Assessment of the progression of coal mine subsidence in Colorado, using InSAR

Abstract

Coal mine subsidence is the deformation of the Earth’s surface caused by the collapse of rock and unconsolidated deposits into underground mine voids or entries, induced by the extraction of coal. This deformation can cause damage to roads, buildings, utility lines, or pipelines. Colorado’s history of coal mining dates back to the beginning of the 20th century and continues to this date. Inactive mines in Colorado pose a potential risk for 25,000 people along the front range urban corridor. An important step towards mitigating this problem, is to assess the applicability of remote sensing techniques for characterizing the vertical displacement, lateral extent, and formation sequence of subsidence features, in relation to the extent and timing of mining activities. This project evaluates the applicability of Interferometric Synthetic Aperture Radar (InSAR) for quantifying and delineating the progression of subsidence from active coal mines in Colorado. The data used for this analysis is limited to SAR images collected by the Advanced Land Observation Satellite (ALOS), the Environmental Satellite (ENVISAT) and the European Remote Sensing (ERS) satellites I and II. Three study areas were selected to assess the method’s applicability under different conditions (density of vegetation, topography, activity status, and mining method). The study areas are the Deserado Mine, the King Coal II Mine, and the historical mining complex in Colorado Springs. The pertaining imagery was archived in a database, organized by the relative orbit and frame of provenance. SAR images were processed with General Mapping Tools SAR (GMT5SAR) and the Generic InSAR Analysis Toolbox (GIAnT) to produce a time series of quantified deformation. The results were ultimately compared with the extent of mine workings and subsidence models to assess the accuracy of the results. Clear subsidence signatures were found over the Deserado Mine and the King Coal II mine. Deformation above the longwall mine (Deserado) was detected with all the utilized data sets, proving that InSAR can be used to delineate the extent of subsidence over such type of mines. Deformation above the active room and pillar mine (King Coal II) was only detected using ALOS data. No clear signs of deformation were found within the historical mining complex in Colorado Springs. The low density of coherent pixels limits the use of InSAR for delineating troughs above such mine type.