Not Such an Easy Target: A Student Case Study using Ground Penetrating Radar to Locate Buried Mortars at West Point

One, or possibly two, of the 12-inch coastal artillery mortars used for cadet artillery instruction between 1902 and 1931 remain buried roughly two to six meters below the surface of the northern edge of the Plain at the United States Military Academy at West Point, New York. This survey used a Sensors and Software PulseEKKO 1000 Ground Penetrating Radar (GPR), 225 MHz antennae, together with geo-referenced imagery to attempt to locate these mortars. The intrinsic value of 132 tons of buried iron, the historic value of the mortars, and sheer curiosity provided the impetus for this study. Geo-referenced aerial photography of Battery Byrne provided a starting point for the search, and we developed a data collection grid to estimate the most likely location. We collected data in conjunction with independent study classes from September 2007 through April 2008, collecting a total of 7,690 GPR traces. After processing initial data with EkkoView and EkkoMapper, we found a distinct hyperbola at Trace 386 of Line 16. We then constructed a tighter grid to characterize our point in higher resolution, but the reflection we identified may be too shallow to be the first mortar. For the second mortar, we focused on a location identified from a 2002 GPR survey, which indicated a mortar near the corner of a gravel pit on the grass of the Plain. The data indicated a small hyperbola shape in the East-West transect of Line 12, so we designed a second tighter grid to further investigate. Again, the results were not as conclusive as we had hoped. Additional research with another ground-truthing method, such as a magnetic or a gravity survey, could validate our findings. This survey has opened the way for future work. More GPR data with a different frequency would be beneficial, preferably 110 MHz to achieve greater penetration. Alternate methods of near surface geophysics would be very valuable, such as magnetic, gravity, or even seismic refraction. Additionally, a partnership with the Department of Civil Engineering could determine the costs, benefits, and feasibility of an excavation project. The West Point Historian may eventually want to erect a plaque describing the historical importance of Battery Byrne for the artillery instruction of cadets. Finally, locating these mortars would provide an interesting geophysics laboratory exercise for future West Point cadets in science and engineering classes.