Research On Sub Aperture Imaging Technology Of Small Satellite SAR

Synthetic Aperture Radar(SAR)is an active microwave remote sensing technology for all day,all-weather and long-distance observation.It has abilities of certain penetrating ability,strong information acquisition and high-resolution imaging and has important practical value in military and civil fields.Small satellite SAR has the advantages of flexible launch,short development cycle,quick response and low cost.Therefore,it has obvious advantages in formation and network operation and become a research hotspot.High resolution wide swath(HRWS)imaging is an important development goal of SAR.With the continuous improvement of resolution and swath width,the radar echo data is bound to surge,which brings difficulties and challenges to small satellites with limited volume and weight in data storage and processing.Therefore,it is necessary to reduce the load of radar echo data while meeting the imaging requirements.In this dissertation,the sub aperture imaging algorithm of small satellite SAR is studied,and the imaging algorithm with low echo data is designed and simulated.The main researches of this dissertation are listed as follows:(1)Aiming at the spotlight mode of monostatic small satellite SAR,a real-time subaperture imaging algorithm based on RMA is proposed.By processing sub-aperture signal to reduce the Doppler bandwidth of the processed signal,the PRF only needs to be greater than the sub-aperture Doppler bandwidth to avoid azimuth ambiguity,which greatly reduces the amount of echo data to be collected by spaceborne SAR and solves the contradiction between high resolution and wide swath of monostatic SAR,so as to realize HRWS imaging.By dividing the whole aperture into several sub apertures,the radar can image the previously acquired sub aperture signal while acquiring the current echo signal,so as to realize real-time imaging.In order to achieve real-time imaging,the proposed algorithm uses modified RMA for range cell migration correction and range compression.Compared with the traditional RMA,the interpolation area of the modefied RMA is much smaller,which greatly reduces the calculation of Stolt interpolation and has more advantage in real-time imaging.(2)Aiming at the spotlight mode of distributed small satellite multiple-input multiple-output SAR(MIMO-SAR),a sub-aperture imaging algorithm is proposed to reduce storage pressure and imaging load in multi-channel high-resolution mode.The full-aperture signal of each channel is divided into sub-aperture signals.Then the subaperture signals are deblurred by using spatial filtering technology,and improved time domain bandwidth synthesis(TBS)algorithm is used to obtain large bandwidth signals.Then the sub-aperture images are obtained by using the sub-aperture image fusion imaging algorithm,and the sub-aperture images are fused coherently to obtain a highresolution image.Simulation results show that the improved TBS algorithm can synthesize bandwidth effectively,and the imaging effect of the proposed imaging algorithm is excellent,and the effectiveness and reliability of the proposed imaging algorithm are verified.