Efficient calculation in the map domain of SAR layover and shadow masks

Layover and shadow are two phenomena common in synthetic aperture radar imagery of steep terrain areas. While little can be done to mitigate backscatter estimates in layover or shadow areas, a mask is often required to exclude them from any backscatter based analysis. This paper presents an algorithm for detecting both shadow and layover areas directly in the map domain rather than converting to the slant range image domain (and back) to effect the calculation. Furthermore the algorithm presented uses a straightforward search through the map image and thus avoids the complex and inherently inefficient buffering required to search along lines of constant azimuth. As the method can be considerably simplified by assuming a constant bearing to the satellite and constant local incident angle to the local geoid, an analysis of the errors produced by making these assumptions is given. Results show that the differences are insignificant for many applications of satellite data. For aircraft SAR imagery, it is not practical to assume a constant incidence angle. However, interpolation of incidence angle has been found to give adequate results for aircraft SAR.