Modelling SAR clutter in multi-resolution radar systems

The probability distribution function (pdf) used to model Synthetic Aperture Radar (SAR) clutter is an important design element in Constant False Alarm Rate (CFAR) detection; the mean of the local CFAR window is taken as the first moment of the pdf. This study presents research examining the relationship between clutter statistics and radar resolution cell size in the Convair-580 (CV-580) C-SAR and RADARSAT-2 systems. The experiment consisted of decreasing the resolution of a HV polarized, high-resolution, CV-580 sea SAR image and determining the best fit pdf for the corresponding clutter. The same methodology was used on standard- and fine-beam-mode RADARSAT-2 HV images. It was found that the G Gamma pdf could be fitted very well to the experimental data for all CV-580 and RADARSAT-2 resolutions. Furthermore, the highest resolution SAR data was Weibull distributed, and decidedly non-Gaussian, in all cases. The medium resolution CV-580 image was very closely modelled by the Lognormal distribution while the Rayleigh distribution (Gaussian statistics) proved highly suitable for modelling the lowest resolution SAR data. The test results presented in this paper may be useful to SAR researchers.