Targets detecting in the ocean using the cross-polarized channels of fully polarimetric SAR data

摘要

Azimuth ambiguities (ghost targets) discrimination is of great interest with the development of a synthet-ic aperture radar (SAR). And the azimuth ambiguities are often mistaken as actual targets and cause false alarms. For actual targets, HV channel signals acquired by a fully polarimetric SAR are approximately equal to a VH channel in magnitude and phase, i.e., the reciprocity theorem applies, but shifted in phase about ±ʌ for the first-order azimuth ambiguities. Exploiting this physical behavior, the real part of the product of the two cross-polarized channels, i.e.()SHVSV H, hereafter calledA12r, is employed as a new parameter for a target detection at sea. Compared with other parameters, the contrast ofA12r image between a target and the surrounding sea surface will be obviously increased whenA12r image is processed by mean filtering algo-rithm. Here, in order to detect target with constant false-alarm rates (CFARs), an analytical expression for the probability density function (pdf) ofA12r is derived based on the complex Wishart-distribution. Because a value ofA12r is greater/less than 0 for real target/its azimuth ambiguities, the first-order azimuth ambiguities can be completely removed by thisA12r-based CFAR technology. Experiments accomplished over C-band RADARSAT-2 fully polarimetric imageries confirm the validity.