Ground Penetrating Radar (GPR)
Ground Penetrating Radar 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 a buried cellars or pits, or solid objects like walls or building foundations, would contrast with the surrounding soil and show up as anomalies in the data.
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.
In Action: GPR was used at Topper to create a map of underground quarry deposits.