GPR instuments and examples

All ground penetrating radar (GPR) instruments have three main components: Transmitter and receiver that are directly connected to an antenna, and a control unit. The transmitting antenna radiates a short high-frequency EM pulse into the ground, where it is refracted, diffracted and reflected primarily as it encounters changes in dielectric permittivity and electric conductivity. See Appendix A for list of Electrical Properties of Geological Media.

The propagation of a radar signal depends mainly on the electrical properties of the subsurface materials. If the constituent material of a object (an underground storage tank for example) is expected to be metal, and metal has a dialect constant considered infinite, metals are generally recorded as “loud” reflections or diffractions depending on the geometry of the object. Waves that are scattered back toward the surface induce a signal in the receiving antenna, and are recorded as digitized signals for display and further analysis.  A limiting factor of GPR recordings is the conductivity of the surrounding medium. General rule of thumb: the penetration depth of GPR in meters is ~40/conductivity where conductivity is in milliSeimens per meter.  So, if the surrounding medium has conductivity of 20 mS/m, we should expect GPR depth of penetration to be approximately 2 meters.

Some examples

GPR Bathymetry : Measuring depth of a frozen lake in the Northwest Territory.

ERT and GPR : comparing electrical resistivity tomography (ERT) and ground penetrating radar in a shallow lithology (~4m) investigation, Hinton area, Alberta.

GPR_deep: various examples where we have gone exploring for targets at depths beyond 3 m.

GPR examples: a myriad of examples looking at different applications (from looking for graves to locating missing underground storage tanks).