The Integration of GPS, Satellite Radar Interferometry, and GIS Technologies for Ground Subsidence Monitoring

A variety of deformation surveying techniques have been extensively used for measuring the pattern of ground subsidence. These include precise levelling, total station traversing, aerial photogrammetry and GPS surveys. The impact on the surface infrastructure of underground coal mining to the southwest of Sydney is continuously monitored using a combination of these techniques. Since 2002, experiments have been conducted in the Appin area to test the feasibility of also using a remote sensing technique for ground subsidence monitoring. The technique uses the Synthetic Aperture Radar (SAR) images captured by several orbiting satellites, processed in a special way known as the differential interferometric SAR (DInSAR) to extract terrain change information. First, several ground features were surveyed as ground control points (GCPs) using Global Positioning System (GPS) receivers. Next, the GCPs were used in the radar interferometric processing of a pair of ERS-1/2 satellite images to generate a high-resolution digital elevation model (DEM) for the test site. In the third step, DInSAR processing was carried out using many combinations of repeat-pass satellite radar images. In this step the previosuly generated DEM was used to remove the topographic information so that any ground movement could be detected. In the last step, the DInSAR results were exported to a Geographic Information System (GIS) software package, and the mine subsidence regions examined. The subsidence can then be visualised in several ways, such as profiles, contour maps, and 3D views. Centimetre-accuracy results has been demonstrated for the Appin test site. Several results derived from data acquired by the Japanese JERS-1 and European ERS-1/2 satellites will be presented. Ground truthing and a comparison with subsidence modelling are currently underway, and the results of these validation studies will be reported on in the near future.