SIMULATION OF RADAR MOUNTAIN RETURNS USING A DIGITIZED TERRAIN MODEL

The aim of the present study is to characterize mountain returns measu red with a ground-based weather radar operating in a mountainous regio n. A computation code based on the use of a digitized terrain model is developed for calculating the areas illuminated by the radar beam. Pa rtial and total screening effects are accounted for in the calculation . The angular and range weighting functions of the radar measurement a re modeled using Gaussian approximations to give the so-called weighte d illuminated areas for various sizes of the radar resolution volume. Radar measurements are compared to the computed illuminated areas in o rder to determine the average backscattering coefficient of partly gra ss-covered, partly forested mountains: 87% of the measured time-averag ed mountain return variance is explained by the computed values when t he 15-dB resolution volume is considered. Additional geometrical infor mation, provided by the calculated angles of incidence, is accounted f or to yield a linear sigma((dB))(0)(alpha) model relevant for the so-c alled near-grazing region since most of the angles of incidence are in the 70 degrees-90 degrees range. Here 92% of the measurement variance is explained when the sigma((dB))(0)(alpha) model is used.