A new PolSAR ship detection metric fused by polarimetric similarity and the third eigenvalue of the coherency matrix

In this paper, we address the problem of ship detection in PolSAR image. We firstly investigate the differences of scattering mechanism between ship targets and the sea surface based on the polarimetric similarity analysis. It is shown that, the sea surface scattering is dominated by the odd bounce (denoted as r₁), while the scattering of ship targets are both dominated by the even bounce scattering (r₂) which has been widely accepted, and the line bounce scattering (r₄) which is a new find from the experiments. Based on those differences, a metric (r₂+r₄)/r₁ can be applied to distinguish ship targets from the sea surface. To further suppress the effects of sidelobes and imaging artifacts which have the same/similar scattering behaviors with ship targets, we introduce in the third eigenvalue λ₃) of the coherency matrix and obtain the metric (r₂ + r₄)λ₃/r₁. The preliminary results show that a constant false alarm rate (CFAR) ship detector based on the proposed metric can obtain promising ship detection performance.