10.6.3 Photographic Image Analysis
Digital camera and computer technologies provide tools to derive far more information from images than was possible just a few years ago. Small differences between pairs of images can be readily detected, changes can be quantified in pixel counts or area percentages, and images are time stamped for easy sequencing and animation. These capabilities can be used to enhance mine slope monitoring. McVey and others (17) used a 35-mm camera and carefully positioned reflectors to measure deformation over time in an underground mine. Processed film has been used to measure deflections to a resolution of 0.5 mm, but the use of reflectors adds substantial complexity to the installation process and limits analysis to sites with reflectors. Photographic change detection can be used in a time lapse mode to record such things as bench loading, fracture development, creep and mass movements, and fallen rock sources. A real-time slope monitoring system using low-cost video cameras can be used to generate rock fall warnings where workers could be at risk.