NOT SUCH AN EASY TARGET: USING GPR TO LOCATE MORTARS BURIED ON WEST POINT'S PARADE FIELD

From at least 1902 to 1931, cadets at the United States Military Academy trained on two 12-inch coastal artillery mortars at Battery Byrne. Battery Byrne was the remnants of a kettle lake named Execution Hollow, located on the edge of West Point's parade field. After failed efforts to move the mortars, the tubes and carriages were buried in-place in 1931, where they remain at a depth of anywhere from two to six meters.

We used ground penetrating radar (GPR) to attempt to locate the mortars. Locating a 30,000 pound iron mortar mounted on an 85,000 pound carriage, buried a few meters underground, would normally be a simple task, but here we contend with cultural noise that interfered with our efforts. Battery Byrne was filled and leveled in order to expand the cadet parade field in 1931. The fill consisted of dirt and granitic gneiss boulders from nearby excavations, so the subsurface has little recognizable stratification, nor soil profiles, nor homogenous material surfaces. Constructed on top of this 1931 filled surface are concrete pads supporting tall metal bleachers. Historical records of the mortar burial are sketchy and are not clear whether there are two mortars or just one (rumors tell of a salvage operation for scrap metal during World War II).

Our case study combined a detailed photogrammetry survey, georeferencing aerial photos from 1922 with current imagery, review of exploratory GPR surveys completed in 2002 with 200 MHz antennae, and a new GPR survey using both 225 and 110 MHz antennae with a Sensors & Software pulseEKKO 1000. The GPR survey was enticing due to the attractive, seemingly “easy” target. We found that ample knowledge of the target can sometimes compensate for survey challenges due to surface interference from cultural noise, but not always. Additionally, completing and recording a detailed survey of this site created an exciting and immediately accessible laboratory exercise for West Point cadets interested in geophysics.