Polarization in Bistatic Radar Probing of Planetary Surfaces: Application to Mars Express Data An experiment is described for obtaining radar scattering signatures of the surface of Mars by using a radio link transmitter and the Arecibo Observatory.

Spacecraft-to-ground bistatic radar provides a straightforward method for surveying planetary surfaces on scales of importance to landers and rovers. Centimeter wave- lengths, currently in use for deep-space telecommunications, interact with surface structure of similar to somewhat larger scales. For the quasi-specular component of scattering and for surfaces uniformly illuminated by monochromatic signals from an orbiting or flyby vehicle, the echo Doppler dispersion is proportional to the root mean square (rms) surface slope. When the specular condition occurs within 10� -20� of the Brewster angle, the surface dielectric constant can be derived from relative echo power measured simultaneously in orthog- onal polarizations and the Fresnel reflection laws. Cross spectra, computed from outputs of the orthogonally polarized receivers, may be used to calculate a complete description of the polarization properties of the scattered fields. Application to planetary studies requires accurate amplitude and phase