Research On High-precision SAR Imaging Non-ideal Factor Compensation Methods

As an active microwave sensor,Synthetic Aperture Radar(SAR)has been applied to generate two-dimensional(2D)high-resolution images day and night under all weather conditions at a long distance,which is widely used in military and civilian applications.In order to obtain high-precision images of the target scene,the radar platform is required to move linearly along the ideal track at a constant speed.However,due to the variation of situations,SAR images are always influenced by some non-ideal factors.On the one hand,result from atmospheric disturbances and the instability of platforms,radar platforms often deviate from the ideal track.On the other hand,the target point may also move irregularly in the scene,which generates errors.These non-ideal factors result in an unknown slant range error between the radar and the target,which induces the phase error in the echo data,leads to the image defocus,and severely degrades the image quality.Therefore,to obtain high-quality and well-focused images and eliminate the influence of phase errors in the echoes,it is significant to study the non-ideal factor compensation method of high-precision SAR imaging.According to these considerations,this thesis mainly focuses on the research of high-precision SAR imaging non-ideal factor compensation,including the error compensation methods for the periodic vibration of radar platform,the irregular movement of radar platform,and the irregular movement of radar platform and nonlinear movement of targets.The specific content is summarized as follows.1.To suppress paired echoes derived by the periodic vibration of radar platform in high-precision SAR imaging,a non-parametric vibration error compensation method is proposed.By constructing a modified model and introducing a non-parametric method,the vibration phase error in the echoes can be estimated directly and then the compensation function is constructed to suppress paired echoes.It has a small calculation amount and simple process steps,which avoids the complex vibration parameter estimation in traditional methods.2.To compensate for the motion error induced by the irregular movement of radar platform in high-precision SAR time-domain imaging,and considering the high computational complexity of time-domain algorithms,a compensation method of irregular movement of platform based on hybrid coordinate(HC)system is proposed.First,the interpolation operation is optimized in the process of the fast time-domain algorithms by HC grid,which improves the execution efficiency and reduces the interpolation error.Next,an approximate Fourier transform relationship between the image domain and corresponding phase history data is established under the HC grid,so the three-dimensional trajectory deviation caused by the irregular movement of radar platform can be estimated accurately by Gauss-Newton iterative optimization,which compensates for the space-variant phase error while taking into account the operational efficiency of the time domain algorithm.This method has well robustness and universality.3.To compensate for the seriously 2D space-variant phase error derived by the irregular movement of radar platform and nonlinear movement of targets,a non-linearly moving ship target space-variant phase error estimation method is proposed based on the previous method.By the backprojection imaging in the HC grid,multiple scattering regions are selected and local phase error estimation is performed.Then,after constructing the error representation model,the phase errors of all pixels in the scene are obtained by polynomial regression.Finally,the image will be compensated precisely.Simulation experiments verify the effectiveness of the proposed method.