GPR creates pulses of radar energy at a surface antenna and projects them into the ground. As the transmitted radar waves encounter chemical or physical changes in the ground, energy is reflected back to the surface and recorded at the antenna. When the antennas are pulled across the surface in transects, a series of subsurface reflections are recorded. The GPR signal is plotted in a two-dimensional profile. When radar travel times are converted to depth, the GPR images can reveal some of the subsurface features and stratigraphic layers that are usually exposed during excavation. Three-dimensional GPR data are obtained by collecting many transects within a grid. When transects are spaced closely together and the reflections from all the transects are analyzed spatially, they produce a three-dimensional “cube” of the data.
GPR data is displayed in real time on the console so critical decisions can (in many cases) be made immediately. More detailed, quantitative analysis can be made in the office using the radar processing & interpretation software. GPR is a useful tool for underground mining, allowing mapping ahead of the face for depths up to 30m, mapping of hanging wall for depths up to 5m for safety reasons (rockfalls), location of boreholes, etc.