Assessing the Accuracy of Underwater Photogrammetry for Archaeology: A Comparison of Structure from Motion Photogrammetry and Real Time Kinematic Survey at the East Key Construction Wreck

The National Park Service (NPS) Submerged Resources Center (SRC) documented the East Key Construction Wreck in Dry Tortugas National Park using Structure from Motion photogrammetry, traditional archaeological hand mapping, and real time kinematic GPS (Global Positioning System) survey to test the accuracy of and establish a baseline "worst case scenario" for 3D models created with NPS SRC's tri-camera photogrammetry system, SeaArray. The data sets were compared using statistical analysis to determine accuracy and precision. Additionally, the team evaluated the amount of time and resources necessary to produce an acceptably accurate photogrammetry model that can be used for a variety of archaeological functions, including site monitoring and interpretation. Through statistical analysis, the team determined that, in the worst case scenario, in its current iteration, photogrammetry models created with SeaArray have a margin of error of 5.29 cm at a site over 84 m in length and 65 m in width. This paper discusses the design of the survey, acquisition and processing of data, analysis, issues encountered, and plans to improve the accuracy of the SeaArray photogrammetry system.