How Does a Ground Penetrating Radar Work?

Ground Penetrating Radar Basics

Ground penetrating radar (GPR) is a method of determining what is under the surface of the ground without digging it up. GPR can detect underground water, rock, buried ruins and many other types of objects. It is used extensively in archaeology, forensics and even construction to quickly and inexpensively gather subterranean information.

How Ground Penetrating Radar Works

A high-frequency signal--either a radio wave or a microwave--is shot directly at the ground by a transmitter. This signal will travel through the ground until the consistency of the earth changes. When it comes across a different sort of object, some of the signal passes on and some of it is reflected back to an antenna. For example, if a GPR wave going through sand encounters a big block of limestone, some of it will be reflected back to an antenna.

Constructing an Image

Radar moves at the speed of light. It is very fast, but not instantaneous. When the signal is reflected back, a computer measures how long it took to make the trip there and back. From this, the computer calculates how deep the buried object is. The GPR machine will be dragged back and forth over the ground, making thousands of measurements in an area. A computer puts these together to make a 3D model of the objects buried under the ground.