TABLE OF CONTENTS The next sections describe the characteristics of surface clutter. In the detection of small, low-altitude aircraft, missiles, and surface targets, radar backscatter from various land and cultural features creates a more severe problem than does the backscatter from the seas. This is because land and cultural features generally have a higher reflectivity at low grazing angles than does the sea surface. This effect is mitigated somewhat in the case of airborne targets, since the Doppler shift and spectrum width of land returns are small compared with those due to aircraft velocities. MTI techniques on stationary or slowly moving radars can have high clutter rejection ratios for most land objects (Chap. 9). The discussion in the next sections applies primarily to monostatic target-detection radars.
It is difficult to give an adequate statistical distribution of the backscatter characteristics of land for the following reasons:
The statistical nature of the return from a given area cannot be related to the type of land as easily as the relatively convenient use of sea state descriptions. (Note that even the sea-state description at any time is highly subjective.)
The land backscatter amplitude distribution at low grazing angles does not usually conform to the Rayleigh distribution because of the shadowing from hills, buildings, trees, etc. Even land that is considered flat will roll by a degree or two.
The moisture content of the soil, or snow cover, can alter the back-scatter coefficient.
The derivation of a mean ( ?
