Detection and Monitoring of Surface Subsidence Associated with Mining Activities in the Witbank Coalfields Using Differential Radar Interferometry

摘要

Surface subsidence associated with coal mining activities inthe Mpumalanga Province of South Africa changes the naturalenvironment in several ways, and current challenges for miningcompanies include rehabilitation of the natural environment andthe prevention of further degradation. To monitor the spatialand temporal evolution of surface subsidence, traditional fieldbasedmonitoring approaches such as GPS and spirit levelingare employed at a number of locations. However, the resultingmeasurements are point-based, and frequent revisitations arenecessary to map the evolution of surface subsidence basins overtime. To address these limitations, differential interferogramsderived from repeat-pass satellite-borne synthetic aperture radar(SAR) systems were tested for their ability to measure and monitorsurface deformation. The SAR data was captured by the EuropeanERS-1 and ERS-2 satellite and covered a timeframe between 2008-09-15 and 2008-09-15. The resulting interferograms revealedseveral features indicative of surface subsidence. Ground truthdata confirmed the presence of a subsidence basin, detected usingdifferential interferometry techniques during the 35-day periodbetween April 12, 2008 and May 17, 2008; a maximum verticaldeformation of 3.2 cm (1.3 in) was recorded. Interferometricmonitoring revealed an eastward migration of the subsidencebasin between June 2, 2008 and September 15, 2008 with anadditional 4.7 cm (1.9 in) of subsidence observed. This migrationcoincides with the advance of the working face of the mine duringthis period. Finite element modeling will be performed in orderto model the rates and evolution of surface subsidence haloes asunderground mining advances.These presented results demonstrate the ability ofinterferometric synthetic aperture radar techniques to measuresurface subsidence as well as the monitoring of the evolutionof subsidence basins over time. This implies that the techniquecould be included, together with traditional field-basedsurveying techniques, in an operational monitoring system.With knowledge on deformation rates and subsidence basinevolution, informed decisions on current and future infrastructuredevelopment can be made and remedial actions and preventionstrategies can be formulated for the problems associated withenvironmental degradation.