DEM Generation In Mountainous Area With Differential InSAR Technique

Digital elevation model (DEM) is very vital spatial geographic information, which plays an important role in related research and national economy fields, such as resource exploration, disaster prevention and mitigation, infrastructure planning and construction and so on. However, in Western China, due to complicated topography, high altitude, thin air and some area are even affected by mist wheather throughout the year, conventional methods of elevation data acquisition are difficult to apply. Interferometric Synthetic Aperture Radar thechnology can help obtain large extent, fast and high precision elevation data. It makes use of two or more correlated SLCs in the test area to extract its height information with an accuracy high to meters. In this thesis, the problems existing in the DEM reconstruction based on InSAR technique are discussed, which put forward the application and development in terrain mapping field.The study is around the theory and technical flow of the DEM construction algorithm based on InSAR technique. Aiming at the key processes of SAR data processing, i.e., baseline estimation and phase unwrapping, a new baseline estimation method and an elevation information extraction algorithm by D-InSAR technique applicable in mountainous area are broughtforward to attain more accurate elevation data in relief area. The main research work in the thesis are as follows:Firstly, analyse the error sources of the height acquired by InSAR techniqueBased on the geometric and mathematical model of elevation extraction by InSAR, we explore the error sources that affect the height accuracy, and theoretically analyse the sensitivities of the main error sources to height estimation.Secondly, present a baseline estimation method immune to topography condition.After making an analysis of the characteristics and the applied condition of the existing InSAR baseline estimation algorithms, we propose a new baseline estimation algorithm less relying on terrain relief-InSAR baseline estimation algorithm based on coregi strati on offsets. Experiments with the real data acquired in Tibet by Envisate satellite are conducted to validate the algorithm.Thirdly, a DEM construction algorithm by differential InSAR technique based on phase compensation is proposed.Aiming at the problem of phase unwrapping diffculty in large baseline interferograms, we firstly make a simple analysis of the characteristics and defiency of the conventional DEM construction algorithm by InSAR and D-InSAR. Then, a DEM construction method by D-InSAR technique based on phase compensation is proposed. Experiments with the ERS-Tandem data acquired in Kunlun Mountain verify the feasibility and efficiency of the algorithm.Fourthly, discuss the relationship between the elevation accuracy and the topography condition and the coherenceTaking the DEM obtained by the algorithm proposed in the paper as an example, we use statistical method to analyse the height accuracy under different topography and coherence conditions. The experiment results demonstrate that the accuracy of the obtained DEM is positively correlated to the coherence and the topographic slope, and that of the slopes bending away from the SAR look direction is more accurate than those facing the radar antenna. Therefore, if the slope of test area is less than 45 degrees, SAR images with greater incidence angle will be advantageous for high-precision DEM generation.