GPR:

Ground Penetrating Radar (GPR) locates using antennas that emit and receive pulses of electromagnetic energy through a medium such as the ground or concrete.

As the radar reflects off of materials it 'echo locates' materials or objects of different electromagnetic conductivity within a matrix, for instance, a pipeline, storage tank, contaminant or re-bar in a matrix of soil or concrete. This reflection is processed and then displayed as a time slice along a horizontal transect line with the reflection time related to the depth of an object.

Objects within the matrix, such a pipeline or re-bar, show up quite clearly as hyperbolas with only discrete differences based on their relative conductivities. A number of these transect lines need to be acquired to gain a precise location of the target in one direction. The same process must be done in the perpendicular direction to get a full picture of where objects are in the matrix. The reflected energy pulses are acquired only in a narrow line directly below where the transects are taken and the positions of objects have to be correlated from line to line. The data can also be utilized in a 3-D program to yield a sub-surface profile of the area surveyed.

Global Positioning System (GPS):

GPS is a satellite based positioning system that provides precise location measurements. A GPS can be combined with a Ground Penetrating Radar (GPR) unit to tie the radar data to known geographic coordinates. By conducting a GPR survey in a grid pattern, Universal Transverse Mercator(UTM) coordinates for target locations can be obtained. UTM is a type of mapping coordinate system. The GPS data then allows the survey results to be exported to either a Geographic Information System(GIS) or Computer Aided Drafting(CAD) system to produce a final product that is accurate, clear, and capable of being combined with other data sets.