Low-Angle X-Band Radar Ground Clutter Spatial Amplitude Statistics

摘要

A large volume of X-band radar ground clutter measurement data was collected from many sites widely dispersed over the North American continent. This program of measurements involved a wide variety of terrain types, where at each site backscatter was recorded from all of the terrain within the field of view, through 360 degrees in azimuth and to ranges typically extending to 25 or 50km. As a result, in most of these measurements the angle of illumination of the earth's surface was usually very low, typically within a degree or so of grazing incidence, with much intermittent shadowing of low regions occurring within the field of view. This report examines the nature of low-angle radar ground clutter as it has come to be understood through analysis of this extensive base of measurements. Depression angle, that is, the angle below the horizontal at which the backscattering terrain point is observed at the radar antenna, is shown to be the principal parametric influence on clutter amplitude statistics, even for the very low angles and small (typically fractional) variations in angle that occur in surface-sited radar. This principal role of depression angle is the result of its effect on shadowing in a sea of patchy visibility and discrete or localized scattering sources. Following this understanding, a general predictive model for X-band ground clutter spatial amplitude statistics is developed based on specific computation of depression angle but on only relatively general specification of terrain type. The report goes on to illustrate how increasing information about terrain type allows more precise prediction of clutter statistics.