Ground- Penetrating Radar and GPS
Ground-penetrating radar (GPR) is a method of using radar pulses to produce images of the subsurface. Electromagnetic radiation is able to detect reflected signals from subsurface structures. The GPR transmitter system contains antennas that transmit and receive radio frequency waves. The GPR system is portable, it sits on wheels and is pushed over the study area. Radio frequency waves are then penetrated into the surface that is being investigated. The GPR transmitter correlates to a screen that displays the results of the radio wave penetrations. As the waves are being sent into the surface, the signal mostly dissipates. However, a percentage of the signal comes back and is received by the antenna. The return signal provides data that is displayed on the screen. The results from the antenna can be recorded and later interpreted by the user. The recorded images show the size and depths of the objects under the ground’s surface and where they are located. The GPR is primarily used to show differences in material composition. Objects that are buried beneath the ground surface will appear different than the surrounding soil compositions. This is helpful in determining archaeological records and evidence of past architectural features. Although the GPR can detect the presence of objects under the ground surface, it does have its limitations. It cannot determine depth or vertical profiles of objects. GPR often picks up the presence of more modern innovations, like pipes and cables as well as tree roots and other naturally occurring disruption. Due to preliminary investigation of the site we knew that there was the possibility of finding a path that connected from the original house of James Monroe to the Academical Village. We used the GPR to determine evidence of the path’s presence. Starting at the landscape closest to the original doorway of the Law Office, we traced the ground horizontally to see if the GPR would find evidence of the path. In order to counteract the error of modern improvements in the ground we used an updated copy of the utilities map to ensure that we were not picking up signals from pipes or cables. When we found something of interest on display, we placed a flag into the earth where the point correlated with the GPR results.
We surveyed the front of the Monroe Hill landscape using GPR, and placed flags into the points of interest throughout. After we completed the GPR process, we digitally documented the flagged areas using Global Positioning System (GPS) coordinates. We used an advanced GPS receiver to record the precise locations of the features we picked up using the GPR. The GPS points were recorded and then transferred to Geographic Information System (GIS) Once the points are in GIS they can be mapped and further analyzed.
GPR Findings:
