Basic Principal of GPR

Ground Penetrating Radar (GPR) utilizes a high frequency radio signal which is transmitted into the ground in pulses. The reflected signals bounce back to the receiver and stored on digital media. The internal computer measures the time it took for a pulse to travel to and from the target and calculates its depth and location. The reflected signals are interpreted by the software and displayed on the digital video display panel.

gpr basic principal
Subsurface GPR Data Collection

To find the location and depth of a target, buried below ground, various configurations of GPR systems are used to collect data. The type of GPR system required is dependent on soil conditions, depth and size of the target to be located. The GPR system emits and receives reflected pulses up to a thousand times per second. These signals are viewed by the field technician for immediate analysis. This data is stored in the system and can be transferred to a computer for additional data analysis if required.

gpr data collection
GPR Concrete Scanning

To locate rebar, conduits and post-tension cables in a concrete slab a high frequency GPR system is used. To assess the thickness of concrete slab the data can be collected in simple line scans. However, scanning in a grid format will produce a map of any targets located in the concrete. This method allows us to look at virtual slices in the slab to determine the position and depth of the objects and create a 3D map of the results.

gpr concrete data collection
GPR Data Analysis

GPR signals can travel through many different materials. Different types of soil, fill material, concrete (each with varying amounts of water saturation), will have different conductive and dielectric properties that affect the GPR waves. This will affect the GPR data interpretation. The data images displayed on the GPR screen require a technician with field experience to interpret the results displayed in order to accurately determine the findings.

gpr data analysis
How Deep Can GPR Go?

This is one of the most commonly asked questions regarding this technology. In many cases the estimated depth range is based on the subsurface material and the GPR antenna frequency. For applications which require higher resolution, such as locating conduits or rebar in concrete, a higher frequency GPR system (1,000 MHz) is used. This produces high resolution data to approximately 24 inches in depth. Locating targets in ground soil requires deeper penetration and a lower frequency (12.5 MHz to 500 MHz). Depending on the subsurface material the depth of penetration can be from a few inches to thousands of feet (as indicated in the chart).

gpr-depth-chart

* Contact us if you require additional information regarding ground penetrating radar technology.

Ground Penetrating Radar (GPR) Subsurface Imaging Services for Underground Locating Applications by Global GPR Services Inc.