Identifying underground coal mine displacement through field and laboratory laser scanning

The ability to identify ground movements in the unique environment of an underground coalmine is explored through the use of laser scanning. Time-lapse scans were performed in an underground coal mine to detect rib surface change after different volumes of coal were removed from the mine ribs. Surface changes in the rib as small as 57 cm(3) were detected through analysis of surface differences between triangulated surfaces created from point clouds. Results suggest that the uneven geometry, coal reflectance, and small movements of objects and references in the scene due to ventilation air do not significantly influence monitoring ability. Timelapse scans were also performed on an artificial coal rib constructed to allow the researchers to control deformation and error precisely. A test of displacement measurement precision showed relative standard deviations of <0.1% are attainable with point cloud densities of >3200 pts/m(2). Changing the distance and angle of incidence of the artificial coal rib to the scanner had little impact on the accuracy of results beyond the expected reduction due to a smaller point density of the target area. The results collected in this study suggest that laser scanning can be a useful, comprehensive tool for measuring ground change in an underground coal mining environment. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)