A constant false alarm rate (CFAR) detector for RADARSAT-2 along-track interferometry

Canada's RADARSAT-2 synthetic aperture radar (SAR) satellite will be equipped with an experimental ground moving target indication (GMTI) mode, which makes use of the "dual-receive" capability of the RADARSAT-2 antenna to provide two apertures aligned in the along-track direction. The mode allows two SAR images to be taken under identical geometry of observation, but separated by a short time lag. One of the GMTI techniques currently being explored is based on SAR along-track interferometry (SAR ATI), which uses the magnitude-phase information of the interferogram to extract movers from stationary clutter. In this paper, an unconventional but fully automatic detection scheme, derived using a histogram approximation to the clutter joint probability density function (PDF), is proposed. The new nonparametric method permits the implementation of a constant false alarm rate (CFAR) detector without deriving a theoretical joint PDF for the clutter interferogram. A false alarm reduction technique, based on "selective" local density calculations, is also discussed. Experiments show striking improvement in reducing the number of false alarms (up to 60% reduction) over the original detector without significantly degrading its performance. The detector is shown to be robust in its ability to handle both simulated (RADARSAT- 2) and real (airborne) data. Comparison with a conventional parametric CFAR detector, derived using theoretical marginal PDFs of the magnitude and phase of the interferogram, suggests the performance superiority of the new detector.