Introduction to Ground Penetrating Radar (GPR)

See also: GPR in Volcanic Environments

Introduction

Ground Penetrating Radar (GPR) is a non-invasive, sub-surface imaging technique that has been successfully used in a wide range of geological, geotechnical, hydrological, environmental and archaeological applications. The GPR technique uses an antenna pair (transmitter and receiver separated by a small fixed distance) to send short pulses of electromagnetic energy into the subsurface and then record the returning signals. Depending on the application, different antennas are used (ranging from about 10 MHz to a few GHz) with, in general, low frequency antennae providing greater penetration, but lower resolution, and high frequency antennae having limited penetration but higher resolution. GPR is best suited for ‘dry’ materials (e.g., sandy soils, limestone, granite) but can work well in saturated environments. Unfortunately, GPR does not work well in clay-rich soils, or saline environments, where the penetration depth is severely compromised.

GPR Data collection GPR Principles

GPR data acquisition.

GPR principle: EM energy is sent into the ground by the transmitter antenna (Tx) and reflected back toward the receiver (Rx) at any subsurface discontinuity, such as the top and bottom of a buried object (a and c) or a geological interface (b).

Data collected in the field usually needs some degree of post-collection data processing in order to filter out unwanted noise and enhance the visibility of weak signals. The resultant GPR sections (or radargrams) represent a two-dimensional ‘cross-sectional’ image of the sub-surface that, with skill, can be interpreted in order to reveal the nature of the sub-surface features.

See also: GPR in Volcanic Environments