Measuring Cave Dimensions Remotely Using Laser Pointers And A Downhole Camera

An ongoing research program at Metzgar Fields, an athletic facility at Lafayette College in<br>Easton, Pennsylvania, has the primary objective of improving site investigation methods for karst<br>features using geophysical methods. Multi-electrode resistivity testing completed in 1999 located a<br>significant anomaly at the test site and subsequent borehole drilling confirmed that a two-meter high<br>void existed below approximately seven meters of bedrock. During the summer of 2003, we measured<br>the dimensions of this cave using laser pointers and a downhole camera originally designed for search<br>and rescue operations. The camera was lowered into the cave down one borehole and the laser pointers<br>were lowered down two other boreholes. Measurements were made using triangulation; the laser<br>pointers were adjusted so that they were aimed at the same point on the cave wall and measurements of<br>distances and angles were taken at the surface. The cave geometry we obtained will be used in the<br>future to make a quantitative comparison between the results of 2D and 3D resistivity testing and actual<br>cave geometry.