Detecting moving targets in SAR via keystoning and multiple phase center interferometry

Without motion compensation, synthetic aperture radar (SAR) images of the ground are generally blurred. In 1997, MITRE reported the development technique called the keystone process for removing the range migration caused by the radial velocity component of each pixel´s movement within the scene, whether moving or stationary with respect to the ground. When applied to multiple phase center phased array radar data, this first pass process allows for automated detection of moving targets via phase thresholding. Once detected in phase space, the moving targets can be individually and automatically focused using the procedures previously reported. Although we can easily detect and accurately geo-locate bright (large radar cross-sections) moving targets using either phase or amplitude thresholding techniques, we have found that, for smaller targets, the phase differences between the cells containing the moving target are greatly distorted by the presence of strong ground clutter simultaneously present in those cells. Only after the ground clutter is cancelled will the phase difference be sufficiently dominated by the target response to allow correct geo-positioning. Here we report on a technique whereby the clutter may be cancelled by using multiple phase centers.