Interferometric synthetic aperture radar and radargrammetry for accurate digital elevation model generation in New South Wales, Australia

摘要

A topographic map is a prerequisite to the thematic map of geological and environmental information. The Digital Elevation Model (DEM) has become an important source of topographical information for many scientific and engineering uses, such as hydrological and geological studies, infrastructure planning and environmental applications. Digital Elevation Models (DEMs) can be generated by using various techniques and by using a range of data sources, including ground surveying, photogrammetry, optical remote sensing, radar, and laser scanning.Where topographical data is unavailable, global coverage elevation data sets, typically DEMs based on remotely sensed data, can be the main source of information. Remote sensing techniques are a rapid means of acquiring elevation information over extensive terrain. In particular, processing remotely sensed data collected by Earth observation satellites is a very efficient and cost-effective mean of acquiring up-to-date and relatively accurate land cover and topographic information. Active remote sensing sensors (such as radar), which can operate in almost all weather conditions and also in darkness using their own illumination have become an important remote sensing technique.In radar remote sensing systems, DEM generation methods are based on the analysis of Synthetic Aperture Radar (SAR) images, and include interferometry, radargrammetry, radarclinometry, and polarimetry. The two most common methods for generating DEMs from SAR images are: (1) radargrammetry, a technique derived from photogrammetry and based on the stereoscopic principle, (2) interferometry, based on the phase differences between identical imaged points in two SAR images.This thesis describes the methods or techniques of DEM quality improvement and reduction in elevation errors, which are generated by various SAR techniques and imagery. InSAR DEM generation relies on the measurement of phase difference between two sets of complex radar signals, i.e. the range difference between the satellite-borne radar instrument and the ground targets reflecting the radar transmissions. In InSAR DEM generation, the so-called “master image” parameters, such as signal wavelength, incidence angle, and SAR image relationship (i.e. perpendicular baseline), affect the final DEM products. Furthermore, the different orbit direction (ascending and descending) provides a different representation of terrain and multi-temporal observation, leading to a more detailed representation of terrain over the same target area. Hence, ways of improving the quality of InSAR DEMs include using images collected by the satellite sensor from different orbit directions and multi-epoch data acquisitions. Also, in the case of InSAR DEM generation, major issues related to long satellite repeat-cycle times and low resolution DEM updating are discussed and solutions are proposed for ground distortion excluding method and selective elevation updating. Depending on the data acquisition conditions, the InSAR technique is less robust and more difficult to implement, particularly because the InSAR technique often produces poor results caused by poor coherence, atmospheric differences between two processed images and conditions. These three factors are influenced by the incidence angle and the Doppler similarity, which are quite stringent. InSAR requires the expectations of a certain baseline while interferometry is sensitive to the direction of sensor movements and some other factors. For this reason, the radargrammetry technique is an important alternative for DEM generation.