Research On Azimuth Multichannel SAR High-Resolution Wide-Swath Imaging Technology

With the extending application of the Synthetic Aperture Radar(SAR),the demand for high resolution wide swath(HRWS)imaging is becoming more and more urgent.But due to the restriction of minimum antenna area,the high azimuth resolution and the wide swath width can't be achieved at the same time in a conventional single channel SAR system.Then the multichannel SAR technique was proposed to resolve the contradiction resulting from limitation of antenna area by increasing samples in space domain.In this paper,we focus on the single transmit azimuth multichannel(AMC)SAR and the multi-transmit AMC SAR,corresponding to the SIMO SAR and MIMO SAR system respectively.In chapter 2,we present the simulation of the signal reconstruction and imaging mechanism of single transmit AMC SAR.The signal model of single transmit AMC SAR is described and the signal feature of time domain,frequency domain and space domain is analyzed.The algorithm of reconstructing unambiguous Doppler spectrum is derived.We carried out the one-and two-dimensional simulations of single transmit AMC SAR imaging and evaluated the performance of imaging.The effect of the change of sample space and gain-phase error is also analyzed.In Chapter 3,we present the method of the separation of echoes and the technique of image processing of multi-transmit AMC SAR.The signal model of multi-transmit AMC SAR is described and we compare the simulation results of several methods for echo separation.After echo separation,the signal can be processed by the methods of single transmit AMC SAR.Finally,the simulation demonstrates feasibility of HRWS imagery for multi-transmit AMC SAR systems.In Chapter 4,we present the calibration of channel phase error and the processing of the in-situ data of single transmit AMC SAR.After channel balance,we bring up an improved orthogonal subspace(OS)method for calibration of channel phase error.The improved OS method takes antenna patterns as weight,and applies the orthogonal restriction of signal subspace and noise subspace for all Doppler bins to establish the cost function,so the channel phase error estimation which is optimal could be obtained.This method avoids the unstable problem of channel phase error estimation of the conventional OS method which uses single Doppler bin.For the land-water area,a great bias occurs in the estimation of channel phase error.We analyze the relationship between Doppler centroid and channel phase error and obtain the conclusion that Doppler centroid block estimation errors lead to channel phase estimation bias.In order to improve the precision of the Doppler centroid block estimation,this paper proposes an effective way.This paper analyses the reason of the Doppler ambiguity hop when estimating the Doppler centroid in block.According to the position of the reference baseband Doppler centroid and the block estimate of baseband Doppler centroid,the Doppler ambiguity is adjusted differently.Finally,the effectiveness of the proposed method is demonstrated by real airborne data.