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R.A. Simpson (Stanford University)
Echoes from the surface of Mars have been seen in more than two-thirds of over 1000 X-band radio occultations since the beginning of MGS Mapping. Although angles for quasi-specular reflection are extreme (greater than 89.5 deg), certain inferences can be drawn about surface properties in the reflecting regions. Simple topography casts shadows with horizontal dimensions more than 100 times the vertical relief. Repeatable observations of strong echoes at high southern latitudes (poleward of 60S) suggest there are locations where the surface is very smooth on virtually all scales larger than the wavelength (3.6 cm). Some of these regions are within the broad boundaries considered for the Mars-98 Lander.