Research On Robust Imaging Processing Of Azimuth Multiple Phase Center SAR

Synthetic aperture radar(SAR)is capable of acquiring earth image for all-weather and all-time,which is used widely both in civil and military field.However,conventional SAR system with single channel cannot realize high resolution in azimuth and wide swath in range at the same time under the constraint of minimum antenna area.The azimuth multiple phase centers(AMPC)SAR systems operate under condition of low pulse repetition frequency(PRF)and utilize the multiple receive channels in azimuth to compensate for inefficient PRF,which can accomplish continuous imaging process of high resolution and wide swath(HRWS).This paper focuses on the signal reconstruction of AMPC SAR under imperfect condition and tries to improve the performance of reconstruction through calibrating array error efficiently and improve the robustness of signal reconstruction methods.The fundamental principle of AMPC SAR is introduced in chapter 2.The signal model and procedure of signal processing is established.Then,the paper analyses the characters of AMPC SAR signal in view of equivalent phase centers,spectrum character in azimuth and eigen value decomposition of correlation matrix.After introducing two frequently used construction methods,the simulation of processing receive signal of point target can be carried out to verify the HRWS capability of AMPC SAR systems.This chapter is the basis of improving the performance of signal reconstruction under imperfect condition.The calibration of array errors of AMPC SAR is studied in chapter 3.The signal model is modified according to array errors.Then,the effect of array errors is simulated on the basis of the modified model.It is concluded that phase errors caused by array errors are the most important factors reducing the performance of reconstruction.The paper proposes the modified antenna pattern method which can estimate the phase errors between different channels efficiently even under nonuniform sampling and low signal to noise ratio condition.Considering that the phase errors are variant in range,the signal is divided into several parts in range and the calibration is processed separately.The robust reconstruction methods of AMPC SAR are researched in chaper4.Firstly,the principle of adaptive reconstruction methods is introduced.Secondly,the errors of steering vectors,correlation matrix and distribution of signal power are analyzed.The steering vector errors include residual phase errors after calibration and magnitude errors and azimuth time delay errors.The correlation matrix errors and deviation of signal power distribution are also inevitably in real data processing.Thirdly,several robust reconstruction methods are introduced.Among these methods,the proposed adaptive method based on covariance matrix reconstruction achieves the best performance under imperfect condition.The procedure of AMPC SAR signal processing,phase error estimating methods and signal reconstruction methods proposed in this paper are verified by real data.The performance of signal reconstruction of AMPC SAR system under imperfect condition is improved.