Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.0220b&link_type=abstract
American Astronomical Society, DPS meeting #28, #02.20; Bulletin of the American Astronomical Society, Vol. 28, p.1062
Astronomy and Astrophysics
Astronomy
Scientific paper
The diffuse component of planetary radar echoes, observed in backscatter by imaging radar systems, has been taken as a measure of "small-scale" surface roughness, sometimes loosely interpreted using Mie theory for discrete spherical scatterers [e.g., Harmon and Ostro, Icarus 62, 110--128, 1985]. No satisfactory quantitative theory or experimental basis for interpreting the diffuse component has yet been discovered. Here we present preliminary results of numerical calculations showing the effects of rock shape, composition, and placement in or on a planetary regolith on the magnitude and polarization of high angle (diffuse) echoes. We use a three-dimensional (3-D) finite-difference technique to compute scattering from ideal spheres and ellipsoids and from real rocks, all of equal volume, resting on or buried partially/fully within a regolith; details of the numerical method and results from two-dimensional (2-D) simulations are described elsewhere [Wong et al., IEEE Trans APS 44, 504--514, 1996; Baron et al., Icarus 122, 383--396, 1996]. Re-analysis of the rock population data from the Viking lander sites [Moore and Keller, Reports PGGP NASA TM-4300, 160--162, 1991] indicates that "typical" dimensions for a Martian surface rock at these sites are a (length) by 0.7a (width) by 0.5a (height); dimensions of partially-buried rocks are comparable, if one assumes the total height is twice the exposed height. Digitized models of several terrestrial rocks with similar dimensions have been produced using a 3-D laser scanner. For a given incident wave polarization, the magnitude and phase of the bidirectional scattered field can be calculated over approximately three octaves of frequency in a single run. Results from two orthogonal polarizations are used to synthesize arbitrary transmitter/receiver polarization states.
Baron John Edward
Simpson Richard A.
Tyler Leonard G.
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