CFAR Ship Detection Methods Using Compact Polarimetric SAR in a K-Wishart Distribution

Compact polarimetric target detection is currently attracting increasing interest due to the generation of synthetic aperture radar (SAR) systems. Recently, the polarimetric notch filter (PNF) has been demonstrated to be effective for ship detection in both full-polarization and compact polarization-mode SAR images. In this paper, the probability density function (PDF) and the probability of false alarms (PFA) of the PNF are derived in the K-Wishart case (where the texture obeys the gamma distribution) since K distributions are suitable for many scenes including sea clutter. The PDF and PFA are also derived in closed forms for the polarimetric whitening filter (PWF) in the K-Wishart distribution case, the performance of which is close to that of the optimal polarimetric detector. The constant false alarm rate threshold for ship detection can be obtained from the PFA via the bisection method, which allows for the automatic and adaptive implementation of ship detection in complicated sea backgrounds in practical applications. The performances of the two detectors are compared via simulated data and measured data from AIRSAR in the compact polarimetric SAR case. The results show that the detectors given are accurate, while the PWF detector is generally better than the PNF detector in the K-Wishart case of the CP SAR model.