Emina Mesanovic, Acoustic Lab: Let’s Make Some Maps, July 28, 2014

NOAA Teacher at Sea

Emina Mesanovic

Aboard the NOAA Ship Pisces

July 20 – August 2, 2014

 Mission: Southeast Fishery- Independent Survey

Geographic area of the cruise: Atlantic Ocean, off the coast of North Carolina and South Carolina

Date: July 28, 2014

Weather Information from the Bridge

Air Temperature: 27.5 C

Relative Humidity: 86%

Wind Speed: 15.03 knots

 Science and Technology Log

There is a lot of work that goes into allowing the fishery team to be able to set traps every day. The acoustics lab/ night shift is responsible for creating the maps of the seafloor that will be used the following day. The team consists of David Berrane a NOAA fisheries biologist, Erik Ebert a NOAA research technician, Dawn Glasgow from the South Carolina Department of Natural Resources and a Ph.D student at the University of South Carolina, as well as Mary a college student studying Geology at the College of Charleston and Chrissy a masters student at the University of South Carolina. This team is amazing! Starting at around 5:00 pm the day before they stay up all night mapping the ocean floor.

The night shift working together
The night shift collecting data

Every night Zeb Schobernd lets the night shift know which boxes they will work on. These boxes are created in the offseason by the research scientists, they base their selection on information from fishermen, the proximity to already mapped areas, weather and previous experiences. The first step in creating a bathymetric map is to create a line plan, which lets the ship know which area will be covered. The average line takes about half an hour to complete but they can take up to several hours. The ship drives along these lines all night long while the team uses the information that is gathered to create their maps.

So how do they get this information? The ship uses sonar to collect data on the water column and the ocean floor. The Pisces has a 26 multi-beams sonar system, which allows the research team to create a better picture, compared to using single beam sonar. The beams width is about 3 times the depth of water column. This means that depending on how deep the water is in any given location, it will determine how many lines need to be run to cover the area.

Multibeam sonar
Multi-beam sonar (picture from NOAA)

The picture below is one of the computer screens that the scientists look at throughout the night. It provides the sonar information that will then be used to map the floor. Sonar works by putting a known amount of sound into the water and measuring the intensity of the return. A rock bottom will yield a stronger return while a sand bottom will absorb the sound and yield a less intense return. In the image red means that there is a more intense return while blue and yellow signifies a less intense return. You will notice in the center screen there is a strong red return at the top of the beam this is because the ship is sending out the sound and it takes about four meters until you start recording information from the sea floor.

SIMRAD70 (multi-beam sonar)
SIMRAD (multi-beam sonar)

Finally before the maps can be created the team has to launch an XBT (expendable bathy thermograph) two times per box or every four hours. The XBT measures the temperature and conductivity of the water, this is important because sound travels at different rates in cold versus warm water. This information is then used when the scientists calculate the sound velocity, which is used to estimate the absorption coefficient of sound traveling through the water column.

 

Once the data is collected the team begins the editing process. First they have to remove random erroneous soundings in order to get an accurate map; they fondly call this process dot killing (this basically means getting rid of outliers). They do this by drawing a box around the points of data they want to remove and deleting the point. Next they apply tide data to account for the deviations in the tides, this information is obtained from NOAA and is based on the predicted tides for the area. Finally they apply the sound absorption coefficient.

Editing the data (killing dots)
Editing the data (killing dots)

The final product is put into GIS (Geographic Information Systems), which the chief scientists will use to determine where the traps should be set the following morning. On the map below blue indicates the deepest areas while red shows the shallowest. The scientists want to place the traps in areas where there is a large change in depths because this is usually where you will find hard bottoms and good fish habitats.

Finished map (red shallow, blue deep)
Finished map

Personal Log

I have spent the past three nights in the Acoustics/Computer Lab with the night shift mapping the ocean floor. While the ship sails along the plotted course, I have had the opportunity to see the sunrise and sunset on the Pisces as well as a lightning storm from the top deck.

images
Lighting on the ocean (picture from sciencedaily)

On Thursday night a little after midnight after launching the XBT we see decided to go onto the top deck of the Pisces to get a better look at the lighting storm in the distance. Even at night it was still humid and hot and as we climbed up to the top deck it was dark all around us until suddenly there would be a flash of color in the clouds and you could see everything, until it went dark again. We tried to take a picture but the lightening was just too fast for our cameras. This is the closest picture I could find to what it was like that night except the water was not calm.

 

SPOTLIGHT ON SCIENCE

Name: Erik Ebert                  Title: Research Technician

Erik editing data collected on Sunday July 26th.
Erik editing data collected on Sunday July 26th.

Education: Cape Fear Tech (Wilmington, NC)

How long have you worked for NOAA/NOS: 6th field season, 5th year

Job Summary: I work on ecosystem assessments throughout the Gulf of Mexico South Atlantic & Caribbean

– Team oriented production of ocean floor maps

– System setup & keeping the acoustic systems operating correctly

How long have you participated in this survey: Since 2010

What do you like about your job: That the data we collect, and the maps we create can be used again for different studies. The types of data we collect includes bathymetric data, information on the water column, & fish that populate the water column.

How many days are you at sea: 60 days (April-November)

What do you do when you are not on the boat: Process & produce fish density maps from the data collected during the cruises. I also work for National Ocean Services (provide data to policy & decision makers to the state of the ecosystem)

Most challenging about research on a ship: Being away from home is the biggest challenge.

What would be your ideal research cruise: My ideal research cruise would be a cruise similar to what we just completed in Flower Garden Banks in the Gulf of Mexico. It was a 3-year assessment of the reef ecosystem using ROV, Diving and Acoustics to study how the ecosystem changed over time.

Favorite fish: Trigger Fish “cool swimming behavior”

More information about See Floor Mapping   http://www.noaa.gov/features/monitoring_1008/seafloormapping.html

COOL CATCH

Crab with three sea anemones attached to its shell
Crab with three sea anemones attached to its shell

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