Incoherent Simulator for Mars Surface Applied to the Analysis of Sharad Radar Data

SHARAD (SHAllow RADar) is a Synthetic Aperture Radar (SAR) and Altimeter provided by ASI as a Facility Instrument to NASA's 2005 Mars Reconnaissance Orbiter. Primary objective of this nadir-looking GPR instrument is to map Martian surface and subsurface up to 2 Km depth with vertical resolution of 15 m and horizontal resolution of a few hundred meters (300 m-1 Km). Within this frame, one of the SHARAD goals is to identify Mars dielectric interfaces and to interpret them in terms of the occurrence and distribution of expected materials, including water and ice. The transmitted signal is a chirp with duration of 85 microsec and bandwidth of 10 MHz around a carrier frequency of 20 MHz. The received one is the result of the combination of surface and subsurface echoes and off-nadir surface reflection (clutter), reaching the radar after nadir surface echoes thus appearing as subsurface reflections (artifacts). In order to discern surface and subsurface echoes from clutter, we developed an incoherent simulator for the surface echoes. Input data are: DEM MOLA, SHARAD ancillary data and surface scattering models (Optical geometry, Hagfors). We modeled the Mars area to be simulated with plane square facets whose dimensions are those of the MOLA data set sampling. We applied incoherent backscattering models for rough surfaces to each facet, which is characterized by a point scatterer located in its center and a normal vector. Incoherent sum of the echoes from all point scatterers located in the illuminated area generates as a result a single surface echo. The latter is calculated for each spacecraft orbital position. Output of our processor are SHARAD simulated radar data that we can visualize in order to allow to distinguish artifacts from subsurface reflectors.