Study Of Geosynchronous Orbit SAR 3-D Imaging Technology

Spaceborne Synthetic Aperture Radar(SAR)is a radar system that uses satellites as the carrier to observe the ground.It has the advantages of wide swaths,freedom from borders,meteorological conditions,etc.It has great potential for development in practical applications.At present,orbiting satellite-borne SAR imaging satellites are all low-altitude satellites.The altitude of the orbit does not exceed 1,000 km,and the revisit period for the same area is generally 3 to 4 days.However,the difficulty coefficient of satellite-borne SAR observation missions has been continuously improved,such as geological disaster monitoring,oceanic characteristics analysis,etc.These applications require spaceborne SAR to frequently observe large-area target scenes,and impose more stringent requirements on satellite systems for spaceborne SAR.In order to overcome the shortcomings of long-term re-visiting of low-orbit SAR satellites and small coverage area,an effective approach is to increase the orbital altitude of satellites to a geosynchronous orbit(higher orbit)above 30,000 km.This high-rail platform can effectively expand the scope of the observation area,and a single beam can cover a width of several hundred kilometers to obtain a large-scale,continuous observation of the earth.At present,the research on GEO SAR mainly focuses on the two-dimensional imaging algorithms.However,in many practical applications,such as geological disaster detection,marine application research,and target recognition,there is a demand for three-dimensional imaging of GEO SAR.It is required that the GEO SAR not only has a high temporal resolution but also has a certain spatial resolution.In this paper,the three-dimensional tomography imaging technology is applied to the GEO SAR system to realize the three-dimensional reconstruction of the target by the GEO SAR.The main research work of the thesis is as follows:1.Establish a multi-baseline GEO SAR 3D imaging model,use a multi-satellite approach to form a synthetic aperture at altitude,then three-dimensional imaging of GEO SAR is achieved by pulse compression.2.Due to the influence of its own control system and space gravity and other factors,the trajectory distribution of the GEO SAR system is inhomogeneous,and directly adopting the Fourier transform will seriously affect the imaging resolution of the high dimensionality.Based on this,a three-dimensional imaging algorithm of GEO SAR based on NUFFT is proposed.The simulation of the point target shows that the algorithm has a good imaging effect under the highly non-uniform sampling model,and further gives the window function for the high dimensional imaging results.The influence of the window function on the high-dimensional imaging results is further given,which provides the choice of window function.3.In practical applications,the trajectory baseline of the GEO SAR three-dimensional imaging system is sparse,and the baseline interval is relatively large.It is difficult to achieve high-precision three-dimensional imaging based on Fourier transform and NUFFT.Aiming at this problem,a three-dimensional reconstruction algorithm of GEO SAR based on sparse representation is proposed.The high dimensional imaging is modeled as a sparse reconstruction problem,which reduces the trajectory requirements of the multi-baseline GEO SAR three-dimensional imaging system and improves the algorithm's applicability,point target simulation verified the correctness and effectiveness of the proposed algorithm.