What is an Electronic Distance Measurement Device?
Electronic Distance Measurement (EDM) technology uses a ground-based, high-precision survey instrument (a theodolite) that emits a laser pulse to measure the time the laser beam travels from the theodolite to a mirror prism installed on the moving rock face. This is also called laser ranging. In theory, as the rock face moves downslope (toward the survey instrument), the distance between the survey instrument and the prism will decrease. Using this time, the distance can be precisely determined to one part per million (i.e., one millimetre over a distance of one kilometre).
