Geophysical Technique

Ground-Penetrating Radar (GPR)

Ground-Penetrating Radar (GPR) uses electromagnetic radar waves to map boundaries between contrasting underground materials. GPR is handy for measuring changes in soil density that could indicate buried features. For example, open spaces like buried cellars or pits, or solid objects like walls or building foundations show up as anomalies in the data because they contrast with the surrounding soil.

Pros: Areas that have been disturbed would have a different reading than the ground around it, leaving old trenches, roadways, and pits visible under the soil for a long time.

Cons: Tree roots or other shallow objects can obscure deeper archaeological remains.

See What Meg Sees: Instructions for Interpreting the Data

Using the tool below, click on individual grids for a closer look at the GPR data Meg and her team gathered at Camp Lawton. You can toggle between an arieal view of the landsape, the map of the data only, and then read Meg's interpertation of each of the data points as you learn more about what each grid reveals. Each grid you click on will become highlighted.

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MEET THE TEAM

Bryan Haley

Bryan Haley

Archaeological Geophysist

Dr. Duncan McKinnon

Dr. Duncan McKinnon

Geophysics Specialist

The GPR image shows a single "slice" of data collected. Each slice is approximately 0.25m thick at a depth of about 0.5 m. This entire image is created from stacking the individual profiles (or slices) of GPR data, which are vertical scans. GPR essentially slices down into the earth to produce horizontal plan maps. The map best demonstrates how the stockade wall trench appeared in the GPR data that finally enabled us to locate the southwestern corner of the prison enclosure wall.

GPR was only one of the survey methods we used around the site at Camp Lawton. We used it specifically to identify the location of the stockade wall trench. This however, did not prove easy. We surveyed a large area and saw very little signs of the trench in the data. Fortunately, in the end, I was able to place two backhoe trenches down over the location of the stockade wall trench, but it was no easy process, nor was the wall trench a strong "anomaly" in the geophysical data.

INTERPRET MORE DATA

Magnetometry

Magnetometry

Magnetic survey measures the variation of magnetic fields of the earth.

Resistivity

Resistivity

Resistance survey measures the subsurface variation in soil.

Magnetic Susceptibility

Magnetic Susceptibility

This survey induces an electromagnetic field into the earth through a transmitting coil.