Study on the Parameters-separated Solving Method of Airborne SAR Interferometric Calibration

Airborne interferometric synthetic aperture radar(In SAR) is one of the key methods to generate digital elevation model(DEM). As the accuracy of DEM would be affected by errors of In SAR system parameters, it is necessary to correct system parameters and compensate system errors using interferometric calibration. Most of the solving methods for airborne In SAR calibration establish the sensitivity matrix with antenna baseline length, baseline obliquity and phase bias jointly to calibrate parameters' errors, which can be referred as the parameters-coupled solving methods. Since the sensitivity of phase bias is much smaller than baseline length and baseline obliquity, it would easily cause the sensitivity matrix to be ill-conditioned when establishing the sensitivity matrix with the three parameters together. In this situation, errors of the solution vector could be amplified,which consequently affects the interferometric calibration accuracy, and increase the sensitivity of corner reflectors' locating heights to calculations. This paper presents a parameters-separated solving method for airborne InSAR calibration by separating the baseline length, baseline obliquity and phase bias during the calibrating-solving process. The method establishes the sensitivity matrix with baseline length and baseline obliquity firstly, to calibrate these two parameters. Then, the phase bias was fitted individually, and afterwards we acquire the integrated calibration result of all three parameters. According to the validation result of real SAR data obtained by the dual antenna airborne In SAR system, the condition number of sensitivity matrix established by the parameters- separated solving method drops from 1.07 E + 06 to 5.02 comparing with the parameters- coupled solving method. Also, the average deviation of height, which accounts for the differences between DEM that generated by the calibrated airborne In SAR system and the reference DEM with high accuracy, drops from 14.98 m to 6.51 m. The interferometric calibration accuracy is improved significantly. Furthermore, the result of simulation analysis demonstrates that the locating height of corner reflectors has no distinctive impact on interferometric calibration accuracy when using the parameters-separated solving method. Therefore, the parameters-separated solving method has a higher adaptability regarding to different locating heights of corner reflectors, which can effectively reduce the intensity of field works for airborne SAR interferometric calibration.