Atkinson-Noland & Associates, in collaboration with the National Park Service, DHM Design, and Silman recently completed an investigation using Surface Penetrating Radar (SPR) on the walls of the historic Fort Wood. The former fort, now used as the base of the Statue of Liberty, was constructed in 1807 and is an 11-pointed star with approximately 26-foot-tall walls. As part of the rehabilitation and preservation plan, ANA’s investigation aimed to evaluate the subsurface conditions to determine if low-pressure injection grouting or other remediation would be beneficial and effective. ANA had to overcome challenges related to the height, thickness, and surface roughness of the walls to collect effective SPR scans. Using a custom pulley system to lower the radar unit at a constant speed, three-dimensional mapping of the voids within the walls along with an estimation of their volumes was completed successfully.