Ship Detection From The Polarimetric SAR Image

Ship is the primary transportation on the sea and plays an important role in people's life and production.Therefore,monitoring the geographical locations of ships are also crucial for us to more reasonably exploit and protect sea resources.Synthetic Aperture Radar(SAR)has been widely used in earth surveillance due to its unique advantage of independence of both time and weather conditions.As one important application,ship detection using SAR data,particularly Polarimetric SAR(PolSAR)data has attracted lots of attention in recent years.Although lots of research efforts have been devoted to ship detection,ship detection is still a challenging work due to the noise effects resulted from sea surface.In order to more effectively detect ships,especially the small ships in the case of moderate/high sea state,we propose some new methods in this paper.Generally,the contributions can be summarized as follows:(1)The polarimetric features used in most dual-pol ship detectors are correlated to each other.Under this condition,some same polarimetric information included in these features may be reused.To solve this problem,we propose a new 6D(6-Dimension)po-larimetric feature vector t6D in this paper.Then,PCA(Principal Component Analysis)is adopted to extract much deeper features from t6D and construct a new 3D(3-Dimension)feature vector t6DPCA.Finally,we replace the feature vector of GP-PNFd(Dual-pol Geo-metrical Perturbation-Polarimetric Notch Filter)with t6DPCA and develop a new method GP-PNF6DPCA.Experimental results show that the proposed method can detect ships more effectively,and a series of GP-PNFPCA methods after PCA operator are also useful to detect small ships in the case of moderate/high sea state.(2)Many ship detectors only use the characterises of ship pixel to detect ships in Quad-pol SAR image,which belongs to the category of 'pixel to pixel'.Actually,the clutter pixels surrounding ship pixels also include some significant information,and can help us to detect ships.Hence,based on this fact,we propose a new scheme in this pa-per to calculate the difference information between ship pixel and its surrounding pixels.In detail,the traditional LBP(Local Binary Pattern)model is first improved for PolSAR image,and then the polarimetric covariance difference matrix[P]is constructed.(3)A new polarimetric feature PSH(Pedestal Ship Height)is derived from[C]in this paper.Then,we verify that PSH is another metric of the depolarization of target.Tak-ing advantage of this fact,two methods are proposed for removing azimuth ambiguities in this paper.The first one is developed by combining I SPAN and PSH together,the second one is constructed by improving GP-PNF(Geometrical Perturbation-Polarimetric Notch Filter).Experimental results also show that these two detectors can not only remove azimuth ambiguities,but also detect small ships.(4)Considering that the phase information is useful for ship detection,thus,we pro-pose another scheme for calculating the scattering difference between ship pixel and its surrounding pixels.Then,the complete polarimetric covariance difference matrix[CP]is constructed.Compared to[P],the phase information is obviously included in[CP].Subsequently,a ship detection method DBSP is proposed using[CP].Experimental re-sults demonstrate thatin competition with[C]and[P],[CP]can more effectively help ship detectors improve their performance.(5)Analyzing the scattering mechanisms of ship,we find that the surface scattering is one main scattering component of small ship.However,many researchers neglect this fact and avoid using the surface scattering for detecting small ships.In this paper,one ship detector called RsDVH is proposed by combining[C]and[CP]together.Experi-mental results demonstrate that RsDVH is useful for ship detection.Besides,the results also show that the way of combining[C]and[CP]has the potential to detect small ships.