GeoModel - Ground Penetrating Radar (GPR)

How Ground Penetrating Radar Works

Ground penetrating radar (ground radar) operates by transmitting pulses of ultra high frequency radio waves (microwave electromagnetic energy) down into the ground through a transducer (also called an antenna). The GPR antenna (transducer) is pulled along the ground by hand or behind an ATV or a vehicle. The transmitted energy is reflected from various buried objects or distinct contacts between different earth materials. The antenna then receives the reflected waves and stores them in the digital control unit. The control unit registers the reflections against two-way travel time in nanoseconds and then amplifies the signals. The output signal voltage peaks are plotted on the GPR profile as different color bands by the digital control unit.

How Ground Penetrating Radar Locates Unmarked Graves at Cemeteries

GeoModel, Inc. conducts ground penetrating radar surveys for locating unmarked gravesites and confirming marked gravesites at cemeteries.

The GPR profile and cross-sectional diagram (below) shows several gravesites (caskets) detected using GPR. The soils at this site were very sandy and the caskets produced distinct anomalies. The GPR image shows that the condition of the graves are very distinct (more recent internments).

Using Ground Penetrating Radar to Locate Utilities and Pipelines

GeoModel, Inc. has been locating utilities and pipelines at sites nationwide using ground penetrating radar (GPR) since 1991. A utility or pipeline made of metal, PVC, or any other material that has different dielectric or conductive properties than the surrounding soils or rocks might be located with GPR.

GPR can locate gas, oil, and production pipelines, water lines, sewer lines, electrical duct banks, and large or bundled communication lines.

How Ground Penetrating Radar Antennas Work and Applications for Each Type

The depth to which ground penetrating radar waves can reach beneath the ground surface is mainly dependent on two conditions: 1) the type of soil or rock in the GPR survey area, and 2) the frequency of the antenna used. GPR can reach depths of up to 100 feet (30 meters) in low conductivity materials such as dry sand or granite. Moist clays, shale, and other high conductivity materials, may attenuate or absorb GPR signals, greatly decreasing the depth of penetration to 3 feet (1 meter) or less.

The depth of penetration is also determined by the ground penetrating radar antenna used. GPR antennas with low frequencies of from 100 to 200 MHz obtain subsurface reflections from deeper depths (about 25 to 100 feet or more in low conductivity soil and rock), but have low resolution. These low frequency antennas are used for investigating the geology and bedrock of a site, such as for locating sinkholes or fractures, to delineate deep landfills or trenches (with no clay cap), and to locate large, deeply buried objects.

GPR antennas with higher frequencies of from 300 to 1,500 MHz obtain reflections from shallow depths (0 to about 14 feet in low conductivity soil and rock), and have high resolution. These high frequency GPR antennas are used to investigate surface or shallow subsurface soils and to locate small or large, shallow, buried objects, such as utilities, pipelines, unmarked gravesites, archaeological sites, landfill trenches, underground storage tanks (USTs), buried drums, and also rebar in concrete.

Ground penetrating radar (GPR) data profiles are used for evaluating the location and depth of buried objects and to investigate the presence and continuity of natural subsurface conditions and features. Some of the Applications of ground penetrating radar (GPR) are given below.

• Utility Location Surveys
• Cemetery and Grave Surveys
• Sinkhole and Void Surveys