Characterization of Radar Backscatter Response of Sand-Covered Surfaces at Millimeter-Wave Frequencies

Radar imaging of deserts suffers from insufficient radar backscatter at low microwave frequencies due to the low permittivity of dry sand and relatively smooth sand surface roughness. Operating at millimeter-wave (MMW) frequencies, however, rectifies this deficiency as significant radar backscatter is generated by surface and volume scattering. This is due to the fact that sand surface roughness is electrically large and signal penetration into the dry sand, which is a homogeneous mixture of air and sand particles with dimensions comparable to a fraction of a wavelength, generates considerable volume scattering. This paper investigates both surface and volume scattering from dry sand surfaces, subject to the peculiar physical properties of sand surfaces found in sand dune-covered regions. An incoherent model is proposed that characterizes the angular dependence of volume scattering from dry sand in the presence of a 1-D rippled air/sand surface. A set of indoor experiments conducted on smooth and 1-D rippled sand surfaces at Ka-band confirms that significant volume scattering is present at MMW frequencies and that the proposed model correctly captures the observed angular dependence when 1-D surface ripples are present.