Study On Airborne DBF-TOPS SAR Imaging Method And Interference Experiment Verification

Synthetic Aperture Radar(SAR)is an all-weather,all-time,long-range and high-resolution imaging radar.Its many advantages make it irreplaceable in military and civilian fields.Interferometric SAR is the development of Synthetic Aperture Radar.It can achieve highprecision three-dimensional images while retaining the advantages of SAR.The representative working mode includes Terrain Observation by Progressive Scans SAR(TOPS SAR).The range multi-channel TOPS SAR system combined with Digital Beam Forming(DBF)technology,namely DBF-TOPS SAR,can effectively improve the signal-to-noise ratio of the image while ensuring the mapping bandwidth.This paper deeply analyzes the echo signal characteristics of the airborne TOPS SAR and DBF-TOPS SAR.In order to better understand the effect of the non-stationary motion of the airborne TOPS SAR and the inquality of channel characteristics of the DBF-TOPS SAR,we conduct three reasearches covering range from the motion error compensation to range DBF processing to channel error estimation and compensation.What's more,a TOPS In SAR Digital Elevation Model(DEM)generation experiment is conducted.The main work of this paper includes:1.To relieve the problem that the TOPS SAR normal offset angle varies spatially along the range and the variation does not meet the linear approximation condition,an improved DBF processing method based on range-based blocking is proposed.Based on the analysis of the characteristics of the single-channel TOPS SAR mode,the range multi-channel TOPS SAR echo signal model and the range DBF principle are studied,and three existing methods of distance DBF processing are compared and analyzed.For the characteristics of spatial variation along range of the normal offset angle,through block processing along range,the normal offset angle in the block and the range sampling time approximately meet the linear characteristics.Taking a single range block as an example,the DBF processing process is derived in detail,and the simulation data processed results verify the effectiveness of the method in this paper.2.As for the airborne TOPS SAR platform motion error and beam pointing spatial variation,an azimuth spatial variation error motion compensation method for motion error projection along the line of sight is proposed.The motion error model of airborne TOPS SAR in nonideal motion is established.When performing vertical route motion compensation,combined with the characteristics of TOPS SAR azimuth beam pointing change,calculate the motion error by projecting along the sight to the ideal track.The theoretical analysis and simulation results verify the accuracy of the motion error model in this paper,and further verify the effectiveness of the motion error compensation method proposed in this paper by using airborne measured data.3.About the problem of inconsistent channel characteristics of airborne DBF-TOPS SAR,a channel error estimation and compensation method based on coherent coefficient weighted filtering is proposed.The range multi-channel echo signal model with channel error is analyzed.And we determiane the filter weight coefficient according to the coherent coefficient,which effectively improves the calculation efficiency of the filter weight coefficient.Simulation and measured data processing verify the method effectiveness.4.Based on the principle of In SAR processing,the results of each step of TOPS In SAR are given.For the first time,the generation of airborne TOPS In SAR digital elevation maps has been achieved in China,which verifies the feasibility of high resolution wide-swath mapping of airborne TOPS In SAR.