Mathematics – Logic
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p21a1310l&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P21A-1310
Mathematics
Logic
5464 Remote Sensing, 5470 Surface Materials And Properties
Scientific paper
Since 2004, the Cassini Titan RADAR Mapper instrument, a multimode microwave multiple-beam sensor has observed the surface of Titan at 13.78 GHz. This instrument can operate as a high-resolution synthetic- aperture radar (SAR) imager, profiling altimeter, scatterometer, and radiometer, the latter able to observe simultaneously with, or separately from, the active measurements. The comparison of the data collected in these different modes of operation addresses a number of compositional and geological questions. In particular, radiometry observations near closest approach provide a powerful complement to SAR reflectivity measurements, despite the difference in the resolution. Among the 23 flybys of the Cassini prime mission for which SAR measurements were performed, 14 provided observations of Titan's linear dunes. They revealed that the fields of dunes cover a large portion of Titan's surface, mainly in low-latitudes, within ± 30°. They are radar-dark and exhibit a very high emissivity (with brightness temperatures from 3 to 5 K above that of their surroundings), consistent with a smooth surface and a low dielectric constant. Yet, many questions remain relative to their composition and geometry. We will present the results of our investigation of the correlation between the radar backscatter and the brightness temperature of the dune fields that suggests that interdunes are flat and with a higher dielectric constant than the dunes. This interpretation is supported by data from scatterometry and altimetry. It also accounts for the fact that the look direction seems to have no significant importance in the identification of the dunes. Also, both the emissivity and the reflectivity of the dune fields depend on the incidence (or emission) angle and the look direction. A few dunes were observed with a variety of geometries, especially the ones at the overlap of several swaths. The backscatter properties of these dunes as a function of the look geometry are examined to provide an estimate of the dunes slopes.
Callahan Philip S.
Hayes Alexander G.
Janssen Michael A.
Le Gall A. A.
Lorenz Ralph D.
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