EM304 Water Column Sonar Data Collected During EX2305

From August 1 - August 17, 2023 (Unalaska, Alaska to Kodiak, Alaska), NOAA Ocean Exploration completed the expedition Seascape Alaska 4: Gulf of Alaska Mapping (EX2305). Mapping operations during this 17-day expedition aided in closing bathymetric gaps off the coast of the Aleutian Islands and in the Gulf of Alaska. EX2305 collected 23,591 square kilometers of seafloor bathymetry within the U.S. Exclusive Economic Zone deeper than 200 m. During mapping operations, NOAA Ocean Exploration simultaneously collected EM 304 multibeam sonar bathymetry observations and Simrad EK60/EK80 split-beam fisheries sonar observations of biologic material in the water column, as well as Knudsen 3260 sub-bottom profiler observations of sub-seafloor geologic structure and sediment. A focused survey region targeted seamounts in the Gulf of Alaska. During the expedition, an EK calibration was completed for the 18, 38, 70, 120, and 200 kHz frequency sonars. The exploratory mapping operations conducted during this cruise will provide initial characterization of the region, as well as data to support further exploration. All data associated with this expedition will be archived within 120 days of the end of the expedition and will be publicly available through the NOAA Archives.