Study On Several Key Algorithms Of InSAR Technique And Its Application In Land Subsidence Monitoring

Land subsidence caused by coal mining, groundwater over-exploitation and so on, has become a serious problem for the development of society and economy. Therefore, many researchers are faced with a difficult task, which is how to monitor the land subsidence effectively and timely, analyze the formation mechanism and evolution law of subsidence, and provide technical support for the control of disaster. In this dissertation, a new advanced technique of earth observation, called InSAR (Interferometric Synthetic Aperture Radar), was studied in detail. Firstly, the basic principle and limitation of this technique was analyzed. Then, several improved key algorithms and experiments were studied. Finally, using the D-InSAR, PS-DInSAR and SBAS techniques, the subsidence of two experimental areas of Tianjin city and a coal mine, were obtained. The main research work and results in this dissertation are as follows:(1) The research statuses of InSAR technique were summarized. The insufficiency of InSAR and its related techniques studies were pointed out. The basic principles of SAR, InSAR and D-InSAR were described, and the application limitations of D-InSAR were analyzed.(2) A baseline estimation method based on the combination of precise orbits, the FFT (Fast Fourier Transform) and the ground control points was studied. A further research on the influence of estimation errors caused by the squint angle was analyzed. By comparing and analyzing the interferogram and sample altitudes, the correction and feasibility of the combination method are validated, and it can solve the problems of the single baseline estimation method to some extent.(3) An interferogram filtering method called considering the edge information based on DT-CWT was proposed, and its process flow was also designed. In the multiscale geometry transforming domain of DT-CWT, the edge coefficients were conformed by analyzing the transitivity of interscale coefficients and the correlation of intrascale coefficients. The edge and non-edge coefficients in DT-CWT domain were shrunk with different thresholds by the Bayes shrinkage function or the Bayes bivariate shrinkage function. The experimental results show that, this method restrains the interferogram noise stronger, and keeps the edges and details information of interferogram much better.(4) A new phase unwrapping method based on the hybrid particle swarm optimization algorithm (H-PSO) was proposed, and the least square phase unwrapping method was improved. By comparing with ten kinds of classical phase unwrapping methods, the correction of the methods studied in this dissertation is validated.(5) A relation model among confined water levels, exploitation quantity of groundwater, and the subsidence rate obtained by D-InSAR was established, and the experimental research on mining subsidence was also studied. In the experiment, the subsidence obtained by D-InSAR was smaller than the measured value. In order to solve this problem to some extent, two analysis methods for mining subsidence, such as the correction using control points and the multi-look process, were researched.(6) A method for selecting the master image called optimized coherence based on tangent function, and a double threshold algorithm based on the SNR of amplitude and phase for identifying PSC were proposed. Both of the two algorithms can be used as a supplement to existing methods.(7) The land subsidence of Tianjin city during 1992 and 1997 was obtained by PS-DInSAR and SBAS. 18906 and 42041 PS points were identified respectively by PS-DInSAR and SBAS. While, 16.4mm/a and 24.2mm/a of the maximal subsidence rate were obtained respectively by these two methods. Meanwhile, the subsidence during 1992 and 1997of a certain coal mine was calculated by SBAS method, and 380 PS points and 45mm/a of the maximal subsidence rate were obtained.