Research On Key Techoniques Of Bistatic SAR

Bistatic synthetic aperture radar(BiSAR),which using spaceborne radar as illuminator of opportunity and the receiver is mounted on the airborne platform or fixed on the ground,is a kind of novel radar system.It can work all day in all weather conditions and can acquire high-resolution microwave images,so it has recently been an interesting research hotspot.In practice,the BiSAR system is well characterized by placing the transmitter and the receiver on separate platforms.Using appropriate bistatic configurations,several additional benefits can be obtained,such as improving the performance of target feature extraction and classification,and increasing the survival ability of the SAR system in conflict areas.In this paper,two different BiSAR systems are introduced and analyzed: the spaceborne-ground BiSAR system and the spaceborne-airborne BiSAR system.This dissertation focuses on the system characteristic,raw data simulation,beam footprint detection and tracking and imaging algorithms for the two particular BiSAR systems.Through the in-depth study of the mentioned techniques,some valuable research results are achieved.The main works and achievements of this dissertation are summarized as follow:1?The geometric configurations and characteristics of above two BiSAR systems are studied.Problems common to the two systems such as beam footprint relative motion and synchronization technique are also studied.The main work includes:(1)The system concepts of the two systems are presented,and then the system characteristics,such as signal-to-noise ratios(SNR)of the direct-path signal and the reflected signal,range and azimuth resolutions,are deeply analyzed.(2)Based on the ratio of the beam width to the velocity,a scheme for the computation of integration time and azimuth coverage of BiSAR is presented.(3)The performance of the synchronization technique which based on the direct-path signal is analyzed.2?The raw data simulation method for the BiSAR system is studied.The main work includes:(1)With the combination of 2-D inverse Stolt transform in the 2-D frequency domain and phase compensation in the range-Doppler frequency domain,a rapid raw data simulation method for fixed-receiver BiSAR system is proposed.(2)Based on the two-dimensional(2-D)frequency spectrum of fixed-receiver BiSAR with time and frequency synchronization errors,a rapid raw data simulation method is proposed in this paper.(3)A high precision time-domain raw data simulation method for double sliding spotlight BiSAR system is proposed.3?The beam footprint detection and tracking method for non-cooperative BiSAR is studied.The main work includes:(1)The reflected signal model of the scene is derived and the performance of the conventional detection methods is analyzed.(2)Based on the cross-correlation and Constant False Alarm Rate(CFAR)detection,a beam footprint detection and tracking method is proposed.(3)The vehicle-based BiSAR experiment is introduced and the proposed beam footprint detection is validated by the experimental data.(4)Based on the relationship between the Doppler spectrum parameters and the beam footprint center distance of the raw signal,a beam footprint tracking method is proposed.Simulation results are presented to validate the feasibility and efficiency of the proposed method.(5)The airborne BiSAR experiment is introduced and the proposed beam footprint tracking method is validated by the measured data.4?The imaging algorithms for multi-mode BiSAR system are studied.The main work includes:(1)The characteristics of the raw signal after synchronization by the direct-path signal are analyzed.(2)By combining azimuth preprocessing,direct-path signal compensation and nonlinear Chirp Scaling(NLCS)imaging algorithm,a new focusing algorithm for sliding spotlight BiSAR with a fixed-receiver is presented.Results of point targets simulation and measured data are presented to validate the efficiency and feasibility of the proposed imaging algorithm.(3)The system characteristics of the double sliding spotlight BiSAR system are analyzed.Based on the Method of Series Reversion(MSR),a new focusing algorithm is presented.Simulations are performed to validate the efficiency and feasibility of the proposed imaging algorithm.The validation and performance of the proposed methods in this dissertation are examined by abundance of simulated and experimental data.The results show that the proposed methods are proved to be of good application values.