By Lt. j.g. Michelle Levano
As NOAA Ship Rainier underwent repairs in South Seattle, the ship’s survey launches and their crews carried out a project to update nautical charts around the Port of Everett and its approaches in Possession Sound. The boats used state-of-the-art positioning and multibeam echo sounder systems to achieve full bottom coverage of the seafloor.
The ports of Seattle, Tacoma, and Everett have experienced an increase in vessel traffic and capacity within the last decade. The Port of Everett serves as an international shipping port bringing jobs, trade, and recreational opportunities to the city. Across Possession Sound, Naval Station Everett is the homeport for five guided-missile destroyers, and two U.S. Coast Guard cutters. The data collected from this project will support additional military traffic transiting to and from Naval Base Kitsap in addition to the Washington State Ferries’ Mukilteo/Clinton ferry route, commercial and tribal fishing, and recreational boating in the area.
Some areas of the charts outside of Everett are based on data acquired between 1940 and the 1960s, a time when sonar technology did not allow acquisition of full bottom coverage. Complete multibeam coverage will provide mariners with modern, highly accurate information on shoals, rocks, and intertidal mudflat locations. During the first week of May, a team of nine Rainier crew members moved four survey launches from Lake Washington, where Rainier was docked, to Everett. The team, consisting of wardroom, survey, and deck department members, conducted 17 days of survey.
During this project, Rainier trained several individuals to become qualified hydrographers in charge and/or launch coxswains. Much of the multibeam acquisition in the Everett project was more gradual and shallow compared to the “steep and deep” coastline of Alaska that Rainier is more accustomed to seeing. This served as a perfect place for individuals to increase confidence and capability after a long winter repair period.
In addition to updating depth data, the Rainier survey team updated chart symbology information found on paper and electronic navigational charts of the area. Some examples of chart symbology include rocks, kelp beds, aids to navigation, traffic separation schemes, and other man-made and natural features. Traditionally, chart features are positioned using the ship’s 19-foot outboard skiffs. Equipped with a GPS positioning unit, the skiffs carefully approach a charted or new feature, and get as close as safely possible to determine the location and height. The Port of Everett contains many man-made shoreline features such as pilings, docks, and breakwater which are ideal for using a topographic laser to collect feature attribution.
For this project, the team used Rainier’s relatively new jet-propelled boat, RA-2, that is equipped with lidar. Using sixteen laser beams, light reflects off an object and is detected by a receiver; similar to how the sonar is used to find objects on the seafloor. Topographic laser feature attribution allows the surveyor to locate and place these features accurately with height information combined with precise positioning and orientation (roll, pitch, and yaw of the vessel) data.
The crew to gained experience and developed procedures using laser technology for feature positioning and height, which is safer for the crew than previous collection methods. Now, survey crews can collect highly accurate feature information from a distance. This experience, training, and procedure development was an important component of preparation for upcoming fieldwork in Alaska where the rocky and rugged Alaskan coastline experiences a large tidal range and contains many features that must be correctly identified and positioned. Rainier’s survey team received support on this project from NOAA’s Office of Coast Survey’s Hydrographic Systems and Technologies Branch, which provided additional training on lidar use and data processing.
Stay tuned for future Rainier survey updates as she heads north to survey Tracey Arm outside of Juneau, Alaska, and the ship’s adventures in California later this summer!
Rainier would like to thank the Port of Everett for accommodating the ship’s launches throughout the duration of this survey project.