A Research Of High-precision Elevation Reconstruction Method On Multi-baseline Interferometric SAR

The multi-baseline interferometric SAR technology can break through the phase continuity constraints and achieve high-precision elevation extraction of the complex terrain,by fusing the information in the multiple interferograms.Based on the principle of elevation inversion,this paper mainly studies the phase unwrapping,elevation inversion formula and baseline estimation in the process of elevation inversion.The specific work and innovations made in this thesis are as follows:(1)Aiming at the problem that the unwrapping accuracy of the multi-baseline graph cut algorithm is not high when the number of baselines is limited,an improved multibaseline graph cut phase unwrapping algorithm is proposed.The phase of the slave interferogram is corrected in a way that the phase of the slave interferogram reference point is the baseline ratio of the phase of the master interferogram reference point.The modified phase of the slave interferogram is substituted into the maximum posterior probability phase estimation model to generate a noise-free multi-baseline likelihood function.Therefore,to reduce the influence of slave interferogram phase noise on the phase unwrapping of master interferometric phase.The simulation experiment proves that the algorithm performs well on steep terrain region and has great noise robustness.Besides,the method improves the accuracy of multi-baseline phase unwrapping when the number of baselines is limited.Compared with the multi-baseline phase unwrapping algorithm based on the two-stage planning method,which is not limited by the number of baselines,the improved multi-baseline graph cut phase unwrapping algorithm has the best phase unwrapping results under any coherence coefficient conditions.(2)Regarding the traditional altitude phase-based elevation inversion formula is imprecise,an accurate elevation inversion formula based on the absolute phase is established.Compared with the traditional formula,the use of the absolute phase for elevation inversion reduces the process of phase flattening.Also,the use of pixel slant distance matrix avoids the elevation error in the traditional formula introduced by using the reference point-slope distance instead of the global pixel point-slope distance.The altitude phase error has a greater impact on the accuracy of the traditional formula through error analysis.The accuracy of the phase unwrapping algorithm is required to be high to obtain high-precision elevation.In contrast,the absolute phase-based elevation inversion formula is only sensitive to the baseline inclination error,the platform height error and the target slope error.Therefore,when the parameter estimation is accurate,the absolute phase-based elevation inversion formula can significantly improve the elevation inversion accuracy.(3)Research on the baseline estimation method based on satellite orbit parameters,which estimates the space baseline by calculating the center point of the satellite orbit and calculating the baseline inclination according to the relative position of master and slave antennas.Construct a multi-baseline high-precision elevation inversion method,including interferometric phase preprocessing,improved multi-baseline graph cut phase unwrapping,baseline estimation based on satellite orbit parameters,and absolute phase-based elevation inversion,et.al.The effectiveness of each algorithm in this method is verified by using the measured spaceborne TerraSAR-X data.The experiment shows that high-precision inversion elevation(the accuracy is 1m)can be achieved after processing the interferometric phase by the improved multi-baseline graph cut phase unwrapping and the absolute phase-based elevation inversion formula,which meets the application requirements of spaceborne interferometric SAR elevation inversion.