SIMULATION OF RADAR MOUNTAIN RETURNS USING A DIGITIZED TERRAIN MODEL

The aim of the present study is to characterize mountain returns measured with a ground-based weather radar operating in a mountainous region. A computation code based on the use of a digitized terrain model is developed for calculating the areas illuminated by the radar beam. Partial and total screening effects are accounted for in the calculation. The angular and range weighting functions of the radar measurement are modeled using Gaussian approximations to give the so-called weighted illuminated areas for various sizes of the radar resolution volume. Radar measurements are compared to the computed illuminated areas in order to determine the average backscattering coefficient of partly grass-covered, partly forested mountains: 87% of the measured time-averaged mountain return variance is explained by the computed values when the 15-dB resolution volume is considered. Additional geometrical information, provided by the calculated angles of incidence, is accounted for to yield a linear sigma((dB))(0)(alpha) model relevant for the so-called 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.