Research On Azimuth-Ambiguity Free Imaging Technologies Of Distributed SAR

Synthetic Aperture Radar(SAR)is widely used in civil and military fields for its ability for all-weather and continual ground observation.However,it is impossible for conventional single-satellite single-channel SAR system to obtain the azimuth high-resolution and wide-swath at the same time because of the minimum antenna area constraint.Single-satellite Azimuth Multiple Phase Centers(AMPC)SAR and distributed SAR systems can break up the minimum antenna area constraint and realize high-resolution Wide Swath(HRWS)continuous imaging under the condition of low Pulse Repetition Frequency(PRF)for they increase spatial sampling by arranging multiple receiving channels along azimuth.Compared with single-satellite AMPC SAR,distributed SAR is more flexible,more diverse,safer and cheaper for its baselines along the azimuth and across the azimuth,but its complex baselines also bring difficulties to the signal reconstruction and imaging processing.This paper is aimed at the reconstruction of distributed linear array SAR signal and distributed three-dimensional array SAR signal.Methods for signal reconstruction under different baseline conditions were studied.And distributed SAR azimuth ambiguity suppression and imaging processing under different baseline conditions is realized.In the third chapter the situation of distributed linear array SAR is studied,and the signal model of distributed linear array SAR is established.The impacts to imaging,including distance envelope delay and the additional phase term,given by the expansion of the baseline length along the azimuth are discussed.The effects of these t wo items are analyzed by simulation and the signal processing flow of distributed linear array SAR while the ambiguity suppression method based on least squares are given.Finally,point target imaging was simulated for the distributed linear array SAR compared with the single satellite AMPC SAR.In the fourth chapter,the distributed three-dimensional array SAR is studied.The signal model of distributed three-dimensional array SAR is established.Partial approximation of the model was analyzed and the two-dimensional time domain and range Doppler domain model of distributed three-dimensional array SAR is derived.The frequency variation and the spatial variation of the phase term caused by the baseline cross the azimuth are analyzed.Under the condition where the baseline across the azimuth is not very large,this article supresses the azimuth ambiguity by aligning the envelope in time domain and reconstructing the steering vector in frequency domain.Finally the simulation is used to verify the effect of ambiguity suppression.