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

Abstract

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. Automated positioning of the detected target within the formed image is then accomplished (georegistration)We can easily detect and accurately georegister bright (large radar cross-sections) moving targets using a phase threshold technique reported herein. However, we have found that, for smaller targets, the phase differences between the cells containing the moving target can be greatly distorted by the presence of strong ground clutter. Only after the ground clutter is cancelled will the phase difference be sufficiently dominated by the target response to allow accurate geopositioning. Herein we describe one technique whereby the clutter may be cancelled by using multiple phase centers.

Detecting moving targets in multiple-channel SAR via double thresholding

“…By threshold comparisons within the intensity and the interferometric phase images, we [2,3,5] and others [4] have shown that it is possible to detect and geo-locate moving targets in the SAR. An example is shown in Figure 3.…”

“…Better results can be had if the ground return can be cancelled. Now, ideally (i.e., in the absence of system noise and moving targets) the images I 2 , I 5 and I 8 are simply phase shifted versions of each other and given the phase shifts, one image can be used to cancel another. To estimate the phase shift, we perform a least square error fit to the phase difference image.…”

Detecting and Georegistering Moving Ground Targets in Airborne QuickSAR via Keystoning and Multiple-Phase Center Interferometry

“…One such target is circled in red. Thus, the phase-interferometry image helps to indicate which detected objects in the SAR are moving objects [5][6][7]. The color anomaly may not be obvious in this highly shrunk image but is quite clear in an exploded version of the image.…”

Using a clustering technique for detection of moving targets in clutter-cancelled QuickSAR images

“…This technique creates a 'phase difference or 'phase interferometry' image by subtracting the phase of the image from one channel from the phase of the image from an adjacent channel. the phase anomaly [2,3,4] and thus readily detect the presence of moving targets in a QuickSAR image or sequence of images.…”