Research On Some Techniques Of ISAR Imaging For Space Micro-Motion Targets

Space micro-motion target is a kind of important spatial targets.With the increase of human space activities,micro-target imaging has become a hot topic because it can provide important information for targets recognition and spatial security.However,most of these targets do not meet the small rotation angle approximation for RD imaging,the existing imaging methods is difficult to achieve the ideal imaging results,so there is a need for more in-depth study.In this thesis,the imaging difficulty and imaging method are summarized on the basis of analyzing the micro-doppler and the distance-slow time echo for the particularity of the micro-moving target imaging.The time-frequency analysis instantaneous imaging method based on non-micro-motion parameters estimation is optimized.The backward projection transformation imaging method is improved from the perspective of improving the error tolerance of the fretting parameter,and it is extended to the precession rotational symmetry target.The spin target imaging method based on resampling and compression sensing is proposed from the point of view of avoiding the use of erroneous motion parameters.The main work of this thesis is as follows:1.The time-varying characteristics of micro-Doppler and distance-slow time echoes of spin and precession are studied.The difficulty of imaging is that it is difficult to compress imaging by Fourier transform directly in azimuth.According to the necessity of estimating the parameters such as the spin angle velocity,the micro-moving target imaging method is divided into the imaging method based on the non-micro-motion estimation method and the imaging method based on the micro-motion estimation method,and the processing process is briefly introduced.2.The instantaneous imaging method of spin target time-frequency analysis based on non-micro-motion parameters estimation is studied.Aiming at the problem that the instantaneous image is randomly selected when the target speed is large,we can select the image with poor image quality,and a kind of segmentation strategy is proposed.In this thesis,we study the instantaneous imaging method of spin target time-frequency analysis based on non-micro-motion parameters.By using the image contrast optimal criterion,a better target image under different time periods is obtained,and the simulation is carried out.3.The spin target imaging at angular velocity estimation error is analyzed,The backward projection transformation(BPT)based on the micro-parameters estimation is mainly manifested in the energy divergence and the false point,in addition,there will be false points when there is a grid error.Aiming at these shortcomings,a joint imaging method(GRT-BPT)combining generalized Radon transform(GRT)is proposed based on the analysis of envelope detection.The method utilizes weighted interconnection to achieve a balance between the imaging effect and the error tolerance.It is also achieved a good effect in moving to symmetrical target imaging.4.The fast spin target imaging method for estimating the error of angular velocity is studied from the point of view of improving the imaging effect under the error tolerance of the inherent fretting parameters.Based on the recursive elimination of the spin effect of the target echoes,the spin symmetric target half-period resampling method and the occlusion target interval half-period resampling method are proposed.And the accuracy of the estimation of the spin angular velocity required for resampling is analyzed,and its error tolerance is pointed out.Because of the low echo data obtained after resampling,the standard Fourier basis is improved and the compression sensing method is used.The simulation results show that it avoids the image blur problem of RD imaging directly after resampling.