How Ground Penetrating Radar Works

Ground Penetrating Radar (GPR) uses pulses of radio waves to penetrate into the materials under evaluation. Each pulse is triggered by an odometer wheel traveling a measured distance. The reflected wave of each pulse is captured by the video logger as one trace. Each trace provides information on the layers the radio wave has penetrated. The amplitudes of the reflected wave is dependent on the electrical conductivity of every material in its path and its distance from the surface. Many traces make up an entire scan along a surface. Depending on the requirements, these scans can be used directly in the field to locate embedded materials or can be stored digitally for subsequent imaging analysis

GPR Equipment

3D Imaging of GPR Scans

3D imaging can substantially improve the visualization and hence interpretation of GPR scans. The individual vertical scans are lined up in the computer and horizontal slices are taken across the composite data set. Slices can be obtained throughout the depth of the composite scans to provide information at various selected depths

Schematic example of 3D slice of scanned data

Is the Frequency Used Important?

The frequency of the antenna used is all important and its proper selection is often the difference between success or failure of this technology. The shorter the wave length used, the less the depth of penetration, but it is compensated by more detail obtained in each trace. GPR antennas used for structural surveys should have wave lengths of 1000 to 1500 MHz. Other system use wave lengths of 500 MHz and 250 MHz and are more suited to detecting underground utilities and the surveying of geophysical layering for example

How Deep Can it Scan?

This depends on the antennae used and the material through which it is traveling. The high frequency waves used to evaluate structures are influenced by the dielectric properties of materials and the presence of free ions which can scatter the reflected waves. Typically with the antenna used to survey structures, a maximum depth of penetration of about 2 meters can be expected.

Is it Safe?

GPR is very safe. It uses radio waves of similar frequency to cellular phones but with significantly reduced energy levels.

Scan Examples

3D Concrete Examples

3D Masonry Examples