NOAA Teacher at Sea
Elli Simonen (she/her)
Aboard NOAA Ship Fairweather
July 10, 2023 – July 28, 2023
Mission: Hydrographic Survey of the Pribilof Islands
Geographic Area of Cruise: Pribilof Islands, Alaska
Date: July 16, 2023
Location: 55’21.02° N, 161’02.02° W
Outside temperature: 11°C
Water temperature: 10°C
True Winds: 337°, 6.5 kts
Skies: Overcast and Cloudy
Science and Technology Log
What is Surveying?
I was in port with the NOAA Ship Fairweather for a little under a week but right now we are en route to the Pribilof Islands. During the time at port, the survey team surveyed surrounding areas, calibrated equipment and practiced troubleshooting survey systems. The goal of surveying is to gather the bathymetry data of the seafloor, or the depths and shape of the seafloor.
Surveying equipment is located on NOAA Ship Fairweather as well as four smaller boats called survey launches, which each get deployed from the ship. Depending on the mission, sea conditions and the project plan, the ship or launches may both be used, or a combination of both.
Global Positioning System (GPS) records position. The Inertial Measurement Units (IMU) measures the motion of the ship. Multibeam Echosounder (MBES) is when sound is pinged from a vessel to the seafloor and the time lapse is used to determine the depth of the seafloor. MBES is a type of sonar that uses multiple beams to get a more complete picture of the seafloor with depths and characteristics. After the data is pinpointed to a specific location, variability associated with tides is also taken into account by transforming the data vertically to the mean lowest low tide. Bathymetry data taken on NOAA Ship Fairweather as well as its four survey launches appears as strips on a map, as the ship or boat moves.
Data is measured to the mean lowest low tide because that level of water is on average the lowest of any tide for a given area. Using the lowest depth in navigation is conservative, thus allowing vessels to navigate safely through mapped waters.
Survey Data shown as green strips.
Survey launches being stored on NOAA Ship Fairweather as well as one deployed in the harbor
TAS Elli Simonen aboard one of the survey launches.
Calibrating the Data
During our time in port we took out some of the survey launches to perform a patch test; that is, calibration procedures to ensure the data we collect is as accurate as possible. A correctly calibrated system will show the same mapping of the seafloor in repeated tests, without the influence of confounding variables – speed, direction and ship motion. In a patch test, time delay, pitch, roll and heading are calculated multiple times over different depths, obstructions and slopes on the seafloor and compared to known data. The obstruction we surveyed was a shipwreck.
Planning the Patch Test
Map of the planned surveys for the Patch Test.
Survey Data showing the Wreck
To correct for how the speed of sound changes in ocean water, during surveying every four hours Conductivity, Temperature and Depth (CTD) is measured. The CTD measures Salinity and Pressure of the Water Column, aspects that can change the speed of sound. The CTD is used to further calibrate data because different depths have different levels of salinity and temperature, and therefore distort how fast the sound travels. CTD data is used in post-processing to correct for any distortions.
CTD on the survey launches.
Moving Vessel Profiler (MVP), a type of CTD that can be used while the ship is in motion, being deployed on NOAA Ship Fairweather by members of the surveying team.
Where does the data go?
Once the survey technicians gather bathymetry data, they still need to edit it before passing it along to National Centers for Environmental Information (NCEI), who package it for public view and is the data repository for environmental data in the U.S. and the U.S. Office of Coast Survey who create navigational charts. Editing the data involves rejecting spurious noise that MBES picked up that is out of range or incorrect. This data then is transformed into charts and more standardized bathymetry data.
Survey Technician showing TAS Elli Simonen the process of cleaning survey data
Members of the survey team are all smart, respectful and patient and take the time to explain to me the science at play no matter how many questions I have. I spend the majority of my day with the survey team but also explore other areas of the ship. I have now been onboard for over a week and things are beginning to feel routine. The sun does not set here until about 10:30pm and rises around 6am. Meals are served at regular times and more importantly, at least to me, coffee is available 24/7.
This is TAS Elli’s room aboard NOAA Ship Fairweather at 9:45pm
View out my window in the Gulf of Alaska.
Did you know?
- The USA offers their bathymetric data for free; Not all countries do this. (https://www.opencpn.org/OpenCPN/info/chartsource.html)
- 75% of the ocean floor has not been mapped
This map shows, in green, the areas of the world that have bathymetry data, from NCEI, https://www.ncei.noaa.gov/maps/iho_dcdb/
Otter swimming near NOAA Ship Fairweather