Methodology Of DEM Generation With SAR Imagery And Its Accuracy Analysis

As a microwave sensor, synthetic aperture radar (SAR) is capable of acquiring images day and night as well as through cloud and rain. It is well known that either aerial or satellite photogrammetry is affected by adverse weather condition when applied to topographic mapping. For example, the southwestern part of China is frequently covered by heavy cloud, and thus resulting in failure with photogrammetry. In order to complement the limitation of photogrammetry, many investigators have recently been interested in the theory and method of three-dimensional (3D) reconstruction with SAR imagery. This leads to the birth of two techniques, i.e., interferometric synthetic aperture radar (InSAR) and radargrammetry, which have exhibited great potential in the field of topographic mapping.In view of the unique features and merits of imaging SAR, this thesis describes the characteristics of SAR image and the fundamentals of InSAR and radargrammetry. The in-depth studies have been performed on generating digital elevation model (DEM) with the combined use of the two techniques. The main research contents are outlined below.(1) The multiple SAR images acquired by ERS-1/2 over Hong Kong are used to form several interferometric pairs for DEM creation. The reference DEM produced from digital topographic maps with scale of .1:20000 is utilized to evaluate the accuracy in interferometric DEM. The testing results show that 10-m accuracy in elevation can be obtained with InSAR. The main limiting factors are temporal decorrelation and atmospheric contamination.(2) The multiple SAR images acquired by ERS-1/2 over Hong Kong are used to form stereo pairs for DEM creation by radargrammetry. In comparison with the reference DEM, the DEM created in this way is assessed in terms of accuracy. The impact factors are also analyzed, including terrain parameters such as slope and aspect, as well as time intervals of stereo pairs. The testing results show that 30-m accuracy in elevation can be obtained with radargrammetry. Both temporal and atmospheric factors almost have no influence on DEM accuracy. However, both terrain slope and aspect have significant impacts on DEM accuracy. The larger the slope, the worse the accuracy in elevation; if the slope is greater than 30°, the elevation error would be unacceptable. Moreover, the DEM accuracy relies on terrain aspect.(3) Taking into account the factors limiting DEM accuracy, a fusion method with the combined use of two types of DEMs is proposed to improve DEM accuracy. Such fusion method is based on a weighted average of the two types of DEMs by using correlation coefficients as weights.(4) The SAR orthoimage over Hong Kong is finally generated with the use of the fused DEM.This study aims to systematically understand the characteristics of SAR image, the theory and method of 3D reconstruction with SAR imagery, and to explore how to improve accuracy in radar DEM. This study is significant for map generation and land survey in west part of China.