Comparison of Observed and Calculated Near-Vertical Radar Ground Return Intensities and Fading Spectra

The study of ground-to-air terrain return is necessary in order to understand the functioning of radar altimeters. Radar return at vertical incidence can be considered to be composed of two components. One, whic his returned by a mirror-like action, is called the specular component. The other, termed scatter, is due to diffuse rerediation from individual scatterers on the ground. In recent work on return from angles near vertical, more attention has been given to the scatter component than many had previously assumed necessary. Procedure for Gathering Data: Two pulse radar units were used, one having a frequency of 3.8 KMC, and the other 415 MC. These will be referred to as the high and low frequency units. The transmitter and receiver were airborne and utilized the same antenna. The returned pulse train was photographed on a pulse-to-pulse basis as displayed on a scope during a run. From semi-automatic measuring of these films, frequency spectra and average power return pulses were plotted. Flight logs gave the altitude and velocity of the aircraft as well as the peak power transmitted