ABSTRACT
The contact between almost any material and a void space will create a high-amplitude reflection, which is readily visible in reflection profiles. As energy enters a void, it speeds back up to the speed of light, and there is no attenuation of the propagating waves until they hit the next surface that will reflect energy. As an aid in understanding what types of reflections might be generated from an arched void space with a flat floor, a two-dimensional model was produced using the software program called GPRSIM. The GPR method is almost the only geophysical technique that can find and map buried conduits for fiberoptic cables and other plastic pipes with no metal in them. All of the lava tubes tested was visible along ceiling collapse features, and their geometry could be mapped. Air waves, out-of-plane reflections, velocity pull-ups of the floor reflections, and a variety of reflections generated from edges and ceiling irregularities produce only confusing amplitude maps.
