RADAR POLARIZATION PROPERTIES OF VOLCANIC AND PLAYA SURFACES - APPLICATIONS TO TERRESTRIAL REMOTE-SENSING AND VENUS DATA INTERPRETATION

The radar polarization properties of lava flows in Hawaii (Kilauea) an d Arizona (SP flow), and two playa surfaces (Lunar Lake, Nevada and La vic Lake, California), are compared to the predicted behaviors of theo retical scattering models. At 5.7 cm and 24 cm wavelengths, Kilauea la va flows can be modeled by a combination of facet and diffuse (dipole- like) scattering. Scattering by rock faces on the scale of the radar w avelength is proposed to account for much of the facet return. The rad ar echoes at 24-cm wavelength from SP flow are, on average, consistent with entirely diffuse scattering, but there are regions within the fl ow where circular polarization ratios exceed unity, suggesting a coher ent scattering effect. 68 cm data for the lava flows show evidence of radar penetration and volume scattering. The playa surfaces are charac terized by polarization properties which in some cases are qualitative ly. consistent with the first-order small-perturbation model, but the echoes do not closely match the predictions of this model for any reas onable dielectric constant value. These results show that it may be di fficult to construct invertible models for the polarization behavior o f some surfaces (the playas), whereas for others (the Kilauea lava flo ws) the scattering properties can be successfully modeled. The first-o rder small-perturbation model is not appropriate for inverse modeling of most terrestrial lava flows, though very smooth surfaces on Venus m ay be amenable to the use of this model High circular polarization rat ios observed for SP flow, tentatively attributed here to coherent back scatter, may be analogous to Arecibo observations of high-reflectivity areas on Venus.