Study On The Generation Of DEM Using Spaceborne InSAR

Digital elevation model(DEM) is a description of the terrain surface elevation information. It plays an important role in the civil engineering applications, the city landscaping and planning, the military construction, etc. Particularly, the 1:50000 high precision DEM data has a wide range of applications in the current situation of land use survey, thematic map production, update the smaller scale DEM data and other aspects. InSAR method has been widely applied in high precision DEM acquisition due to the advantages of wide monitoring range, high monitoring accuracy, all weather monitoring and other advantages.The research shows that Radar satellite includes the system errors of position and velocity, range distance measurement, baseline measurement and no fuzzy phase in the imaging observation of ground targets. These system errors will show as interferometric phase error and baseline error during the InSAR processing which affecting the accuracy of the final results.According to the interferometric phase error, The BEMD-Goldstein interferometric filtering algorithm was proposed in this paper. At First, the bidimensional empirical mode decomposition(BEMD) algorithm was used for interference graph decomposition; then, the local signal-to-noise ratio of the interferometric phase was estimated by decomposition results, which will be the new factor in the Goldstein filtering algorithm for the decomposition filtering. Finally, the filtering results were reconstructed for a new interferogram which was used for the last processing.Secondly, aiming at the problem of obtaining ground control point in mapping difficult areas, a new method of interferometric calibration based on reference DEM was proposed. Based on the slant range and Doppler model for reference DEM, realtionship was established between SAR and simulation SAR for obtaining the corresponding elevation information in SAR image. Then the elevation was used for the baseline calibration processing. In order to improve the accuracy of the sensitivity equation, the method of Newton descent was used to optimize the existing calibration models.Finally, the filtering algorithm was verified by simulated and measured images. The results show that the proposed algorithm can effectively maintain the interferometric edge details while suppressing the phase noise, and providing a better filtering interferometric for the acquisition of high precision DEM. At the same time, the TanDEM-X data of Yan Liang area in Shanxi province was used to verify the interferometric calibration algorithm, then the results were proved by some measured control points and the referenced DEM. The results show that the root mean square error of the check point was 1.95 m, and the root mean square error with the referenced DEM was 2.03 m, which meets the requirements of 1:50000 topographic mapping which proved the algorithm's reliability proposed. In addition, TanDEM-X images of Taiyuan in Shanxi Province and Shuanghu area in Tibet were also used. The experiments show that the proposed algorithm can provide high precision DEM results not only in mountains but also in high-mountain area and other complex terrain areas. The method has an important value for the engineering application of InSAR technology.