Research On High-efficiency And High-precision Processing Techniques Of Spaceborne Interferometric Synthetic Aperture Radar

Spaceborne interferometric synthetic aperture radar can be all-time and all-weather to obtain high-precision digital elevation models and other value-added products over large areas, which has an extremely wide range of applications in military reconnaissance, national economic construction and scientific research. This paper, on the theme of studying data processing methods for spaceborne InSAR and on the purpose of providing algorithms for the design and implementation of ground data processing systems, made a systematic study on InSAR data processing issues. Based on the work of the formers, we studied image coregistration, phase filtering and unwrapping, DEM reconstruction and adjustment, SAR image ortho-rectification, product quality assessments and so on, and then proposed a number of high-efficiency and high-precision processing approaches of which significantly improved the processing performance. The major work and innovations in this paper are as follows:The issue of interferometric SAR image coregistration is studied in chapter 3. Here we analyzed the properties of various coregistration measure functions, made the real and complex correlation functions as the matching measures, designed the criterion for coregistration sensitivity, and achieved the adaptive selection of coregistration measure functions. Further, we proposed a coregistration method for interferometric SAR image by jointing the real and multiple correlation functions. Due to the combination of the respective advantages of the real and complex correlation functions, the new method has an improved accuracy and stability for coregistration compared to the traditional ones. In addition, as the correlation calculations can be achieved through the fast Fourier transformation, the new one still has a higher efficiency.The issues of interferometric phase filtering and unwrapping are sudied in chapter 4. By analyzing the statistical and signal properties of interferometric phase, we presented the concept of nonlinear phase model and the adaptive extraction method for nonlinear phase, and achieved high-precision approximation for the interferometric phase over a local window by using the nonlinear phase model of reflecting terrain contours. Then the application of nonlinear phase model in the interferometric phase filtering is studied. While the nonlinear phase compensation filtering is more fast and effective compared to other classic filtering methods in this paper. Finally, we do research on how to improve performance of phase unwrapping by using nonlinear phase model, and provide the concrete implementation steps of the improved branch cut method and region growing method. The real data processing results show that the improved methods can increase effectively the accuracy and speed of phase unwrapping.A fast and high-precision DEM reconstruction method is presented in chapter 5. Start from DEM reconstruction theory, we analyzed and revealed the two basic characteristics of the mapping relationship between the interferometric phase and the three-dimensional coordinate of target point. Based on this, we proposed a fast DEM reconstruction method, and provided the detailed steps of fast algorithm and the solutions of key parameters. The real data processing results show that the reconstruction speed is significantly improved only with a smaller accuracy loss, thus verifies the high efficiency and correctness of the method.DEM adjustment method is studied in chapter 6. From the input parameters obtained by simultaneously solving the three equations of DEM reconstruction, we summarized the error sources of affecting DEM reconstruction accuracy. By analyzing the characteristics and transferring regularity of various error sources, we concluded the main factors of affecting DEM reconstruction accuracy, and then provided DEM adjustment model. We divided the DEM adjustment into single-orbit data set adjustment and multi-orbit data set combined adjustment, and respectively studied the high-precision adjustment approaches in both cases. Due to the quality weighting matrix is introduced into the observational data, the parameter estimation of the adjustment model has a strong antinoise ability. The processing results from the simulation and real data show that the presented method can effectively improve the DEM accuracy.The ortho-rectification method of interferometric SAR image is studied in chapter 7. We discussed the geometric theory of spaceborne SAR geolocation and the error sources of affecting SAR geolocation accuracy, and analyzed the transfer relationship between the error sources and geolocation errors. According to the solution order of geolocation, we proposed the fast and high-precision forward ortho-rectification method and backward ortho-rectification method respectively. We analyzed the accuracy of the current typical four SAR satellites: Germany TerraSAR-X, Italy COSMO-SkyMed, Japan ALOS-PalSAR and Canada Radarsat-2, and the results show that the new method can fully satisfy application requirements for the precision. When the DEM data and SAR image for terrain corrected do not have a same source, we studied the method of eliminating the effect of ortho-rectification caused by relative system error between the two. The TerraSAR-X real data processing results show that the new method not only greatly improved computational efficiency but also maintained extremely high accuracy. The quality evaluation of interferometric SAR system products is studied in chapter 8. We discussed the characteristics of the evaluation indicators and the applicable of the algorithms for SAR image coregistration, interferometric phase filtering and unwrapping. We described the definition and formula for DEM accuracy specification, studied the quality evaluation methods of InSAR DEM products with different reference data, including point reference data, line reference data and surface reference data, and provided the detailed implementation steps of these methods. The high-precision DEM data from TanDEM-X is applied to DEM products of SRTM and ASTER for accuracy evaluation, and the experimental results obtained are in good agreement with the conclusions drawn by the published sources.