Ground-Penetrating Radar for Archaeology by Conyers Lawrence B

Author:Conyers, Lawrence B. [Conyers, Lawrence B.]
Language: eng
Format: epub
Publisher: AltaMira Press
Published: 2013-10-14T16:00:00+00:00

Figure 5.2

At least three waves are recorded in CMP and WARR tests: the air wave that travels in air from transmitting to receiving antennas, the ground wave that moves along the interface between the ground and the air, and one or more reflected (and sometimes refracted) waves that move within the ground.

In both WARR and CMP tests, radar energy is sent from one antenna to the other as they are moved an increasing distance apart. Individual reflection traces are usually collected (and often stacked to improve their quality) in step mode for this type of test. The radar waves moving between the antennas will pass through both the air and near-surface layers of the ground and be received at the other (figure 5.2). If the distance of separation is known and the radar wave travel paths can be deduced, the arriving waves can be measured in time, and a series of velocity measurements of different layers in the ground can potentially be calculated. In the CMP method, both antennas are first placed next to each other on the ground, and one reflection trace is collected. There may be three or more wave arrivals collected at this location: one that travels in air, one along the air–ground interface and possibly more that are reflected and refracted from buried interfaces in the ground. The antennas are then separated a measured distance (10 centimeters, perhaps), and another reflection trace is recorded (figure 5.3). This collection procedure is repeated many times until the antennas are separated by as much as 5 or 10 meters. Energy will continue to travel a number of paths between the two antennas, and if the wave arrivals that have traveled within the ground can be identified, and the distance between the two antennas is known, velocity can be calculated. The same type of recording can also be made in continuous data acquisition with the imposition of fiducial marks to yield distance as measured along a tape measure on the ground.

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