Simple masks for shadowing and highlighting in SAR images

This paper presents a simple algorithm to indicate the areas of a Synthetic Aperture Radar (SAR) image likely to be affected by radar shadow, excessive highlighting, or the opposite phenomenon, 'lowlighting'. The algorithm is not intended as a substitute for the much lengthier routines that solve the radar mapping equation, but rather as an aid to the selection of suitable areas for more detailed investigation. It is an image-processing routine applied to a suitable Digital Elevation Model (DEM) of the terrain to be imaged. In this context, the suitability of the DEM is characterized by the ratio of the vertical to horizontal sampling intervals, and sufficient information is provided to enable the suitability of a particular DEM to be evaluated. An implementation of the algorithm in the NIH Image macro language is available at the author's web site.