This series has previously addressed magnetometry and electromagnetic induction. While both of these sensing techniques are frequently used by archeologists and treasure hunters to find objects, they are often combined with ground penetrating radar (GPR) to improve the search results. Compared to other commonly available geophysical methods, GPR is the only one that provides true depth information.
GPR works by transmitting a high frequency radio signal into the ground and detecting the reflected signals returned to the receiver. The results are displayed and stored on digital media. Archeologists consider GPR to be the most accurate, highest resolution geophysical technology.
In low conductivity soils such as dry sand or granite, GPR can reach depths of up to 100 feet (30 meters). In contrast, moist clays, shale, and other high conductivity materials can decrease its capability to 3 feet (1 meter) or less.
Combined with other sensing techniques, GPR can be used for sensing both large and smaller areas. In large multi-acre areas, GPR data can provide a high-resolution map of what an archeological site might have looked like when it was occupied.
For smaller areas, especially when a target has been identified, GPR can be used to get more definitive information of specific features such as size and depth, and details regarding if an area is filled with rubble or clean material.
For locating buried treasure, GPR can provide the depth of identified anomalies prior to digging.
The next article in this series will discuss LiDAR (Light Detection and Ranging), another technique often combined with either or EMI or magnetometry.