What is Ground Penetrating Radar?
Ground penetrating radar is a form of radar which is designed for subsurface imaging. In other words, it’s radar which can be used to see things underground, in contrast with the radar used to identify features in the ocean or to analyze walls to determine what might be on the other side. There are a number of applications for ground penetrating radar, and several firms make a variety of radar units designed for this purpose. This type of specialized radar works a lot like regular radar. The radar unit has a sending antenna which sends out pulses of sound, and a receiving antenna, which picks up those pulses when they bounce off objects underground. The returned pulses can be used to construct an image of what is underground, because they will vary depending on the depth and composition of buried objects. Several factors influence the usefulness of ground penetrating radar. The first is the nature of the ground being examined, and what people are looking for; subtle geological differen
Ground penetrating radar (GPR) is a tool for indirectly looking at underground objects (such as graves), gravel and sand layers, and other underground structures. The information or data received by GPR is like an x-ray or map of the underground. In fact, GPR uses electromagnetic (EM) waves, as x-ray machines do, but GPR uses radio waves, which have a longer wavelength (see Figure 1). The wavelength, or the length of one wave, is the fundamental difference between the forms of electromagnetic energy. For example, the wavelength of x-rays range from about 10 billionths of a meter to about 10 trillionths of a meter, whereas radio waves can be a few meters long. GPR antennae To collect GPR data, two antennae are repeatedly placed along the ground surface at a constant interval. Unlike a radio or TV antenna, GPR antennae usually look like two skis that vary in length from less than meter long to 4 or more meters long as shown in Figure 2. Different length antennae send different frequency
Ground penetrating radar utilizes radio frequency waves to detect subsurface features. An antenna, which is pulled across the surface of the ground, transmits a signal that penetrates the subsurface. As this signal passes through various layers of sediment, it is reflected back up and received by the antenna. The “signals” that are picked up are displayed graphically on a computer. GPR s operate at frequencies between 20 and 1000 MHz. The lower frequencies give lower resolution, penetrating approximately 30 m. Higher frequencies show better resolution, but do not penetrate as far.
