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Elli Simonen: Data, Calibrating Data and Surveying, July 15, 2023

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

Weather Data

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. 

photo of two adjacent computer monitors with different views of the collected survey data imposed on charts or maps

Survey Data shown as green strips.

a small boat (a survey launch) mounted on the port side of NOAA Ship Fairweather, as seen from the deck in front of another mounted launch (only partially visible). Beyond the side of the ship, the still water of a bay extends toward the steep green hill that lines the far side. Another launch, already deployed, is visible on the water at a distance.

Survey launches being stored on NOAA Ship Fairweather as well as one deployed in the harbor

Elli stands on the deck of a small boat. She's wearing a life vest and her Teacher at Sea hat. We have a partial view of the launch's wheelhouse to her left and an electronic winch to the right. Behind Elli the waters are calm, and we can see mountains in the distance.

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.

view of two computer monitors, two keyboards, and two computer mice on a desk

Planning the Patch Test

photo of a computer screen; it is difficult to see what is being displayed, but Elli has circled one area and added the label "shipwreck"

Map of the planned surveys for the Patch Test.

photo of a computer screen displaying bathymetric data. much of the area appears flat (colored teal blue) but there is a small, raised, orange portion in the shape of a ship lying on its side

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.

a conductivity, temperature, an depth probe stored in front of a computer tower inside the survey launch's wheelhouse. the probe looks like a white cylinder strapped inside a metal frame that tapers at the top

CTD on the survey launches.

three crewmembers, wearing orange life vests and white hard hats, stand around a piece of equipment mounted at the corner of the aft deck of NOAA Ship Fairweather. a computer is mounted in a blue frame; above extends a blue boom and pulley. a coil of rope hangs on the side. Beyond the ship, the waters are gray with some caps, distant mountain ranges appear in shades of dark blue, and a cloudy, gray-white sky tops the picture.

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.

two people look at a computer screen in the computer lab. The survey tech, seated at the computer station, points toward multicolored swaths against a black background on the right monitor. Elli stands be hind him to view over his shoulder. On the desk are messy folders and papers, a small potted plant, and an action figure.

Survey Technician showing TAS Elli Simonen the process of cleaning survey data

Personal Log

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.

a view of Elli's stateroom. To the left is a metal warddrobe and a metal sink. To the right is a filing cabinet, a simple bed, and the edge of a metal chest of drawers. There's an open porthole along the back wall, and light shines through it onto the wall, forming a bright circle above the bed.

This is TAS Elli’s room aboard NOAA Ship Fairweather at 9:45pm

view through a sea-sprayed porthole of water and mountains. the sun is low in the sky.

View out my window in the Gulf of Alaska.

Did you know?

screenshot of a political map of the continents of the world, with North America at the center. Neon green lines color the North American coastline and extend in webs throughout the rest of the ocean. the map is titled "Data Centre for Digital Bathymetry Viewer."

This map shows, in green, the areas of the world that have bathymetry data, from NCEI, https://www.ncei.noaa.gov/maps/iho_dcdb/

Animals Seen

an otter floats on its back in the water.

Otter swimming near NOAA Ship Fairweather

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