Optimal Time Window Selection Algorithm For Bistatic SAR/ISAR Maritime Moving Target Imaging

Airborne bistatic synthetic aperture radar system,which sets transmitter and receiver on different platforms,is widely used because of its good concealment,anti-interference and flexibility,and plays an important role in military application,scientific research and civil field.Bistatic SAR/ISAR time-window optimization imaging algorithm refers to using the angular motion of targets,which caused by sea waves,to select the optimal imaging timewindow through the time-variability of echo Doppler information.This algorithm can achieve the desired lateral resolution imaging.Selecting the optimal imaging time window is the premise of high resolution imaging of sea moving targets.In thesis,echo modeling and characteristic analysis,timewindow optimization method research and simulation experiments are carried out around bistatic SAR/ISAR sea surface target imaging.The main contents are as follows:1.The echo signal model of bistatic SAR/ISAR moving target on sea surface is established,and the range migration characteristics of complex moving target echo under the action of sea waves are analyzed,and the Doppler characteristics of sea moving target echo are analyzed from multiple perspectives of time and space variability,which provides a theoretical basis for the key steps of time window optimization in the subsequent sea moving target imaging.2.Based on stagnation point and maximum gradient point of time-frequency curve,an optimal imaging time selection method for sea surface moving targets is proposed.According to the time-varying Doppler information of echo signal,the nonstationary characteristics of moving targets on the sea surface are analyzed by means of phase difference method.Combined with the imaging plane,the central moment of the imaging time window is determined,and the maximum contrast is used as the image quality evaluation criterion to select the length of the time window,which completed the optimal selection of the time window and clear imaging of hybrid SAR/ISAR.3.Based on Short Time Fractional Fourier Transform,the selection method of optimal imaging time window of sea surface moving target is proposed.The short-time Fr FT technique is used to extract the time-varying spectrum information,select the time period with relatively stable Doppler frequency,and obtain the best imaging time window adaptively by combining the image contrast information,which provides a solution for the high-precision imaging of sea surface moving targets.Thesis verifies the rationality and feasibility of the model and optimization method through theoretical analysis and simulation experiment.The results show that this method can achieve time-window optimization and high resolution imaging of sea surface moving targets.