Ground-Penetrating Radar

In principle, Ground-penetrating Radar (GPR) is a very simple geophysical technique. An antenna transmits a pulse of electromagnetic energy into the ground and when that energy encounters a material with different electrochemical properties, part of the radar pulse bounces back toward the surface--where the antenna detects it upon return. In reality, this geophysical technique is one of the most complicated, both in terms of instrument technology and data processing. However, the complications are well worth the effort because of the incredible utility of GPR.

Examples of Radar Surveys   Historic Foundations and Cellars Wells and Other Historic Shaft-Type Features Graves and Cemeteries Buried Paths, Roads, and Utilities Prehistoric Features Urban Lots Industrial sites

The Sensors and Software Noggin Radar System, with a 500 MHz antenna. Survey in DeRivera Park, Put-in-Bay, South Bass Island, Ohio, Lake Erie. Searching for War of 1812 graves.

How Ground-Penetrating Radar Works

In essence, GPR surveys generate cubes of data. The top of the cube is the ground surface and the bottom is the maximum depth at which reflections can return to the surface and be detected. The sides of the cube are the horizontal limits of the survey area. Perhaps the most unique and useful aspect of GPR surveys is that the cube of data can be cut into horizontal slices, each of which represents a horizontal plan map of the survey area at different depths (depth is estimated from radar velocity). The image below is a time slice map of a 20x30 meter area in a park in Worthington, Ohio. Numerous utility trenches, and the pipes within them, were detected below ground. Note how the actual pipes do not show up in the time slices until at least 50 cm below surface, though in some cases the trenches are visible at shallower depths.