Radar images are created by converting time delay and doppler measurements of scatterers into range and cross-range values. An imaging radar does not provide direct height measurements of scatterers. We investigate the problem of computing height information from a pair of radar images.
Elevated scatterers will appear closer in range; this phenomenon is called radar image layover. This paper investigates how the height of a scatterer can be computed from the difference in its layover between two images. First, it is shown that for any image pair taken from a constant- altitude straight-line flight path, the difference in layover is zero and therefore images are spatially coherent. Next, an expression is derived for accuracy of height estimate as a function of range resolution and the angular difference between slant planes (image planes). As the angle between the slant planes increases, the accuracy of the height estimate improves, however, bright scatterers in one image tend to fade in the other image. This tradeoff between the accuracy of height estimate and limited angular persistence of radar scatterers is discussed.
Finally, results are shown, based on Lincoln Laboratory high-resolution (0.3 meters) polarimetric SAR imagery.