Rebar located with ground radar (GPR) by GeoModel, Inc.ground penetrating radar, ground radar, gpr, or underground scanning of buried tanks surveyed by GeoModel, Inc.GeoModel, Inc. Logo

 

 

 

Basic Operating Principles of Ground Penetrating Radar

Email us at geomodel@geomodel.com or phone 703-777-9788

 


What is Ground Penetrating Radar?

Ground penetrating radar (GPR) is a nondestructive geophysical method that produces a continuous cross-sectional profile or record of subsurface features, without drilling, probing, or digging. The GPR cross-section shows the ground surface at the top of the profile, and the reflections of subsurface geologic units and objects to a certain depth at the bottom.

GeoModel, Inc. GPR profile obtained at a cemetery site

 

Ground penetrating radar (GPR) 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, as seen in the two examples below.

Three buried tanks located by GeoModel, Inc. using GPRGeoModel, Inc. karst bedrock topography using GPR

Three Buried Tanks (on left) and Irregular Karst Bedrock Topography (on right)

 


Ground Penetrating Radar Basic Operating Principles

Ground penetrating 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).

GeoModel, Inc. 400-MHz antennaGeoModel, Inc. 200-MHz antenna

GeoModel, Inc. 400-MHz Antenna (on left) and 200-MHz Antenna (on right)
(Manufactured by GSSI - Geophysical Survey Systems, Inc.)

 

The ground penetrating radar antenna (transducer) is pulled along the ground by hand or behind a vehicle.

Hand-towed GPRVehicle-towed GPR

Hand-towed 400-MHz antenna GPR Survey and Vehicle-towed 200-MHz antenna GPR survey

 

The transmitted energy is reflected from various buried objects or distinct contacts between different earth materials.

GPR signal transmission, geomodel.com

Diagram showing how the GPR signal reflects from a Buried Pipe and returns to the GPR antenna

 

The antenna then receives the reflected waves and stores them in the digital control unit.

GeoModel, Inc.'s SIR-2 GPR Digital Control UnitGeoModel, Inc.'s SIR-3000 GPR Digital Control Unit

GeoModel, Inc.'s SIR-2 GPR Digital Control Unit and Newer SIR-3000 GPR Digital Control Unit
(Manufactured by GSSI - Geophysical Survey Systems, Inc.)

 

The GPR antenna needs to have good contact with the ground surface in order for the GPR antenna to register the ground surface. When the GPR antenna signal does this, it creates an "air wave" as shown in the GPR image below.

When the transmitted signal enters the ground, it contacts objects or subsurface strata with different electrical conductivities and dielectric constants. Part of the ground penetrating radar waves reflect off of the object or interface; while the rest of the waves pass through to the next interface. On the right side of the bedrock GPR image below, the sloping bedrock layer can be seen above a horizontal bedrock layer.

Principles of GPR - Cross-Sectional Profile

 

The reflected signals return to the antenna, pass through the antenna, and are received by 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 ground penetrating radar profile as different color bands by the digital control unit.

For each reflected wave, the radar signal changes polarity twice. These polarity changes produce three bands on the radar profile for each interface contacted by the radar wave.

The depth scale for the GPR profile is calculated from the two-way travel time in nanoseconds and the dielectric constant (DI) of the subsurface soils or rocks.

 


How Deep Can Ground Penetrating Radar Go Into the Ground?

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.

Ground penetrating radar 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 GPR antenna used. Antennas with low frequencies of from 25 to 200 MHz obtain subsurface reflections from deeper depths (about 25 to 100 feet or more), but have low resolution. These low frequency antennas are used for investigating the geology of a site, such as for locating sinkholes or fractures, and to locate large, deeply buried objects.

Classic sinkhole discovered by GeoModel, Inc. using GPRDeep Burial Trenches located by GeoModel, Inc. with deep GPR

 

Antennas with higher frequencies of from 300 to 1,500 MHz obtain reflections from shallow depths (0 to about 18 feet), and have high resolution. These high frequency antennas are used to investigate surface soils and to locate small or large, shallow, buried objects, such as utilities, gravesites, and also rebar in concrete.

Multiple underground pipes detected by GeoModel, Inc. using ground penetrating radar Gravesites located by GeoModel, Inc. with GPRGeoModel, Inc. ground penetrating radar image of rebar and pipe conduit in concrete

 


 

GeoModel, Inc. conducts ground penetrating radar surveys using a SIR-2 or SIR-3000 digital control unit and various antennas with frequencies ranging from 200 to 1,500 MHz. The GeoModel, Inc. principals have over 50 years of combined experience and conduct GPR surveys nationwide.

 


Ground Penetrating Radar Applications

ground radar underground 4-way scan for utility locationpipes and utilities 4-way scan
ground penetrating radar for USTtank (UST) and drum location
GPR underground scanning for concreteconcrete and rebar imaging and inspection
ground radar for sinkholessinkholes
ground penetrating radar for geologygeology (bedrock) and geologic hazards
landfills and burial trenches
GPR for gravesitescemetery and grave location surveys
ground radar for archaeologyarchaeological studies

 


Where do GeoModel, Inc. is interviewed by David Ensor of CNN about ground penetrating radar (gpr)and GeoModel, Inc. is interviewed by Greta Van Susteren of Fox News about ground radar (gpr) get their information on ground penetrating radar?


Ground Penetrating Radar

GeoModel, Inc. is registered with the FCC and uses only FCC-approved GPR equipment

Ground penetrating radar (GPR) produces an underground, cross-sectional, two-dimensional image scan of the soils and subsurface features. Three-dimensional GPR images, such as the one below, can be produced using raw field data and post-processing software.

GeoModel ground penetrating radar system3-D image of underground pipes from ground penetrating radar (GPR) data obtained by GeoModel, Inc. with a 4-way scan

 

GeoModel, Inc. conducts ground penetrating radar (GPR) surveys using antennas with various frequencies. Depths of GPR underground scans can be as deep as 25 to 35 feet (8 to 11 meters) in sandy or silty soils, using a low frequency ground penetrating radar antenna.

A higher frequency antenna can examine the near surface, from 0 to 12 feet (0 to 3.6 meters), in greater detail. The ground penetrating radar signal does not go as deep (as little as 1 to 3 feet) in clayey soils.

 


Shallow Ground Penetrating Radar Surveys

Shallow ground penetrating radar surveys are conducted by one person, hand-towing or ATV-towing the antenna, and can examine the near subsurface from 0 to 12 feet (0 to 3.6 meters) below the ground surface.

Hand-towed GPRground penetrating radar of buried pipes

 

Applications for a shallow ground penetrating radar survey include locating pipelines and utilities using a 4-way scan, locating underground storage tanks (USTs) and drums, inspecting concrete, detecting rebar, locating unmarked gravesites, and conducting archaeological studies.

 

aerial photograph of ground radar and EM utility location survey areaAs-built utility map based on ground penetrating radar (GPR) data and metal detection (EM) data obtained by GeoModel, Inc.aerial photograph of same GPR and EM GeoModel, Inc. survey area

Before GeoModel, Inc. survey (left), GeoModel, Inc. As-built utility map (center), and area after construction (right)

 


Deep Ground Penetrating Radar Surveys

Deep ground penetrating radar underground scanning surveys are conducted with a low frequency GPR antenna, such as a 200-MHz antenna that can reach depths of up to 35 feet in sandy soils.

Applications for deep ground penetrating radar include landfill and burial trench delineation, geology and bedrock depth studies, and karst and sinkhole location.

Vehicle-towed GPRTrenches located by GeoModel, Inc. using ground penetrating radar

Top of Bedrock Profile located using ground radar by GeoModel, Inc.Sinkhole Located with ground penetrating radar (gpr) by GeoModel, Inc.

 


Concrete Inspection Surveys

GeoModel, Inc. can conduct ground penetrating radar (GPR) underground scanning of concrete to locate rebar, pipes, post tension bars, and conduits in concrete structures. Our scanning can also detect voids within concrete slabs and under concrete slabs.

Our ground penetrating radar scanning can inspect concrete walls, concrete floors, slabs, airport runways, tunnels, abutments, dams, and garages. Asphalt roads and surfaces can also be scanned.

concrete inspection survey using ground penetrating radarrebar in concrete and pipe in concrete located with ground radar

 


Cemetery and Grave Site Surveys

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

Gravesites located with ground penetrating radar by GeoModel, Inc.ground penetrating radar survey to locate gravesites, conducted by GeoModel, Inc.

 

GeoModel, Inc. uses GSSI (Geophysical Survey Systems, Inc.) GPR equipment to conduct its GPR survey services.


For a ground penetrating radar survey, click on your state below:

Map of the Untied States of America for ground penetrating radar projects

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e-mail: GeoModel e-mail for ground radargeomodel@geomodel.com

 


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