On Wednesday, July 19, the class at Birdwood used ground penetrating radar (GRP), to explore below the grass and dirt of three different areas of the Birdwood estate. GPR allows us to see how deep, the size and the composition of both items and disturbances in the soil. The machine we used was calibrated to read the type of soil around the house (Cecil loam). They can also be programed to read a range of other materials and compositions like clay or sand. Then, GPR works by slowly walking the lawnmower-like machine over a plot, as it sends radar pulses which return shapes that bounce off what’s below the machine. It can even show if soil has been disturbed. A screen on the machine shows the returns in three different channels, from one-three feet deep, up to eight feet deep, and up to sixteen feet deep. If anything shows up, it will appear as a parabola, signaling us to continue to focus on a particular area. With the help of Mathew Bartley and two interns from the UVA Facilities, we were able to scan areas around the carriage house, the lawn area roughly behind/adjacent to the smokehouse, and around and between the kitchen and smokehouse.
We began the morning beside the carriage house where Matthew showed us how to start initial scans of a piece of land, making passes at right angles in the selected field. At first he did sweeps about four or five feet apart, simply to see what is under the soil, then adjusted his sweeps according to returns we received on the screen, be it an anomaly, a pipe, or something else. When something interesting was found, the spot was marked and then mapped GPS coordinates, which we can look at later to analyze for their significance to the site. While we were beside the carriage house, we found what we think to be pipes, a trench, and a clear slope in the soil. Before we started the next section, Matthew showed us plans for the field that is to be the parking lot, showing a network of sewage drainage pipes running perpendicular to the line of trees behind the house. We did find that network as we did scans of that area.
