Compact Polarimetric SAR Scattering Mechanism And Target Decomposition Method

Compact Polarimetric Synthetic Aperture Radar(CP-SAR)is a new research interest in synthetic aperture radar.As a special dual-polarization mode,it can obtain more comprehensive polarization information and larger imaging width than the traditional dual-polarization mode.CP decomposition is an important way to extract information from the CP-SAR data.At present,there are three different methods in CP decomposition,including the wave-dichotomy-theorem-based(WDT-based)decomposition methods,the eigenvalue-based decomposition methods and the model-based decomposition methods.However,most of the present decomposition methods for CP SAR have the problem of overestimation of volume scattering(OVS)among the urban areas,especially the obliquely oriented buildings(OOBs).Therefore,based on the CP-SAR scattering mechanism,this paper focuses on the shortcomings of existing decomposition methods,proposes an CP-SAR decomposition method based on the urban scattering mechanism,and applies this method in order to verify its effectiveness.The work in this paper is carried out specifically in the following aspects:1.Derive the target scattering vectors obtained in different CP modes(theπ/4 mode,the CTLR mode and the DCP mode)through the CP-SAR observation model and electromagnetic wave theory.From the CP Hermitian coherence matrix,the CP Stokes vector,an important tool,is obtained.At the same time,the scattering mechanisms of typical targets are analyzed by the polarization characteristic maps in the CP mode,which lays the foundation for the subsequent research on the CP decomposition method.The various decomposition methods of the current CP-SAR are summarized and concluded.2.Focusing on the problem of overestimation of the volume scattering(OVS),we analyze the geometric model to understand the influence of the orientation angle on the scattering mechanism of the urban areas.The CP-SAR urban area descriptor that can comprehensively characterize the urban areas is constructed so as to describe the scattering mechanism of the urban areas,and a new decomposition method applicable to two modes(the CTLR mode and the π/4 mode)is proposed to reduce the volume scattering component of the urban areas and avoid the confusion between the scattering mechanism of the urban areas and the natural areas.Experiments show that the proposed method can effectively reduce the volume scattering component of the urban areas and increase the double-bounce scattering component without affecting the scattering mechanism of the natural areas,thus avoiding the confusion between the urban areas and the natural areas.3.Combining the CP decomposition method based on the urban area scattering mechanism with the traditional CP Wishart unsupervised classification,we have completed the CP Wishart classification based on the urban area scattering mechanism.Meanwhile,the super-pixel segmentation method is introduced to obtain the spatial information of the pseudo-color image after the CP-SAR decomposition using the SLIC super-pixel segmentation,and the spatial information and scattering information are combined to obtain the classification results,so as to improve the classification accuracy.Experiment shows that the proposed method improves the classification accuracy by about 25% in the urban areas with small orientation angle and about 10% in the urban areas with big orientation angle,respectively.