Research On Bistatic SAR Echo Simulation For Undulating Terrain

SAR(Synthetic Aperture Radar)echo simulation refers to the computational simulation to obtain the raw echo data,which plays a pivotal role in the design,development of SAR systems and verification of imaging algorithms.Bistatic SAR echo simulation under undulating terrain conditions requires not only the consideration of the differences in simulation algorithms introduced by bistatic configurations,but also the analysis of the effects brought about by the undulating terrain,which is of great importance to promote the research and application of bistatic SAR.Focusing on the scattering coefficient calculation,shadow region determination and echo simulation algorithm involved in bistatic SAR echo simulation of undulating terrain,this thesis mainly carries on the following research work:(1)The bistatic SAR echo model is established,the echo law is analyzed,the point/face target echo simulation under ideal conditions is completed,and the mechanism of BP(back projection)imaging algorithm is studied,which lays the foundation for the subsequent bistatic SAR echo simulation of undulating terrain.(2)Aiming at the problem that the scene scattering coefficients in the traditional simulation method cannot reflect the influence of terrain undulation,a method for calculating the time-varying scattering coefficients of bistatic SAR in undulating terrain is proposed,which establishes the relationship between the instantaneous scattering coefficients and the incident angles of transmitting and receiving stations,and obtains the instantaneous scattering coefficients of bistatic SAR under undulating terrain conditions by combining the digital elevation data of the terrain.On this basis,the double-shadow phenomenon in bistatic SAR images is analyzed,and the relationship between the magnitude of azimuth and elevation angles of transmitting and receiving stations and double-shadow is revealed,which provides a guarantee for realizing accurate simulation of bistatic SAR echoes in undulating terrain.(3)Aiming at the problem of low accuracy of the traditional shadow judgment method,a shadow judgment method based on facet cell fitting and elevation angle comparison is proposed.Firstly,the terrain height on the same line of sight path with the target is obtained by facet cell fitting,and the corresponding elevation angle is calculated,and then the shadow judgment is made by using the elevation angle comparison method.This method effectively avoids the errors introduced by the plane wave assumption or multiple interpolation of the traditional method,and achieves the accurate judgment of SAR shadow of undulating terrain.(4)Aiming at the problem of low efficiency of traditional time-domain simulation algorithm,a bistatic SAR echo simulation algorithm based on equivalent scatterer and subaperture processing is studied and compared with the traditional range time-domain pulse coherence method and one-dimensional Fourier transform method.Based on this simulation algorithm,the bistatic SAR echo simulation under undulating terrain conditions is realized by combining the aforementioned bistatic SAR scattering coefficient calculation method and shadow judgment method,and the echo validation is completed based on the BP imaging algorithm.The above proposed methods are validated by simulation,and the results demonstrate that the bistatic SAR echo simulation in undulating terrain conditions can be effectively realized.