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2. 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

3. Possible Yardangs of Titan and Western China Reveal Winds and Surface Erosion

Author

Radebaugh, J., Lorenz, R. D., Paillou, Philippe, Farr, T. G., Department of Geological Sciences [BYU], Brigham Young University (BYU), Johns Hopkins University (JHU), ASP 2015, 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), Jet Propulsion Laboratory (JPL), and NASA-California Institute of Technology (CALTECH)

Subjects
[SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP]
Abstract

International audience; Titan, China winds/Carve elongate forms in clays/Landscape deflating.

Published
2015

4. 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

5. 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

6. 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

7. 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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8. A Fourier-based textural feature extraction procedure

Author

Stromberg, W. D and Farr, T. G

Subjects
Earth Resources And Remote Sensing
Abstract

A procedure is presented to discriminate and characterize regions of uniform image texture. The procedure utilizes textural features consisting of pixel-by-pixel estimates of the relative emphases of annular regions of the Fourier transform. The utility and derivation of the features are described through presentation of a theoretical justification of the concept followed by a heuristic extension to a real environment. Two examples are provided that validate the technique on synthetic images and demonstrate its applicability to the discrimination of geologic texture in a radar image of a tropical vegetated area.

Published
1986

9. Microwave penetration and attenuation in desert soil - A field experiment with the Shuttle Imaging Radar

Author

Farr, T. G, Elachi, C, Hartl, P, and Chowdhury, K

Subjects
Earth Resources And Remote Sensing
Abstract

Receivers buried in the Nevada desert were used with the Shuttle Imaging Radar to measure microwave attenuation as a function of soil moisture in situ. Results agree closely with laboratory measurements of attenuation and suggest that penetration of tens of centimeters in desert soils is common for L-band (1.2-GHz) radar.

Published
1986

10. Multipolarization radar images for geologic mapping and vegetation discrimination

Author

Evans, D. L, Farr, T. G, Ford, J. P, Thompson, T. W, and Werner, C. L

Subjects
Geophysics
Abstract

NASA has developed an airborne SAR that simultaneously yields image data in four linear polarizations in L-band with 10-m resolution over a swath of about 10 km. Signal data are recorded both optically and digitally and annotated in each of the channels to facilitate completely automated digital correlation. Comparison of the relative intensities of the different polarizations furnishes discriminatory mapping information. Local intensity variations in like-polarization images result from topographic effects, while strong cross polarization responses denote the effects of vegetation cover and, in some cases, possible scattering from the subsurface. In each of the areas studied, multiple polarization data led to the discrimination and mapping of unique surface unit features.

Published
1986

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