Research And Implementation Of Azimuth Ambiguity Suppressing In GF-3 SAR Imaging

Spaceborne Synthetic Aperture Radar(SSAR)has a wide range of advantages,such as wide swath,high resolution and wide area target imaging,which has attracted more and more attention.The traditional single channel system is affected by the minimum area of antenna area.The imaging conditions of high resolution and wide swath can not be met at the same time.Meanwhile,sub-Nyquist sampling in azimuth causes ambiguous imaging in azimuth of SAR,resulting in the serious misjudgement of the SAR image.Multi-channel SAR can break through the limitation of the minimum antenna area,so that the high-resolution and wide swath imaging needs can be satisfied at the same time.In multi-channel spaceborne SAR systems,the key to obtaining non-fuzzy signals by imaging processing is the multichannel ambiguity resolution technology.Its ambiguity resolution performance mainly depends on the determinacy of the array configuration,the consistency of the amplitude and phase characteristics of the channel and the echo error.Aiming at above spaceborne SAR azimuth blur suppression problems,the main contents are summarized in the following three aspects: 1.Aiming at the single channel azimuth suppression of GF-3 SAR image,the azimuth ambiguity caused by azimuth undersampling is studied.The imaging algorithm of unambiguous azimuth image is recovered is recovered by the compression sensing theory,and this method is applied to a satellite borne SAR measured data.Meanwhile,the limitation of ideal filter in restraining the azimuth ambiguity of single channel SAR is analyzed,that is,the ideal filter is only suitable for small area or a reference point target.By analyzing the offset of the azimuth and distance of the main image and the blurred image on the SAR image,the block processing of the large area image is put forward,and then the splicing and imaging are carried out,which effectively avoids the deviation and mismatch between the target information and the construction filter.2.Aiming at the dual channel azimuth suppression of GF-3 SAR image,the influence of position error,time error between channels,error of attitude measurement,and the amplitude and phase error between the channels and the antenna in azimuthal equivalent phase are analyzed in detailthe.Firstly,the adaptive amplitude and phase error estimation and coarse compensation methods are introduced,and the limitation of this problem is that it doesn't exist Doppler ambioguity in azimuth.Secondly,the ambiguity suppression technology based on adaptive weights for spatial filtering is also analyzed.Finally,a channel error correction method is proposed from a coarse to fine.The first step is to extract the error fitting of the non-flat spectrum by using the wavelet filter function.According to the phase error of the dual channel signal,the correlation function is used to process the rough correction and the azimuth reconfiguration,and the second step is to define the azimuth ambiguity suppression ratio by using changes of the square of amplitude in ambiguous area.And utilizing the gradient descent method to solve it.When the azimuth suppression is no longer increased,we can finish the iteration.3.Aiming at the problems about moving target imaging position offset and defocusing in process of double channel ocean moving target detection and azimuth ambiguity suppression of GF-3 SAR image,this thesis first introduces the detection and extraction of moving target.After that,the target image entropy is minimized as the objective function to estimate the channel error algorithm.In the end,the Maximum lilelihood minimum entroy(MLME)algorithm is used to estimate the moving target.Finally,the phase gradient autofocus method is used to focus the moving target.Finally,a two channel moving target detection and fuzzy suppression technique imaging algorithm under the ocean background is proposed.