Research On Target Detection And Imaging Of Ground-based GNSS-R Bistatic Radar

Chinese land area is about 9.6 million square kilometers,which spans five time zones;the territorial sea area is 4.7 million square kilometers,and the eastern and southern mainland coastline is 18,000 kilometers;35 kilometers above the territorial sea and the territory are our national airspace.Due to the vast area of land,sea and airspace,the continuous development of the more sophisticated remote sensing technology is an important means to ensure the safety of national production and life.As important applications of remote sensing technology,target detection and imaging technology is widely used in military reconnaissance,vegetation monitoring,land planning and other fields.Traditional remote sensing satellites are limited by the high cost and long revisit period,and have deficiencies in coverage and real-time monitoring.The navigation satellites have a wide coverage and short revisit time.Therefore,the satellite-based bistatic radar system can continuously monitor the world for remote sensing.The bistatic radar system will greatly facilitate the observation of harsh regions such as the polar regions.This paper studies the detection and imaging of moving targets based on Beidou navigation signals.The main work and research results are as follows:Firstly,the bistatic radar signal model based on Beidou navigation signal is studied.The signal model equations including time delay,Doppler frequency,ionospheric error and receiver clock error are given.The synchronization scheme based on direct signal is studied.The theoretical time delay and Doppler frequency are obtained by calculating the orbit parameters of the satellite,and the synchronization error term is obtained by subtracting the actual tracking results.The compression process based on the direct signal is studied,and the bistatic distance is obtained by the strong correlation of the pseudo-random code in the Beidou navigation signal.Then the distance Doppler map is obtained based on the slow time domain Fourier transform,which contains the bistatic distance and Doppler frequency of the moving target to be tested.The distance Doppler map accumulating method based on motion compensation is also implemented.The energy accumulation on different distance elements increases the signal-to-noise ratio of the reflected signal.Based on the distance Doppler map,the quantitative advantage of the Beidou navigation satellite is studied to obtain the target position and velocity vector.The system scheme is given and verified by field experiments.Finally,the imaging method based on Beidou navigation satellite is studied.Firstly,the unique GEO satellite of Beidou system is used as the source of opportunistic illumination,which realizes the imaging method in multi-star single station and single-star multi-station mode,and has the advantage that the imaging result is not easy to defocus and the imaging algorithm has low complexity.The Beidou IGSO/MEO motion satellites are also used for imaging and utilize their synthetic aperture formed by motion during long accumulation time to obtain higher azimuth resolution.