| Digital elevation model (DEM) store data array of point elevation information. It has a wide range of applications in civil, defense and military construction and the humanities and the natural sciences. In professional research of mapping, water conservancy andland using, DEM data is the basis of projects study. Synthetic aperture radar interferometry (InSAR) becomes a new remote sensing technology in recent two years, which belongs to microware RS technology divided by the use of RS band. InSAR technology makes use of microware interference principle. SAR sensor, carrying two antennas with one flight or one antenna with two flights, gets a pair of SAR images of the study area. Phase information of SAR data, from two reflected echo signal conjugate multiplication on the same ground object, converts into elevation with mathematical function relationship. In data processing, precise satellite orbit data and reference DEM are used as auxiliary data. At present, InSAR technology becomes one of the most potential methods to obtain mass DEM data over a wide range. This paper mainly analyzed the spaceborne radar data of ENVISAT-ASAR satellite and discussed key technologies in obtaining high-precision DEM in details.This paper aims at obtaining high quality DEM. Considering the integrity of the article, it introduced the basic theory of the spaceborne repeat track interferometry extracting digital elevation model, discussed the research status of processing key technologies of SAR data and focused on describing how to use six spaceborne images of ENVISAT-ASAR to obtain DEM of Anning city and its surrounding area. The main work of this paper is as follows:1. The working mode and principle of InSAR technology got further understood. Interference conditions formed by two images were summarized and the appropriate baseline length was deduced combined with theoretical formula.2. Based on discussing influence factors of interferometric phase quality, the impact of image registration on interferometric phase got analyzed in-depth.3. Interferogram filtering methods were discussed in details. Three filtering methods were used to interferogram de-noise processing with coherent coefficient as quality evaluation criteria of interferometric phase. Adaptability of different filtering methods was evaluated, based on experimental results.4. Several phase unwrapping algorithms were studied and phase ambiguity of filtered interferogram was processed with different phase unwrapping algorithms. According to phase unwrapping image pixels value statistics, characteristics of the different phase unwrapping algorithms were comparative analyzed.5. Theoretically formula derived the influence of some factors on InSAR system, such as position of the antenna, slant distance between antenna and ground point, phase difference, length of baseline and so on. At the same time, influence degrees of the baseline impact factors were further analyzed.6. On the basis of above studies, a detailed flowchart of processing SAR data of InSAR was given. According to this process, using six images of ENVISAT-ASAR data between 2009 and 2010, combining with SRTM DEM data, phase shifting into elevation of DEM was designed and implemented through complex image registration, eliminating flat effect, filtering of interference images, phase unwrapping, orbital refinement and geographic coding. Three groups results of DEM were got and DEM relative precision was assessed. |
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