Meg Stewart: What Does the Seafloor Look Like? Hydrography Can Tell Us, July 11, 2019


NOAA Teacher at Sea

Meg Stewart

Aboard NOAA Ship Fairweather

July 8 – 19, 2019


Mission: Cape Newenham Hydrographic Survey

Geographic Area of Cruise: Bering Sea and Bristol Bay, Alaska

Date: July 11, 2019

Weather Data from the Bridge
Latitude: 58° 36.7 N
Longitude: 162° 02.5 W
Wind: 1 knot N
Barometer: 1011.0 mb
Visibility: 10 nautical miles
Temperature: 58° F or 14° C
Weather: Partly cloudy, no precipitation

Red Sky
“Red sky at night, sailors’ delight. Red sky in morning, sailors take warning.” This old mariner’s adage did NOT prove to be true when I saw this sunrise viewed from NOAA Ship Fairweather at 5:21am yesterday. It turned out to be a perfect delight for a surveying day!


What is NOAA and the Teacher at Sea program?

You may be wondering what, exactly, am I doing going “to sea” with NOAA. First off, NOAA stands for the National Oceanic and Atmospheric Administration and originates back to 1807 with Thomas Jefferson founding the U.S. Coast and Geodetic Survey (as the Survey of the Coast) with a mission to provide nautical charts to the maritime community for safe passage into American ports. Over time, the Weather Bureau was added and then the U.S. Commission of Fish and Fisheries was developed. In 1970, these three agencies were combined under one umbrella organization and named NOAA, an agency that supports accuracy and precision of physical and atmospheric sciences, protection of life and property, and stewardship of natural resources. NOAA is within the Department of Commerce.

Meg on flying bridge
I am standing on the flying bridge of the Fairweather where you get a fantastic 360° view.

NOAA’s Teacher at Sea (TAS) program has existed since 1990, sending over 800 teachers on NOAA research cruises. The TAS mission is “to give teachers a clearer insight into our ocean planet, a greater understanding of maritime work and studies, and to increase their level of environmental literacy by fostering an interdisciplinary research experience.”  There is usually just one teacher sent per leg of a mission, that way the TAS gets full exposure to the research process and attention from the crew, scientists and staff on the ship. And it is true, everyone onboard has been friendly, helpful, welcoming, and willing to answer any question I might have, like, where is C deck? (That’s where my stateroom is located).


Science and Technology Log

Now that you understand NOAA’s mission, it should not surprise you that I am on a research cruise that is mapping a part of the seafloor that has not had detailed soundings. “Soundings” means the action or process of measuring the depth of the sea or other body of water. See the map below as that is where I am right now, in Bristol Bay. By the way, NOAA nautical charts are available for free at this NOAA site.

Bristol Bay nautical chart
The NOAA nautical chart of Bristol Bay, Cape Newenham and Hagemeister Strait. Note that where there are small numbers in the white and blue sections of the chart (that is all water), you can see the sounding depths to surface shown in fathoms. The red polygon is drawn on by me. We are working in the upper, northwest part of that “poorly mapped” section. Notice that there are essentially no soundings in that region.

When I’ve told friends, family and students that I was chosen to be on a NOAA research vessel that was compiling a detailed map of the sea floor off of Alaska, it was met with great surprise. “The ocean floor hasn’t been mapped before? How could that be?” In fact, more than 80 percent of the ocean bottom has not been mapped using modern, highly precise technologies.  But we do have a very coarse ocean floor – or bathymetric – map, created in the early 1950s by Marie Tharp using sounding data collected by the U.S. military and her collaborator Bruce Heezen. Tharp’s early map of the sea floor beautifully revealed the Mid-Atlantic Ridge and added another piece of evidence in support of the theories of continental drift plate tectonics. There’s a terrific Cosmos: A Spacetime Odyssey episode featuring Tharp.

1977 colorized ocean floor map
This is the Tharp and Heezen (1977) colorized ocean floor map. This map is used under the Creative Commons license.

Why we need a more detailed bathymetry map than the one created by Tharp and Heezen can be explained by the original mission of the early version of NOAA. Jefferson wanted to build a “…survey to be taken of the coasts of the United States…” in order to provide safe passage of ships to ports within the navigable waters of the U.S. As the Bristol Bay chart above shows, there are still coastal areas that have limited to no data. Without detailed charts, mariners cannot know where the shallower waters are (called shoals), or rock obstructions, shifted underwater sand bars, shipwrecks, or other hindrances that cause safety concerns to the movement of boats.

The hydrographic Survey Team on the NOAA Ship Fairweather use several 30 foot boats, called launches, with a multibeam echosounder attached to the hull (the bottom of the ship). The multibeam echosounder uses sonar and is a device useful for both shallow and deep water. In a nutshell, depth measurements are collected by calculating the time it takes for each of the sound pulses to travel from the echosounder through the sea water to the ocean floor and back again. The distance from the instrument to the seafloor is calculated by multiplying the travel time by the speed of sound through seawater, which is about 1,500 meters/second or 4,921 feet/second. Right before a hydrographic survey is started, the team collects information on the conductivity, temperature and depth of the sea water, as temperature and salinity will modify the density and change the travel time of the sonar pulses. The video below can explain the process further.

This NOAA video explains multibeam sounding and hydrographic operations.
launch with echosounder
A launch on a lift right before going out to survey. The multibeam echosounder is permanently fixed to the bottom of the hull. It’s a square, rigid box that sits flat against the hull in front of the keel.
Ali in a launch
This is Ali Johnson in the cabin of a launch. She is a hydrographic survey technician and is analyzing the multibeam echosounder data as it is being collected. The length of a launch is 32 feet, and all the technology needed for the hydrographic surveys are directly on boats in the cabin. Post-processing, or stitching the completed surveys into one comprehensive product, is done “back in the office” on Ship Fairweather.

The software used to collect the soundings is created by the multibeam echosounder manufacturer, so the collection of millions of points on a transect is seamless. Data collection runs are taken over multiple days and several “legs” or extended periods of time when the crew are all out at the same time on the Fairweather.  Following collection transects, the data are then post-processed using Caris HIPS and SIPS, which is the software that the Fairweather hydrographers use for data processing.

screen showing bathymetry
A close-up of one of the monitors that shows what the sounding data look like. By looking at these data returns, the hydrographers can tell immediately if something is not right with the equipment. The two windows that show maps colored red to yellow to blue (top right and bottom left) show the bathymetry. The red areas are shallow depths and the blue are deeper depths, relatively speaking. Also notice the window at the bottom right with a triangle and circle within the triangle; that is showing the fan-shape of the echosoundings.


Personal Log

We’ve motored to a new location, Cape Newenham, which is the name of this mission, so we will be here for about a week. When we got underway, the ship got to really rocking and my stomach could not handle it. I had one bad night but I am now fine and ship shape!

Cape Newenham is at latitude 58°N so we are up close to the Arctic Circle (66.5°N). At this time of year, there are about 5 hours of darkness per night here in Alaska, which is really cool. Compare that what we have in New York…

Anchorage v NYC
For July 11, 2019, the number of daylight hours in Anchorage, AK (closest large city to where I am now) is 18 hours and 41 minutes. Times of sunrise and sunset are also given….the sun sets at 11:25pm today! And in NYC, NY (where my school is located), you are getting four fewer daylight hours, or about 15 hours of light. Again, times of sunrise and sunset are shown. Source for both: https://www.timeanddate.com/sun/usa
Launches and Fairweather
Launches waiting to get underway. All boats going out for surveys stay close to the Fairweather until everyone is securely in their boat, just in case of MOB (man overboard).
Fairweather anchored
This is where Ship Fairweather is anchored for the next few days, as the survey crews transect the project area. We are on the southern side of Cape Newenham. Again, the terrain is tree-less, though we are now adjacent the mainland of Alaska. I’ve seen so many types of sea birds, but the puffins are the best because they seem to not have figured out how to fly. I hear there are walrus in the area, but I haven’t spotted one as yet.


Did You Know?

You probably know that Charles Darwin was the naturalist on board the HMS Beagle which set sail on December 27,1831. Over the nearly five years the Beagle was at sea, Darwin developed his ideas on natural selection and evolution of species. But what you might not know is that the captain of the Beagle, Robert FitzRoy, was an officer in the Royal Navy, a meteorologist and hydrographer. In fact, the primary mission of the Beagle was to survey the coastline of South America and, in particular, the Strait of Magellan, at the southernmost tip. Better, more accurate charts were needed by the British government, to navigate the treacherous, rough waters of the channels. In addition, FitzRoy was a protégé of Francis Beaufort (who developed the Wind Force Scale which is still used to help explain wind speed) and both worked together to create the science of weather forecasting.


Quote of the Day

“In every outthrust headland, in every curving beach, in every grain of sand there is the story of the earth.” – Rachel Carson

4 responses to “Meg Stewart: What Does the Seafloor Look Like? Hydrography Can Tell Us, July 11, 2019

  1. Meg, You are such a good writer! I could actually follow your descriptions of the complex equipment NOAA is using. Question: Do animals get affected by the echosounder? I am so envious and excited for you. Also, is it hard to go to sleep or sleep in?

    • Good question(s), Miriam! And both I had prior to coming out on the ship. I asked the XO (executive officer) and the chief hydrographer whether the echosounder impacts fish and mammals in any way. The answer was that, given the frequencies of the echosounder used on the launches, they see no impact. They said that they’ve seen whales and dolphins come alongside the boats and continue to swim side-by-side. The thought is that the noise from the ships themselves, the engines and propellers, multiplied by the number of ships on the water, is more problematic for animals than the sounding devices for hydrography. Also, the NOAA boats and ships definitely avoid known habitats (we bypassed a right whale habitat off of the Aleutians) and log all sea mammal sightings.

      Your other question, how is the sleeping? It’s great! My room is below the water line, so I can’t see out of a port hole and I feel I’m a little closer to the engines, so it’s loud in my berth. I put my head on the pillow and I’m out in less than a minute. The rocking is a great way to sleep and the noise is just white noise. I wake up early because I’m naturally an early riser.

      Thanks for writing, Miriam!

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