Airborne Bistatic Forward-looking SAR Motion Error Estimation And Compensation Based On Raw Data

Airborne bistatic synthetic aperture radar(SAR)technology could achieve twodimensional high-resolution imaging in the forward-looking area of the receiving platform,which has important application value in the fields of reconnaissance,surveillance,navigation,guidance,etc.,and is a research hotspot of radar imaging.However,due to the influence of spatial-separated geometry and forward-looking receiving beam,motion error of airborne bistatic forward-looking SAR(BFSAR)has properties of high degrees of freedom and strong spatial variation,which causes twodimensional defocusing and centrifugal distortion in SAR images,and severely affects the imaging quality.Constrained by the measurement accuracy,cost and other factors,motion error of airborne BFSAR cannot be fully compensated by estimation and compensation methods based on motion measurement data.As a result,motion error estimation and compensation methods based on raw data are required.In this dissertation,theoretical research,numerical simulation and experimental validation are carried out on the echo model,error characteristics,error estimation and compensation methods involved in airborne BFSAR motion error estimation and compensation based on raw data.The main contents of this dissertation are as follows:1.Motion error models of airborne BFSAR are established,and the analytical relationship between the three-dimensional trajectory error of the platforms and the Doppler frequency error of echo is derived.High-order characteristics of range cell migration(RCM)error and strong two-dimensional spatial-variant characteristics of Doppler phase error of airborne BFSAR are analyzed.The theoretical basis for studying airborne BFSAR motion error estimation and compensation methods based on raw data is provided by the models and analysis above.2.An RCM and Doppler phase error pre-compensation method under the condition of time/frequency error and motion error coupling is presented.By utilizing the difference between the spatial-variant characteristics of motion error and the spatial-invariant characteristics of time/frequency error,effective separation of the time/frequency error and the motion error could be achieved,and problem that the time/frequency error interferes with the motion error estimation and compensation process could be solved.A satisfactory prerequisite for conducting raw-data-based airborne BFSAR motion error estimation and compensation process could be provided by utilizing this method.3.An RCM error correction method based on error amplification feature inversion and an RCM error correction method based on instantaneous Doppler mapping are proposed,which could solve the RCM error amplification and trajectory spreading problems in azimuth-frequency domain RCM correction process and cross-cell RCM error problem in azimuth-time domain RCM correction process,respectively.RCM error caused by airborne BFSAR motion error could be corrected by utilizing these methods.4.A two-dimensional spatial-variant Doppler phase error compensation method based on airborne BFSAR motion trajectory error estimation is proposed.In this method,Doppler error of airborne BFSAR echo is estimated firstly.Then the three-dimensional error of airborne BFSAR trajectories is estimated.Finally,the two-dimensional spatialvariant Doppler phase error could be compensated by using the estimated error trajectories,and the problem of centrifugal distortion in SAR images caused by airborne BFSAR motion error could be solved.Methods proposed in this dissertation are verified by numerical simulations and experimental data.Results show that the proposed methods could achieve decent estimation and compensation for the high-order RCM error and two-dimensional spatialvariant Doppler phase error caused by airborne BFSAR motion error,and the quality of airborne BFSAR images could be improved.