Autonomous Underwater Vehicle–Based Hydrographic Sampling

Abstract An autonomous underwater vehicle (AUV), the U.S. Navy’s Large Diameter Unmanned Underwater Vehicle (LDUUV), was used as a stable platform for rapid, repeated, near-synoptic CTD measurements of estuarine variability in Narragansett Bay. Surveys were made in lawnmower-like patterns at middepth to obtain horizontal profiles and maps, and in vertical yo-yo patterns to obtain vertical profiles. These observations were ground-truthed using standard CTDs on the fixed position of the launch cage and on ship-based surveys around the perimeter of the study area before and after the runs. For the horizontal surveys, a comparison of temperature and salinity time series from the LDUUV and the launch cage CTDs shows that differences are within the range of lateral variability around the study area observed at run depth from the ship. For the yo-yo surveys, a comparison of LDUUV CTD and standard CTD profiles shows indications of hysteresis in the vehicle-obtained data, which can be minimized with improved sampl...