complementarity: Example Using Observations Over the Same Area From Ta and T13 Titan's Flybys

Author

Crapeau, M., Rodriguez, S., Le Mouelic, S., Paillou, Philippe, Sotin, C., Wall, S. D., The Vims Science Team, The Radar Science Team, Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), Laboratoire de Planétologie et Géodynamique UMR6112 (LPG), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Nantes - Faculté des Sciences et des Techniques, Université de Nantes (UN)-Université de Nantes (UN)-Université d'Angers (UA), Observatoire aquitain des sciences de l'univers (OASU), Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Jet Propulsion Laboratory (JPL), California Institute of Technology (CALTECH)-NASA, Laboratoire de Planétologie et Géodynamique [UMR 6112] (LPG), Université d'Angers (UA)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), NASA-California Institute of Technology (CALTECH), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), and Pomies, Marie-Paule

Subjects
[PHYS.ASTR.EP] Physics [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], [SDU.STU.PL]Sciences of the Universe [physics]/Earth Sciences/Planetology, [PHYS.ASTR.EP]Physics [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], [SDU.ASTR.EP] Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], ComputingMethodologies_GENERAL
Abstract

International audience; The altimeter mode of the Ku-band RADAR experiment onboard the Cassini-Huygens mission has been designed primarily for the study of Titan's surface topography. Inspired by what is done on the Earth in icy contexts like in the Antarctic, Cassini altimetry data can also be used to retrieve the radar reflectivity of Titan's surface and thus, information about its nature. Our first study shows clear contrasts of the radar reflectivity along the altimeter track acquired during the first Titan flyby (Ta). This distinct decrease in radar reflectivity is somewhat correlated with a slight surface height variation. The 13th Titan flyby (T13) provided us VIMS (Visual and Infrared Mapping Spectrometer, operating between 0.3 and 5.1 µm) medium resolution observations of the same region. Infrared I/F along the Ta altimeter track presents a very strong correlation with the computed radar reflectivity. These correlations between infrared I/F and radar reflectivity variations indicate a change in the surface nature and the presence of a clearly defined surface structure under the track. VIMS 2.03/1.27 µm channels ratio transect along the altimeter track also suggests a local enrichment in water ice associated with a smooth depression, maybe witnessing ancient channels.

Published
2006

42. Radar: The Cassini Titan Radar Mapper

Author

Elachi, C., primary, Allison, M. D., additional, Borgarelli, L., additional, Encrenaz, P., additional, Im, E., additional, Janssen, M. A., additional, Johnson, W. T. K., additional, Kirk, R. L., additional, Lorenz, R. D., additional, Lunine, J. I., additional, Muhleman, D. O., additional, Ostro, S. J., additional, Picardi, G., additional, Posa, F., additional, Rapley, C. G., additional, Roth, L. E., additional, Seu, R., additional, Soderblom, L. A., additional, Vetrella, S., additional, Wall, S. D., additional, Wood, C. A., additional, and Zebker, H. A., additional

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43. Transient features in a Titan sea

Author

Hofgartner, J. D., primary, Hayes, A. G., additional, Lunine, J. I., additional, Zebker, H., additional, Stiles, B. W., additional, Sotin, C., additional, Barnes, J. W., additional, Turtle, E. P., additional, Baines, K. H., additional, Brown, R. H., additional, Buratti, B. J., additional, Clark, R. N., additional, Encrenaz, P., additional, Kirk, R. D., additional, Le Gall, A., additional, Lopes, R. M., additional, Lorenz, R. D., additional, Malaska, M. J., additional, Mitchell, K. L., additional, Nicholson, P. D., additional, Paillou, P., additional, Radebaugh, J., additional, Wall, S. D., additional, and Wood, C., additional

Published
2014
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44. Cassini RADAR images at Hotei Arcus and western Xanadu, Titan: Evidence for geologically recent cryovolcanic activity

Author

Wall, S. D., primary, Lopes, R. M., additional, Stofan, E. R., additional, Wood, C. A., additional, Radebaugh, J. L., additional, Hörst, S. M., additional, Stiles, B. W., additional, Nelson, R. M., additional, Kamp, L. W., additional, Janssen, M. A., additional, Lorenz, R. D., additional, Lunine, J. I., additional, Farr, T. G., additional, Mitri, G., additional, Paillou, P., additional, Paganelli, F., additional, and Mitchell, K. L., additional

Published
2009
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45. Spaceborne radar observations: A guide for Magellan radar-image analysis

Author

Ford, J. P, Blom, R. G, Crisp, J. A, Elachi, Charles, Farr, T. G, Saunders, R. Stephen, Theilig, E. E, Wall, S. D, and Yewell, S. B

Subjects
Earth Resources And Remote Sensing
Abstract

Geologic analyses of spaceborne radar images of Earth are reviewed and summarized with respect to detecting, mapping, and interpreting impact craters, volcanic landforms, eolian and subsurface features, and tectonic landforms. Interpretations are illustrated mostly with Seasat synthetic aperture radar and shuttle-imaging-radar images. Analogies are drawn for the potential interpretation of radar images of Venus, with emphasis on the effects of variation in Magellan look angle with Venusian latitude. In each landform category, differences in feature perception and interpretive capability are related to variations in imaging geometry, spatial resolution, and wavelength of the imaging radar systems. Impact craters and other radially symmetrical features may show apparent bilateral symmetry parallel to the illumination vector at low look angles. The styles of eruption and the emplacement of major and minor volcanic constructs can be interpreted from morphological features observed in images. Radar responses that are governed by small-scale surface roughness may serve to distinguish flow types, but do not provide unambiguous information. Imaging of sand dunes is rigorously constrained by specific angular relations between the illumination vector and the orientation and angle of repose of the dune faces, but is independent of radar wavelength. With a single look angle, conditions that enable shallow subsurface imaging to occur do not provide the information necessary to determine whether the radar has recorded surface or subsurface features. The topographic linearity of many tectonic landforms is enhanced on images at regional and local scales, but the detection of structural detail is a strong function of illumination direction. Nontopographic tectonic lineaments may appear in response to contrasts in small-surface roughness or dielectric constant. The breakpoint for rough surfaces will vary by about 25 percent through the Magellan viewing geometries from low to high Venusian latitudes. Examples of anomalies and system artifacts that can affect image interpretation are described.

Published
1989

46. Measurement of surface microtopography using helicopter-mounted stereo film cameras and two stereo matching techniques

Author

Wall, S. D, Farr, T. G, Muller, J.-P, Lewis, P, and Leberl, F. W

Subjects
Earth Resources And Remote Sensing
Abstract

A common problem in acquiring ground-truth data for use in microwave interaction modeling is the capture of surface roughness data that are both sampled at distances comparable to a fraction of the wavelength and extensive enough to represent the surface statistics in at least one resolution cell of the microwave remote sensor used. A technique has been developed for acquiring the necessary photogrammetric data using twin 70-mm film cameras mounted on a helicopter boom. The apparatus is described, and the accuracy with which ground surface roughness can be characterized using this device is estimated. Both standard and cross-correlation methods were used for data reduction. Stereogrammetry is compared with a completely automated image-matching technique. Dense disparity images were generated from the helicopter stereo pairs. Using interior orientation parameters supplied by the camera manufacturers, and assuming that exterior orientation parameters remain constant between control target and test field photography, an extremely dense DEM (digital elevation model) for a test field has been derived. Results are compared, and accuracy estimates are presented.

Published
1989

47. Multiple incidence angle SIR-B experiment over Argentina Mapping of forest units

Author

Cimino, J, Casey, D, Wall, S. D, Brandani, A, and Rabassa, J

Subjects
Earth Resources And Remote Sensing
Abstract

Multiple incidence angle SIR-B data of the Cordon la Grasa region of the Chubut Province of Argentina are used to discriminate various forest types by their relative brightness versus incidence angle signatures. The region consists of several species of Nothofagas which change in canopy structure with elevation, slope, and exposure. In general, the factors that appear to impact the radar response most are canopy structure, density, and ground cover (presence or absence of dead trunks and branches in particular). The results of this work indicate that (1) different forest species, and structures of a single species, may be discriminated using multiple incidence angle radar imagery and (2) it is essential to consider the variation in backscatter due to incidence angle when analyzing the comparing data collected at varying frequencies and polarizations.

Published
1986

48. Conclusion of Viking Lander Imaging Investigation: Picture catalog of experiment data record

Author

Wall, S. D and Ashmore, T. C

Subjects
Lunar And Planetary Exploration
Abstract

The images returned by the two Viking landers during the Viking Survey Mission are presented in this report. Listing of supplemental information which describe the conditions under which the images were acquired are included. Subsets of the images are listed in a variety of sequences to aid in locating images of interest. The format and organization of the digital magnetic tape storage of the images are described. A brief description of the mission and the camera system is also included.

Published
1985

49. The SIR-C experiment - Measuring new variables from space with SAR

Author

Wall, S. D

Subjects
Earth Resources And Remote Sensing
Abstract

SIR-C is a continuation of the Shuttle Imaging Radar (SIR) series of synthetic aperture radar (SAR) imaging systems flown by the Jet Propulsion Laboratory aboard the Space Shuttle. SIR-A, flown in 1981, showed that SAR can be a useful remote sensing tool in the fields of geology, hydrology, and oceanography. SIR-B added the capability of moving the radar's antenna in 1984, showing that multiple incidence angle images add materially to the usefulness of SAR. SIR-C will add the dimensions of wavelength and polarization, providing the most powerful system ever flown for SAR scientific studies of the earth.

Published
1985

50. Three Mars years - Viking Lander 1 imaging observations

Author

Arvidson, R. E, Guinness, E. A, Moore, H. J, Tillman, J, and Wall, S. D

Subjects
Lunar And Planetary Exploration
Abstract

The Mutch Memorial Station (Viking Lander 1) on Mars acquired imaging and meteorological data over a period of 2245 martian days (3.3 martian years). This article discusses the deposition and erosion of thin deposits (ten to hundreds of micrometers) of bright red dust associated with global dust storms, and the removal of centimeter amounts of material in selected areas during a dust storm late in the third winter. Atmospheric pressure data acquired during the period of intense erosion imply that baroclinic disturbances and strong diurnal solar tidal heating combined to produce strong winds. Erosion occurred principally in areas where soil cohesion was reduced by earlier surface sampler activities. Except for redistribution of thin layers of materials, the surface appears to be remarkably stable, perhaps because of cohension of the undisturbed surface material.

Published
1983

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