Another way to detect slow-moving tactical targets is by means of HRM coupled with some form of change detection between multiple images. The change detection methods are coherent change detection (CCD) and shadow detection, noncoherent change detection (NCD), video SAR, inverse SAR (ISAR) and synthetic monopulse. Each of these will be discussed but first an understanding of conventional SAR is required. Often, fast(er) moving targets and slow-moving targets and SAR maps are acquired by the same waveform as described at the end of Chapter 6. The separate target types are usually separated by filtering.