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

Denise Harrington: The Best Day Ever, April 30, 2014

NOAA Teacher at Sea
Denise Harrington
Aboard NOAA Ship Rainier
April 20 – May 3, 2014

Mission: Hydrographic Survey

Geographical Area of Cruise: North Coast Kodiak Island

Date:  April 30, 2014, 11:44 a.m.

Location: 58 03.175’ N  127o 153.27.44’ W

Weather from the Bridge: 6.3C (dry bulb), Wind 5 knots @ 250o, clear, 1-2′ swell.

Our current location and weather can also be seen at NOAA Shiptracker: http://shiptracker.noaa.gov/Home/Map

Science and Technology Log

The last couple of days have been the best ever: beautiful weather, hard work, deep science. We acquired data along the continental shelf and found a cool sea floor canyon and then set benchmarks and tidal gauges.

In hydrography, we gather data in seven steps, by determining: our position on Earth, depth of water, sound speed, tides, attitude (what the boat is doing), imagery and features.  Step 1 is to determine where we are.

In this picture you can see a GOES satellite antenna and a GPS antenna that helps us determine our precise location.

In this picture you can see a GOES satellite antenna (square white one) that is used to transmit tide data ashore and a GPS antenna (the small white eggs shaped one) that provides the tide gauge with both position and UTC time. Photo by Barry Jackson

In this picture  Brandy Geiger, Senior Survey Technician, uses the GOES from various locations to determine the exact location of the tide gauge.

In this picture Brandy Geiger, Senior Survey Technician, uses GPS to record the positions of the benchmarks we have just set for the tide gauge. Photo by Barry Jackson

tide gauge install 023

Where we are happens to be the most beautiful place on earth. Photo by Barry Jackson

 

In Step 2, we determine the depth of the water below us.

Bathymetry is a cool word that means the study of how deep the water is.  Think “bath” water and metry “measure.”  When your mom tells you to get out of the tub, tell her to wait because you’re doing bathymetry.

As I explained in my first blog, we measure depth by sending out a swath of sound, or “pings,” and count how long it takes for the pings to return to the sonar, which sits beneath the ship or smaller boat.

Yesterday we used the multi-beam sonar to scan the sea floor.  Here is a screen shot of the data we collected.  It looks like a deep canyon, because it is!

Here is the image of the trench Starla Robinson, a Senior Survey Technician, and I discovered.  We decided it should be named Denla Canyon, after us.

Here is the image of the sea floor canyon Starla Robinson, a Senior Survey Technician, and I discovered. We decided it should be named Denla Canyon, after the two scientists who discovered it.

Here I am, gathering pings.

Here I am talking with "the bridge,"  the team responsible for navigating the ship while surveyors collect data.

While collecting data, I kept in contact with “the bridge,” the team responsible for navigating the ship, by radio to ensure the ship’s safety and maximum, quality data acquisition.     Photo by Starla Robinson

 

Step 3, we take into consideration the tide’s effect on the depth of the water.  Tides are one predictable influence on water depth. There are over 38 factors or “constituents” that influence the tides.  The gravitational pull of the sun and the moon at various times of the day, the tilt of the earth, the topography, and many other factors cause water to predictably bulge in different places on earth at different times. The Rainier crew works 24 hours a day and 7 days a week, so they must find a way to measure depth throughout the days and month, by taking into account the tide. Arthur Doodson, who was profoundly deaf, invented the Doodson Numbers a system taking into account the factors influencing tide in 1921. Flash forward to the 21st century, our Commanding Officer, Commander Rick Brennan worked with a team of NOAA scientists to develop a software program called TCARI, as an alternate method to do tide adjustments, taking into account 38 factors, even the moon’s wobble. Inventions abound at NOAA.

The Rainier crew worked for 14 hours today to set up a tide gauge station, an in depth study of how the tide affects our survey area.  On this map, there is a Red X for each tide gauge we will install.  This process only happens at the beginning of the season, and I feel fortunate to have been here–the work we did was….amazing.

 

Each Red X is approximately where a tide gauge will be installed.  The one we installed today in Diver's Bay is in the north west corner of the sheet map.

Each Red X is approximately where a tide gauge will be installed. The one we installed today in Driver Bay is in the north west corner of the sheet map.

You can see an animation here that shows the combined effect of two sine waves that produce a signal like our tide data.  Just imagine what it looks like when you factor in 38 different variables.

The earth goes around the sun in 24 hours and moon goes around the earth in a little more than 12 hours, much like these two gray sine waves. Interestingly, when you add two different waves, you get the wonky blue sine wave, with ups and downs. This combined effect of the sun and the moon (two dots) causes the ups and downs of the tide (blue wave). Graph taken from Russell, D. Acoustics and Vibration Animation, PSU, http://www.acs.psu.edu/drussell/demos/superposition/superposition.html.

 

Low tide is the best time to see sea stars, mussels and barnacles, but it is also a more hazardous time in the tidal cycle for mariners to travel. Therefore, navigational charts use the mean lower low water level, low tide, for the soundings, or depth measurements on a chart.  The black numbers seen on a nautical chart, or soundings, represent depth measurements relative to mean lower low tide. Driver Bay, the area on the chart where we installed the tide gauge today, is the crescent shaped bay at the northwest end of Raspberry Island.

This is a nautical chart used to help mariners navigate safely.

This is a nautical chart used to help mariners navigate safely.

Installing Tide Gauge Stations

Before gathering sonar data, ground and boat crews install a tide gauge to measure changes in water level and to determine the mean lower low water level datum. A tide gauge is a neat device that has air pumped into it, and uses air pressure, to determine how deep the water is.   The tide gauge uses a formula of (density of sea water)(gravity)(height) = pressure.  The gauge measures pressure, and we apply factors for gravity and sea water.  The only missing factor is height, which is what we learn as the gauge collects data.  This formula and nuances for particular locations is a fascinating topic for a blog or master’s thesis.  Scientists are looking for tidal fluctuations and other location specific variances. Then, by computer they determine the mean lower low tide depth, factoring in the tidal fluctuations.

There are permanent tide gauge stations all over the world.  The nearest permanent tide gauge station to our study area is in Kodiak and Seldovia.  These permanent gauges take into account many factors that affect tides over a 19 year period of time, not just the gravitational pull of the moon.

The tide gauge stays in place for at least 28 days (one full tidal cycle).  During the month, data of the tides is collected and can be compared to the other tide gauges we install.

Installing the Tide Gauges and Benchmarks

Excitement built as the crew prepared for the “Tide Party,” packing suitcases full of gear and readying the launches.  Installing Tide Gauges signals the beginning of the season and is one of the few times crew gets paid to go on shore.

 

Why Bench Mark?

There are three reasons I have figured out after many discussions with patient NOAA crew as to why we put in bench marks.

 

I installed this benchmark by having a hole drilled in bedrock and affixing the benchmark with concrete if anyone ever returns and needs to know their exact location.

I installed this benchmark in Driver Cove by having a hole drilled in bedrock and affixing the benchmark with concrete if anyone ever returns and needs to know their exact location. Photo by Barry Jackson

The first reason we install benchmarks is to provide a reference framework to ensure both our tide staff and the tide gauge orifice are stable and not moving relative to land.  The second reason is if we ever come back here again to gather or compare data to previous years, we will know the elevation of the tidal datum at this location relative to these benchmarks and can easily install a new tide gauge.  The third reason is that the earth and ocean floor changes constantly.  As scientists, we need to make sure the survey area is “geologically stable.”  We acquire several hours of GPS measurements on the primary benchmark to measure both its horizontal and vertical position relative to the earth’s  reference frame.  Should there ever be an earthquake here, we can come back afterwards and measure that benchmark again and see how much the position of the Earth’s crust has changed.  After the last big earthquake in Alaska, benchmarks were found to move in excess of a meter in some locations!

Teacher on Land Polishing Her Benchmark Photo by Brandy Geiger

Teacher on Land
Polishing Her Benchmark
Photo by Brandy Geiger

Installing the Benchmark

Today, our beach party broke into two groups.  We located stable places, at about 200 foot intervals along the coastline.  We drilled 5 holes on land and filled them with concrete.  A benchmark is a permanent marker you may have seen at landmarks such as a mountain peak or jetty that will remain in place for 100 years or more.  We stamped the benchmark by hand with a hammer and letter stamps with our station identification.   If we chose a good stable spot, the benchmark should remain in the same location as it is now.

Tide Gauge

As one group sets up benchmarks, another group installed the tide gauge.

 

Here, Chief Jim Jacobson, Lead Survey Technician, sets up a staff, or meter stick, I used to measure the change in water depth and others used for leveling.

Here, Chief Jim Jacobson, Lead Survey Technician, sets up a staff, or meter stick, I used to measure the change in water depth and others used for leveling.  Photo by Barry Jackson

To install the tide gauge, you must have at least three approved divers who install the sensor in deep water so that it is always covered by water.  Because there were only two crew on board trained to dive, Lieutenant Bart Buesseler, who is a dive master, was called in to assist the team.   The dive team secured a sensor below the water.  The sensor measures the water depth with an air pressure valve for at least 28 days.  During this time there is a pump on shore that keeps the tube to the orifice pressurized and a pressure sensor in the gauge that records the pressure. The pressure is equal to the number of feet of sea water vertically above the gauge’s orifice. An on-board data logger records this data and will transmit the data to shore through a satellite antenna.

Divers install the tide gauge, and spent most of the day in the cold Alaska waters.  Good thing they were wearing dive suits!  Photo by Barry Jackson

Divers install the tide gauge, and spent most of the day in the cold Alaska waters. Good thing they were wearing dive suits! Photo by Barry Jackson

Leveling Run

After the gauge and benchmarks are in place, a group does a leveling run to measure the benchmark’s height relative to the staff or meter stick.  One person reads the height difference between 5 different benchmarks and the gauge. Then they go back and measure the height difference a second time to “close” the deal.  They will do the same measurements again at the end of the survey in the fall to make sure the survey area has not changed geographically more than ½ a millimeter in height!  Putting the bubble in the middle of the circle and holding it steady, leveling, was a highlight of my day.

Observation

Finally, a person–me– watches the staff (big meter stick above the sensor) and takes measurements of the water level with their eyes every six minutes for three hours.  Meanwhile, the sensor, secured at the orifice to the ocean floor by divers, is also measuring the water level by pressure. The difference between these two numbers is used to determine how far below the water’s surface the orifice has been installed and to relate that distance to the benchmarks we have just leveled to.  If the numbers are consistent, then we know we have reliable measurements.  I won’t find out if they match until tomorrow, but hope they do.  If they don’t match, I’ll have to go back to Driver Bay and try again.

As we finished up the observations, we had a very exciting sunset exit from Raspberry Island.  I was sad to leave such a beautiful place, but glad to have the memories.

Last minute update: word just came back from my supervisor, Ensign J.C. Clark, that my tidal data matches the gauge’s tidal data, which he says is “proof of my awesomeness.” Anyone who can swim with a car battery in tow is pretty awesome in my book too.

The data Starla Robinson and I collected is represented by the red line and the data the gauge collected is represented by the blue line.  The exact measurements we collected are on the table.

The data Starla Robinson and I collected is represented by the red line and the data the gauge collected is represented by the blue line. The exact measurements we collected are on the table.

Spotlight on a Scientist

Lieutenant Bart Buesseler came to us straight from his family home in the Netherlands, and before that from his research vessel, Bay Hydro II.  The main reason our CO asked him to leave his crew in Chesapeake Bay, Maryland, and join us on the Rainier is because he is a dive master, capable of installing our sensors under water, and gifted at training junior officers.

 

Lieutenant Beusseler knows he needs to be particularly nice to  Floyd Pounds, an amazing cook from the south who cooks food from every corner of our ocean planet.

Lieutenant Beusseler knows he needs to be particularly nice to the amazing chefs aboard Rainier, including Floyd Pounds, who cooks food from every corner of our ocean planet with a hint of a southern accent.

During his few years of service, LTJG Buesseler adventured through the Panama Canal, along both coasts of North America, and has done everything from repairing gear to navigating the largest and smallest of NOAA vessels through very narrow straits.  He loves the variety: “if I get tired of one task, I rotate on to another to keep engaged and keep my mind sharp.”  He explains that on a ship, each person is trained to do most tasks.  For example, he says, “during our fast rescue boat training today, Cal led several rotations. But what if he is gone? Everyone needs to be ready to help in a rescue.”  Bart says at NOAA people educate each other, regardless of their assignments, “cultivating information” among themselves. Everyone is skilled at everything aboard Rainier.
In the end, he says that all the things the crew does are with an end goal of making a chart.   His motto? Do what you love to do and that is what he’s doing.

Personal Log

Today was a special day for me for many reasons.  It is majestic here: the stark Alaskan peninsula white against the changing color of the sky, Raspberry Island with its brown, golden, crimson and forest green vegetation, waterfalls and rocky outcroppings.  I’m seeing whales, Puffins, Harlequin Ducks and got up close with the biggest red fox ever.  Most importantly, I felt useful and simultaneously centered myself by doing tide observations, leveling and hiking.  I almost dove through the surf to make it “home” to the ship just in time for a hot shower. Lieutenant Buesseler’s reference to “cultivating information” rings very true to me.  In writing these blogs, there is virtually nothing I came up with independently.  All that I have written is a product of the patient instruction of Rainier crew, especially Commander Brennan. Each day I feel more like I am a member of the NOAA crew here in Alaska.