Mine subsidence is the settlement of a part of the earth’s crust due to removal of subsurface solids or underground excavation. This settlement may vary in magnitude, ranging from complete collapse, substantial lowering or small distortions of the ground surface. Several types of sub-surface mining or resource extraction will result in subsidence. Mining-induced subsidence is almost always localised to the surface above the mined area, plus a surrounding buffer area. The vertical magnitude of subsidence can cause damage to the natural environment, buildings and infrastructure. This subsidence can be successfully managed through careful planning, accurate measurements, regular monitoring, preventive measures and carrying out necessary repairs.
The area we will examine in this case study contains a coal mine and coal bed methane (CBM) well pads. Subsidence is usually associated with both coal mining and natural gas extraction, therefore subsidence is expected in the area. SAR data from the Sentinel-1 satellites and Differential Interferometic SAR (DInSAR) processing techniques are used to measure the level of subsidence over this area. Data between two time periods are used to evaluate the rate of subsidence over time.
An interferogram indicating phase difference between two data acqusitions over the area of study is seen below. Several areas of high coherence are seen in the image below, over buildings at the lower periphery of the mining site and over some of the well pads. Noise (coherence loss) in the rest of the image is due to the large changes between the periods of data acquisition (vegetation movement/growth, excavation/construction etc.)
The ground displacement raster seen below (over satellite base-map) represents only coherent pixels, ground subsidence from 6 cm / year to 12 cm / year can be seen in the image below. Higher subsidence rates are seen over the gas extraction well pads, than around the mining site. Although a large amount of information is lost due to low coherence, the analysis gives a good indication of ground subsidence in the area in the proximity of the mine and well pads.
Satsense.co 