Optical projection and image processing approach for mine wall monitoring

Wall movement in an underground mine must be continually monitored to provide real-time assessment of dynamic stress changes around mining excavation and to warn against rock failure. An in situ approach using optical spot projection and image processing can measure submillimeter movements. The system can be easily automated and poses no obstruction to mine traffic. The position of an off-normal laser spot will shift as the target wall moves. The centroid of this projected spot can be measured through image processing of a digital image. Multiple laser spots give the system simultaneous information over a larger sampled area. Software processing can measure subpixel shifts of the spot centroid. The resolution depends on the pixel count, the magnification of the camera lens (and hence the field of view), the optical-beam angle, and the spot characteristics. A laboratory table-top experiment demonstrated the system for distances up to 3 m and for a resolution of 0.1 mm. The results were linear in target movement, with standard errors between 0.83% and 5.38%. An automated system is described for a mine environment. (c) 2007 Society of Photo-Optical Instrumentation Engineers.