95-GHZ SCATTERING BY TERRAIN AT NEAR-GRAZING INCIDENCE

This study, consisting of three complimentary topics, examines of the millimeter-wave backscattering behavior of terrain at incidence angles extending between 70 and 90 degrees, corresponding to grazing angles of 20 degrees to 0 degrees, The first topic addresses the character of the statistical variability of the radar backscattering cross section per unit area sigma(A). Based on an evaluation of an extensive data s et acquired at 95 GHz, it was determined that the Rayleigh fading mode l (which predicts that sigma(A) is exponentially distributed) provides an excellent fit to the measured data for various types of terrain co vers, including bare surfaces, grasses, trees, dry snow, and wet snow, The second topic relates to the angular variability and dynamic range of the backscattering coefficient sigma(0), particularly near grazing incidence, In this paper, we provide a summary of data reported to da te for each of several types of terrain covers, The last topic focuses on bare surfaces, A semi-empirical model for sigma(0) is presented fo r vertical (VV), horizontal (HH), and cross (HV) polarizations, The mo del parameters include the incidence angle theta, the surface relative dielectric constant epsilon, and the surface roughness kappa s, where kappa = 2 pi/lambda and s is the surface root mean square (rms) heigh t.