From April 13 - May 4, 2024 (San Francisco, California to Honolulu, Hawai’i), NOAA Ocean Exploration conducted the 2024 Mapping Shakedown + High Seas Mapping expedition to test and calibrate the acoustic mapping and associated systems aboard the NOAAS Okeanos Explorer following a drydock period over the winter or 2023/2024. The primary focus of this expedition was to ensure readiness of all sensors and equipment for the 2024 field season. Shakedown and readiness operations included calibrations of the POS MV and Seapath positioning and attitude systems, geometric calibration of the EM304 MKII multibeam echosounder, multibeam swath accuracy assessment at expected operational depths for this field season, speed-noise tests, and calibrations of each of the EK60/80 split beam sonars.

Equipment Used: NOAA Ship Okeanos Explorer is equipped with a 26 kilohertz (kHz) Kongsberg EM 304 MKII multibeam sonar. The nominal transmit (TX) alongtrack beamwidth is 0.5°, and the nominal receive (RX) acrosstrack beamwidth is 1.0°. The system generates a 150° beam fan, containing 512 beams with up to 800 soundings per ping cycle when in high-density mode. In waters shallower than approximately 3,300 m the system is able to operate in dual-swath mode, where one nominal ping cycle includes two swaths, resulting in up to 1,600 soundings. Data are recorded using Kongsberg's Seafloor Information System (SIS) software. Collocated to the bathymetric data, bottom backscatter data were collected and stored within the raw files, both as beam-averaged backscatter values, and as full-time series values (snippets) within each beam. During standard data acquisition, the EM 304 multibeam sonar is synchronized with the other active sonars using the Kongsberg Synchronization Unit with the EM 304 multibeam sonar set as the master. Any changes in equipment setup for the year or expedition are detailed in the annual Readiness Report or associated Expedition Report, respectively. For general information about sub-bottom operations, please refer to the NOAA Ocean Exploration Mapping Procedures Manual. Calibrations: At the beginning of each field season, a multibeam geometric calibration (patch test) is conducted to resolve any angular misalignments of the EM 304 multibeam equipment. A patch test is also conducted if any multibeam equipment (e.g., transducers, IMU, antennas) is installed or disturbed. The patch test determines if there are any residual biases or errors in navigation timing, pitch, roll, and heading/yaw (and resolves each bias individually in that order). Whenever possible (and assuming reasonable values), the results of each test are applied in SIS prior to data collection for the following test. Calibration Reports are archived as supplemental documents to the annual Readiness Report throughout the year. A relative backscatter correction was performed in 2021, and the resulting gain values were uploaded to the processing unit. This procedure helps to normalize differences in backscatter values resulting from variable frequencies and pulse durations employed within sectors and among ping modes used during multibeam data acquisition. Acquisition Corrections: Real-time corrections to the data upon acquisition include the continuous application of surface sound speed obtained with a hull-mounted Reson SV-70 probe, and application of water column sound speed profiles obtained with Sippican Deep Blue Expendable Bathythermographs (XBTs) and/or Seabird CTD 9/11. Sound speed profiles are conducted every four hours, or more frequently as dictated by local oceanographic conditions (typically every two hours when operating in more dynamic areas). Reson sound speed values are constantly compared against secondarily derived sound speed values from the ship’s onboard thermosalinograph flow-through system as a quality assurance measure. Roll, pitch, and heave motion corrections are applied in real-time via a POS MV 320 version 5 or a Seapath-380, using Marine Star DGPS correctors. The motion and positioning unit used will be noted in the processing logs. No tidal corrections are applied to the raw or processed data. Multibeam data quality is monitored in real-time by acquisition watchstanders. Ship speed is adjusted to maintain data quality and sounding density as necessary. Line spacing is planned to ensure one-quarter to one-third swath-width overlap between lines, depending on the environmental conditions and impact on the quality of the outer swath regions. Angles are generally left open (70°/70°) during transits to maximize data collection and are adjusted on both the port and starboard sides to ensure the best data quality and coverage. If outer beams are returning obviously spurious soundings (e.g., due to attenuation or low

From May 14 - June 7, 2022 (Newport, Rhode Island to St. John's, Newfoundland), NOAA Ocean Exploration conducted mapping operations on the Charlie Gibbs Fracture Zone, aiding in closing bathymetric gaps within this region. EX-22-04 collected 46,250 square kilometers of bathymetry and associated water column data. 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. Additionally, a calibration of the EK60/EK80 transducers was completed. The exploratory mapping operations conducted during this cruise will provide initial characterization of the region, as well as data to support further exploration.

Equipment Used: NOAA Ship Okeanos Explorer is equipped with a 26 kilohertz (kHz) Kongsberg EM 304 MKII multibeam sonar. The nominal transmit (TX) alongtrack beamwidth is 0.5°, and the nominal receive (RX) acrosstrack beamwidth is 1.0°. The system generates a 150° beam fan, containing 512 beams with up to 800 soundings per ping cycle when in high-density mode. In waters shallower than approximately 3,300 m the system is able to operate in dual-swath mode, where one nominal ping cycle includes two swaths, resulting in up to 1,600 soundings. Data are recorded using Kongsberg's Seafloor Information System (SIS) software. Collocated to the bathymetric data, bottom backscatter data were collected and stored within the raw files, both as beam-averaged backscatter values, and as full-time series values (snippets) within each beam. During standard data acquisition, the EM 304 multibeam sonar is synchronized with the other active sonars using the Kongsberg Synchronization Unit with the EM 304 multibeam sonar set as the master. Any changes in equipment setup for the year or expedition are detailed in the annual Readiness Report or associated Expedition Report, respectively. For general information about sub-bottom operations, please refer to the NOAA Ocean Exploration Mapping Procedures Manual. Calibrations: At the beginning of each field season, a multibeam geometric calibration (patch test) is conducted to resolve any angular misalignments of the EM 304 multibeam equipment. A patch test is also conducted if any multibeam equipment (e.g., transducers, IMU, antennas) is installed or disturbed. The patch test determines if there are any residual biases or errors in navigation timing, pitch, roll, and heading/yaw (and resolves each bias individually in that order). Whenever possible (and assuming reasonable values), the results of each test are applied in SIS prior to data collection for the following test. Calibration Reports are archived as supplemental documents to the annual Readiness Report throughout the year. A relative backscatter correction was performed in 2021, and the resulting gain values were uploaded to the processing unit. This procedure helps to normalize differences in backscatter values resulting from variable frequencies and pulse durations employed within sectors and among ping modes used during multibeam data acquisition. Acquisition Corrections: Real-time corrections to the data upon acquisition include the continuous application of surface sound speed obtained with a hull-mounted Reson SV-70 probe, and application of water column sound speed profiles obtained with Sippican Deep Blue Expendable Bathythermographs (XBTs) and/or Seabird CTD 9/11. Sound speed profiles are conducted every four hours, or more frequently as dictated by local oceanographic conditions (typically every two hours when operating in more dynamic areas). Reson sound speed values are constantly compared against secondarily derived sound speed values from the ship’s onboard thermosalinograph flow-through system as a quality assurance measure. Roll, pitch, and heave motion corrections are applied in real-time via a POS MV 320 version 5 or a Seapath-380, using Marine Star DGPS correctors. The motion and positioning unit used will be noted in the processing logs. No tidal corrections are applied to the raw or processed data. Multibeam data quality is monitored in real-time by acquisition watchstanders. Ship speed is adjusted to maintain data quality and sounding density as necessary. Line spacing is planned to ensure one-quarter to one-third swath-width overlap between lines, depending on the environmental conditions and impact on the quality of the outer swath regions. Angles are generally left open (70°/70°) during transits to maximize data collection and are adjusted on both the port and starboard sides to ensure the best data quality and coverage. If outer beams are returning obviously spurious soundings (e.g., due to attenuation or low

The 2021 North Atlantic Stepping Stones: New England and Corner Rise Seamounts expedition (EX-21-04) was a combined mapping and remotely operated vehicle (ROV) expedition to the seamounts of the Northwest Atlantic that took place between June 30 and July 29, 2021. Operations during this 30-day at sea expedition included a combination of ROV dives in support of NOAA Ocean Exploration and its partner priorities as well as exploratory mapping operations targeting areas containing no or poor quality modern mapping data. The initial focus was on the U.S. Northeast Seamount and high seas areas, however, during the expedition weather altered the planned transect to outside Bermudan waters where three dives took place before rejoining the planned dive sites exploring a total of 19 seamounts and one canyon (Hydrographer) for water column exploration. During the expedition, 20 Deep Discoverer ROV dives were conducted from 300 m to 4187 m water depth for a total of 154 hours of bottom time, and surveyed using EM 304 multibeam sonar 54,710 square km over 30 days at sea. All data associated with this expedition have been archived and are publicly available through the NOAA Archives.

From July 14 - July 25, 2023 (Kodiak, Alaska to Unalaska, Alaska), NOAA Ocean Exploration completed the Seascape Alaska 3: Aleutians Remotely Operated Vehicle Exploration and Mapping expedition (EX2304), a combined mapping and remotely operated vehicle (ROV) expedition exploring the deep waters around the Aleutian Islands. Operations during this 12-day expedition included the completion of eight ROV exploration dives, including six full dives and two dives that were abandoned during descent due to various circumstances. ROV dives were conducted in water depths ranging from 780 m to 2800 m for a total of nearly 27 hours of bottom time (not including mid-water transects), focusing on exploring benthic habitats (including seep communities), geohazards, and water column communities. EX2304 also collected over 15,000 square kilometers of seafloor bathymetry and associated water column data using an EM 304 multibeam sonar. 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.

During EX2402, acoustic data were collected with the ship's EM 304 multibeam data (26 kHz), Knudsen 3260 sub-bottom profiler (3.5 kHz), the suite of five EK60/80 split-beam sonars (18, 38, 70, 120, and 200 kHz), and two ADCPs (38 and 300 kHz). More information about equipment used and methods employed can be found in the annual readiness report.

From October 16-November 3, 2022 (San Diego, California to Newport, Oregon), NOAA Ocean Exploration conducted mapping operations off the coast of California and Oregon in U.S. waters, aiding in closing bathymetric gaps within this region. Expedition EX-22-08 collected 32,416 square kilometers of bathymetry and associated water column data, 22,313 square kilometers of which were within the U.S. Exclusive Economic Zone and Territorial Sea deeper than 200 m, while 10,104 square kilometers were collected in international waters. 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 detailed sub-bottom survey targeted previously-identified sponge reefs in the Channel Islands National Marine Sanctuary. The exploratory mapping operations conducted during this cruise will provide initial characterization of the region, as well as data to support further exploration.

From August 6 - September 2, 2022 (Horta, Faial, Azores to San Juan, Puerto Rico) NOAA Ocean Exploration completed the Voyage to the Ridge 3 expedition (EX-22-06), a combined mapping and remotely operated vehicle (ROV) expedition to the Mid-Atlantic Ridge and Azores Plateau, Mid-Atlantic Ridge, and U.S. waters in the vicinity of Puerto Rico and the U.S. Virgin Islands. Operations during this 28-day expedition included the completion of 9 successful ROV exploration dives in the vicinity of the Azores, the Mid-Atlantic Ridge south of the Azores, and Puerto Rico. ROV dives were conducted in water depths ranging from 250 m to 6000 m for a total of 41 hours of bottom time. EX-22-06 also collected 56,769 square kilometers of seafloor bathymetry and associated water column data using an EM304 multibeam sonar. All data associated with this expedition have been archived and are publicly available through the NOAA Archives.

From September 5 - September 28, 2021, NOAA Ocean Exploration conducted mapping operations on the Blake Plateau within U.S. waters, aiding in closing the gaps within this region. The second of two cruises focused on mapping this region, EX-21-06 collected 25,800 square kilometers of bathymetry and associated water column data, 25,790 square kilometers of which were within the U.S. Exclusive Economic Zone and Territorial Sea deeper than 200 m. The exploratory mapping operations conducted during this cruise will provide initial characterization of the region, as well as data to support further exploration with remotely operated vehicles planned for EX-21-07.