Detection and monitoring of surface subsidence associated with mining activities in the Witbank Coalfields, South Africa, using differential radar interferometry

Subsidence associated with coal mining activities in South Africa changes the natural environment in several ways. To monitor the evolution of surface subsidence, traditional field-based monitoring approaches, are employed. These measurements are point-based and frequent visits are necessary to map the evolution of surface subsidence basins over time. To address these limitations, differential interferograms derived from satellite-borne synthetic aperture radar (SAR) systems were tested for its ability to measure and monitor surface deformation. The SAR data was captured by the ERS-1 and ERS-2 satellites and covered a time frame between 2008-09 15 and 2008-09-15. Field data confirmed the presence of a subsidence basin detected using differential interferometry techniques during the 35 day period between 2008-04-12 and 2008-05-17 with a maximum vertical deformation of 3.2 cm being recorded. Interferometric monitoring revealed an eastward migration of the subsidence basin between 2008-06-02 and 2008-09-15 with an additional 4.7 cm of subsidence being observed.