How Deep Does GPR Go?

If you are considering purchasing a ground penetrating radar system, you may be wondering “How Deep Does GPR go?”. We can help you answer this common question. However, the answer itself depends on three different factors: soil conditions, your system’s frequency range, and the size of the target you want to locate.

Additionally, another important factor is the specific GPR system used. We manufacture a wide variety of systems, because not every application requires the same frequency range. For example, someone looking to scan concrete does not need an antenna that can penetrate 60 feet underground.

Let’s examine the three major factors that affect a GPR system’s depth penetration capabilities to help answer how deep does GPR go. First, we want to briefly explain how GPR works.

How GPR Works: A Brief Primer

GPR (ground penetrating radar) systems are designed to image the subsurface across multiple terrains and soil conditions. Unlike more basic locating tools, GPR scans and images all the material beneath the soil within its range. This means that, as long as the signal is intact, it can play a key role in locating both conductive and nonconductive materials in addition to analyzing soil layers and any disturbances within.

Let’s use our GPRover system as an example. The operator pushes the system’s cart and antenna along the soil. In real time, the antenna transmits three separate signals that travel down into the soil. If the signal encounters and object, the signal is then bounced back up through the soil and returned to the antenna. When these pingbacks occur, they indicate the likely presence of an object or anomaly.

On the controller screen, these pingbacks are displayed as a change in the radar data; such as an arch-shaped hyperbola or a distortion of the image. Typically, the narrower and higher an arch, the smaller and rounder the object (like a fiber optic cable). If the arch is broader and flatter, that indicates a larger buried object like a septic tank. Something like a jagged distortion in the data may indicate a change in soil structure, such as the location of a trench.

Using our GPR software, the system operator can create datasets that image objects and changes to soil structure and record their locations via GPS. In turn, this provides a common reference point for other stakeholders for future digs in the same area.

Now that we’re all on the same page regarding how GPR works, let’s begin looking at the factors that impact how deep GPR can go.

Factor 1: Soil Conditions

Soil conditions have the greatest impact on the quality of your data. This is because the material you are surveying can either quickly absorb the antenna’s output or allow for a deeper penetration through the earth. The soil’s dielectric properties affect the depth that the energy can travel. If the operator is scanning over a highly dielectric soil like dense, wet clay, the signal will dissipate more quickly. In these conditions, a 250 MHz will only travel about 14 ft. (4.5m). Conversely, a low-dielectric soil will enable the same antenna to transmit a frequency that can travel down 30 ft. (9m) or more.

For operators that have to navigate a variety of soil conditions, we recommend using one of our triple frequency range systems like the Quantum Imager or GPRover. These systems have triple frequency range capabilities with antennas that transmit three separate signals simultaneously at low, middle, and high frequencies. This results in a high-quality read of the soil at multiple depths and resolutions for a clearer image of the subsurface.

Factor 2: Antenna Frequency

When considering how deep does GPR go, your specific needs play a major role in selecting the right system. You need to choose an antenna that can reach the depths you intend to scan that can match the field conditions you’re working in.

Here is a brief overview of how deep certain antennas can travel through different soil conditions:

Antenna Center Frequency (MHz)	Approx. Depth in Dense, Wet Clay	Approx. Depth in Clean, Dry Sand
100 MHz	40 ft. (12m)	100 ft.+ (30m)
250 MHz	14 ft. (4.5m)	30 ft. (9m)
500 MHz	6 ft. (1.8m)	14.5 ft. (5m)
1000 MHz	2 ft. (60cm)	6 ft. (1.8m)
2000 MHz	0.5 ft. (15cm)	2 ft. (60cm)

Implementing the right antenna solution for your specific application is critical to delivering the results you are looking for. Here is a simplified graphic if you would like a visual representation of which systems would work best for your needs:

Factor 3: The Size of the Target

Simply put: bigger objects reflect more energy. Keep this in mind when determining the approximate size of the object you are scanning for with a GPR system. The larger and closer to the surface the object is, the more energy it will reflect. The narrower and deeper the object is, depending on soil and antenna, the harder it might be to locate if the field conditions are not favorable.