Polarimetric SAR data provide more information about objects' scattering properties and they have been widely used in the research of ship detection in the ocean.In this paper

an improved notch filter method is proposed

which uses both the polarimetric scattering mechanisms and the backscattering power of the target.By devising the projection subspace of the sea

azimuth ambiguities and coherent noises

a lower coherency of all those targets in the image can be reached

thus eliminating false alarms caused by them.What's more

a power related factor

the SPAN

is added to the detector in order to separate ships that have the similar scattering mechanism as the sea.The proposed method has been applied on RADARSAT-2 Fine Quad Mode data to validate its efficiency. Comparing to Polarimetric whitening filter(PWF) and SPAN method

the proposed method shows higher detection ability with low false alarms caused by azimuth ambiguities and coherent noises.