Research On Airborne SAR Radiation And Polarization Calibration Based On Point Target

As one of the main forms of SAR data acquisition,airborne SAR data acquisition has the characteristics of flexible data acquisition and has a wide range of applications in areas such as cloud mapping,geographic national conditions monitoring,and resource surveys.Fully polarized SAR can acquire backscattered signals of ground objects in different polarization states,and has important applications in the fields of surface parameter inversion and ground object classification.Radiation calibration and polarization calibration of polarized SAR data are the basis for quantitative application and research of polarized SAR data.The research on radiation calibration and polarization calibration of airborne SAR has important theoretical and practical significance.In this paper,based on the point target method,the radiation calibration and polarization calibration methods of airborne SAR are studied.The main research contents are as follows:(1)The key technology of high-resolution airborne SAR radiation calibration based on point target is studied.Based on the analysis of the main method and process of airborne SAR radiation calibration based on point targets,the key technologies such as the calculation of the response energy of the point targets,the fitting and correction of antenna patterns,and the calculation of the calibration constants are studied in this paper.The calculation of the response energy of the point target is to calculate the total response energy of the point target on the image,which is an important basis in the radiation calibration process.In this paper,the accuracy and adaptability of two point target response energy calculation methods for the high-resolution airborne SAR radiation calibration are analyzed experimentally.The results show that the integration method has higher relative radiation calibration accuracy and absolute radiation calibration accuracy.At the same time,its applicability conditions are more suitable for the research of airborne SAR radiation calibration.(2)A robust solution method of polarization calibration nonlinear model combining genetic algorithm and damped least squares is proposed.For the point target method,the accuracy of the theoretical model of airborne SAR polarization calibration and the classical polarization calibration algorithm Whitt algorithm and unconstrained calibration algorithm are relatively poor.Based on the theoretical model of polarization calibration,in view of the difficulty of the equation being ill-conditioned and requiring high initial values,this paper proposes a method of polarization calibration combining genetic algorithm and damped least squares.A high-precision robust solution of polarization distortion parameters from general matrix equations to complex nonlinear equations is achieved.This paper uses three polarization calibration methods to test the X-band airborne SAR data.In this paper,the qualitative and quantitative evaluation of the calibration results is performed using the polarization response map of the target before and after the calibration the PauliRGB images before and after the calibration,and the relevant quantitative parameters after the calibration The results show that this method has better calibration accuracy than the other two polarization calibration methods.At the same time,the method in this paper can solve the calibration parameters with at least two point targets,which reduces the dependence on the number of point targets compared with the other two methods.