Radar satellite service checks stability of Africa's largest artificial hole   The Palabora mine's open cast pit measures almost 2000 metres across, making it the largest man-made hole in Africa. Owner Rio Tinto was concerned about subsidence in the vicinity, and called in AMEC, who applied a satellite radar technique called InSAR to the problem. Image courtesy of Rio Tinto.   Slant range deformation around the Palabora pit based on InSAR results, overlaid on a Quickbird high-resolution optical image. The area enclosed in blue exhbits fast motion, the area enclosed in green exhibits slow motion. Slant deformation provided by Vexcel; the Quickbird image provided by Infoterra Ltd, copyright Digital Globe Inc 2004, data courtesy of Eurimage.   Comparing slant range deformation around the Palabora pit for two months. The first image covers 22 July to 15 August 2004, the second image covers 15 August to 8 September. Note a decrease in deformation in the second image. For legend see the image above. The results are based on InSAR results, overlaid on a Quickbird high-resolution optical image. The area enclosed in blue exhbits fast motion, the area enclosed in green exhibits slow motion. Slant deformation provided by Vexcel; the Quickbird image provided by Infoterra Ltd, copyright Digital Globe Inc 2004, data courtesy of Eurimage.   At Kinross’s closed Hayden Hill gold mine in northeast California, AMEC studied InSAR data to help assess the stability of a waste rock dump that experienced five notable slope failures during the 1990s.   At Kinross’s closed Hayden Hill gold mine in northeast California, AMEC’s study of InSAR data focused on a waste rock dump that experienced five notable slope failures during the 1990s. AMEC prepared deformation maps for 24-day periods in the fall of 2001 and fall of 2002 and for an 11-month period stretching from the fall of 2001 to the fall of 2002. The maps show that the waste rock dump was relatively stable during those periods. However, since the availability of high-quality historical satellite data was limited to the fall of 2001 and 2002, new satellite data would be needed to investigate the current stability of the dump. Project team     The vicinity of the closed Hollinger gold mine near Timmins, Ontario has experienced extensive subsidence problems in recent years. AMEC found that Coherent Target Monitoring (CTM) based on radar satellite images could serve as a very useful prediction tool in owner Placer Dome’s subsidence-monitoring programme. AMEC’s study of satellite data between 1992 and 2003 found subsidence in the range of 25 millimeters to 55 millimeters in some areas where it previously was thought to be stable.   CTM-based subsidence measurements of Südsalz's working salt mine under the historic town of Bad Reichenhall. Nowadays freshwater is used to dissolve salt rocks into brine, which can then be pumped up via wells. The main high subsidence area is within the black rectangle. Südsalz is required by regulators to monitor subsidence at the site and has been doing so since 1988 using terrestrial leveling and Global Positioning System survey methods. Südsalz is interested in CTM and related InSAR technology as a possible means of reducing their monitoring costs. AMEC reviewed 10 years of historically available satellite data, generating 11,000 points of reference and found excellent agreement between the satellite data and the company’s survey findings. The CTM data was found to exhibit extensive coverage and redundancy over urban areas indicating spatially very smooth changes in deformation rates thus providing a high level of confidence in the data as well as insight into the types of deformation occurring. Release date: 5 January 2006