RADIOWAVE SCATTERING FROM SURFACE AND SUBSURFACE HETEROGENEITIES

Finite-difference time-domain (FD-TD) techniques allow practical numer ical computation of radiowave scattering by a wide range of objects (e .g., rocks) on or in a planetary regolith. Numerical models are evalua ted for two-dimensional (2-D) cases in which burial depth D and object size R of a single scatterer vary and for which the separation distan ce L between two scatterers varies. A buried object typically has a si gnificantly weaker scattering response than the same object resting on the surface, although the strongest response may occur when the scatt erer is partially buried. Large objects scatter strongly and in comple x ways, but the bounds on solutions appear to be well-defined; this sh ould be useful in predicting aggregate behavior of ensembles of scatte rers. The response of closely spaced objects differs significantly fro m the response of the objects calculated separately, but the coupling decreases rapidly with separation. Two-dimensional wavelength-scale ob jects (R similar or equal to lambda(0)) separated by L greater than or equal to 15 R effectively behave as independent scatterers. Computati ons in 2-D can be adapted for three-dimensions (3-D); preliminary resu lts are consistent with measured radar backscatter cross sections for the Moon and Venus and with estimates of block population densities on the Moon. The FD-TD code generalizes to 3-D, permitting the set of ca se studies to be expanded for interpretation of data such as those fro m Magellan. (C) 1996 Academic Press, Inc.