Wavefront Feature Extraction For SAR Target Recognization

Synthetic Aperture Radar(SAR)is an imaging system operating in the microwave band.It has all-weather,all-weather,multi-view,high-resolution features and it has immeasurable application value in national defense,military,environment and disasters.The SAR target feature extraction is the key technology for SAR target recognition.The existing SAR target features mainly focuses on the texture feature,geometric feature,polarization feature,electromagnetic scattering feature of targets.They mainly utilize the amplitude information of the target in spite of the phase information.However,feature extraction based on amplitude information may cause target information to be hidden or even lost during the imaging process.Therefore,we propose a new target feature as a supplementary feature.Inspired by the concept of wavefront in optics domain,we define the two-dimensional continuous phase surface formed by the target in the distance direction and the azimuth direction as the target's "wavefront".Zernike polynomials are utilized to approximate the SAR wavefront.Then,the coefficients of Zernike polynomials are regarded as a new feature for supporting SAR target recognition.In this paper,the quadri-wave lateral shearing interferometer(QWLSI)is used to obtain the SAR target wavefront feature.Firstly,the winding differential wavefront in the X and Y directions are obtained by shearing interference.The wrapping differential phase is developed by the branching method.Finally,the differential Zernike polynomial coefficient is obtained by approximating the target wavefront by the least squares method.Then,the coefficients are regarded as a new SAR target feature.Moreover,an experiment is carried out to prove that this feature is effective.With reference to the SAR principle,the echoes and SAR images of the scattering point targets are obtained by simulation,then the wavefront features are extracted by using the method.Further,we using the SAR data obtained in practice to extract the target wavefront features.The innovation of this paper is to focus on the phase information of SAR target,define the concept of wavefront of SAR target and utilize the quadri-wave lateral shearing interferometer to extract the target wavefront feature as a new feature of SAR target.It enriching the SAR target feature system.