Ground Penetrating Radar
Ground Penetrating Radar, also known as GPR, is a means of generating a profile of subsurface structures non-destructively. Ground penetrating radar is a geophysical method that uses radar pulses to image the subsurface. This non-destructive method uses electromagnetic radiation waves and detects the reflected signals from subsurface structures. What GPR does is produces and image of any underground features which are used to identify the location and depth of buried cables, items, and structures. The images also aid in determining soil type, structure, and the condition of everything.
The GPR device is an essential tool in The Underground Detective arsenal, requiring years of experience to correctly interpret its results.
How It’s Done
Since the soil does not have to be disturbed, GPR is a safe and cost effective way to identify underground unknowns. GPR units consist of an antenna transmits high frequency radio wave pulses which is dragged or rolled over the soil in a cart and a video screen and/or data logger to record all of the signals received.
GPR Variables
Although GPR is very useful for scanning larger area masses and for determining the location and depth of previously unknown objects or soil conditions, it does have limitations that must be taken into consideration.
Using GPR
GPR is used in a number of odd jobs, but the most common calls we receive request help with locating and searching for:
- Metallic and non-metallic pipes
- Underground storage tanks (UST)
- Trenches
- Grave sites
- Concrete scanning
GPR is used on the majority of our jobs to ensure the best utility knowledge along with your safety. We have used it numerous times locating unmarked graves and even to discover a time capsule!
Soil Conductivity
This is a measure of how well an electromagnetic signal may pass through an unknown material. If the soil conductivity is low, the signal can travel farther than soil that has high conductivity soils, which limit and hinder GPR radar from properly penetrating the soil. Look at this as whether the GPR technology can clearly “see” unknown objects below the soil. Below you will find examples of each soil.
Low Conductivity Soils Include:
- Dry Soil
- Sand
- Granite Soil
High Conductivity Soils Include:
- Clay
- Shale
- Soils saturated with water
Antenna Frequency
The frequency of GPR antennas affect the depth at which they can “see” and how much detail they can map out.
Low Frequency Antennas can penetrate deep into soils, but produce low image resolutions. This is typically useful for identifying soil geologies and structures such as soil stratification, sinkholes, and fractures.
High Frequency Antennas can only penetrate a short distance into the soils, but produces very detailed images of the soil and unknown utilities and objects.
Pipe and/or Cable Diameter
Just as GPR signals cannot always penetrate all soil types, GPR cannot always capture materials that are small in diameter. For instance, if a pipe or cable is buried very deeply or is less than 4 inches in diameter, GPR technology may not be able to locate them.
The Underground Detective can help you with all of you GPR needs. Request a quote to begin your project!
