Geophysics at Fort Hollingsworth
by Peter Quantock
In recent years, geophysical survey has become an increasingly popular archaeological tool in Maryland. Archaeologists at sites such as Port Tobacco, Nottingham, and Benedict conducted magnetometry and ground-penetrating radar surveys as part of their investigations. In Jim Gibb’s 5 part series about Fort Hollingsworth on this blog, he talked briefly about the geophysical techniques that were used to help locate the fort.
Today, I’m going to give you a little more information on the ground-penetrating radar (GPR) survey conducted at the site through images of the data. GPR is a technique that collects and records information about the subsurface. It involves the transmission of high frequency radar pulses from a surface antenna into the ground. This data is converted into vertical profiles and plan view maps to aid in interpretation.
GPR Gear: GSSI SIR-3000 with 400MHz dual antenna and survey wheel used to conduct the survey at Fort Hollingsworth.
In March 2012, with the help of ASM members and other volunteers, I conducted a GPR survey over top of the magnetometer survey I did the year before. The goal was to find the trench used at Fort Hollingsworth. And we were successful! Read all about it in the "Finding Fort Hollingsworth" series on this blog.
To interpret GPR data we first go to the vertical profile, which allows us to look at the depth of features in the ground. Below is an example of a vertical profile collected at the site. This profile runs north south within the larger grid. It looks like a bunch of sharp, squiggly lines, doesn’t it?