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Mapping the Sound

January 5, 2016

We're surrounded by oceans, but scientists know more about the topography of Mars than they do about the seafloor. The University of Washington's School of Oceanography wants to change that through high-tech sonar mapping equipment.

It's 5:00 a.m. and Katherine Ball has been up since midnight processing seafloor mapping data on an ocean research vessel. The data shows high-resolution images of Puget Sound’s seafloor and Katherine, a UW oceanography student, is tired but invigorated. “This area has some holes in NOAA’s mapping,” she says. “So this is very good for them and very good for us.”

Katherine is part of a three-day research cruise with staff and students from the University of Washington’s School of Oceanography. The goal? To map the seafloor.

Why is mapping the ocean floor a big deal? For starters, over 90 percent of the ocean floor has not been mapped in detail. Much of it is too dark and deep to map optically — for example, the Challenger Deep area beneath the western Pacific Ocean is over 36,000 feet deep.

The seafloor of the Puget Sound (Courtesy of Laura James).

In Washington State's Puget Sound, the average depth is only 450 feet, but some of it also remains unmapped. The mapping data the team gathers will be added to the National Oceanic and Atmospheric Administration, or NOAA, nautical charts. Detailed nautical charts are critical for safe ship navigation through Puget Sound, an area that encompasses a bustling urban inlet.

One of the areas targeted is the outer portions of the Elwha River delta, site of the nation’s largest dam removal project. Emily Roland, who is a geophysicist at UW and assisting on the cruise, wants to see if there are any changes in the seafloor as a result of the dam removal.

“What we’re hoping is that we can see some dramatic kind of morphology or shapes,” she says. “Features on the seafloor that are indicating large currents are ripping through in that portion of the Sound.”

So how does one map the seafloor? Through multibeam sonar technology.

“We’re literally putting sound through the water column, reflecting off the seafloor, back up to our remote sensing device — which is our ship’s transducer. [That's] what we call it: a multibeam transducer,” says Miles Logsdon, who teaches Ocean Technology at the University of Washington.

Miles Logsdon and Emily Roland examine high-tech imagery of the Puget Sound seafloor.

Until recently, the ocean floor was mapped using a single-beam sonar. The sonar would emit a sound wave and listen for how long it took to return, like an echo. If you know the speed of sound and the time it takes, you can find the distance the soundwave traveled. High-tech multibeam sonar systems work similarly, except instead of just listening for one echo, microphones pick up echos from 426 different locations every second. It reaches out to 500 meters on both sides of the ship. The end result is a high-resolution 3D map that gives us detailed data of what’s happening on the ocean floor.

Video: How does sonar technology work?

Upon reaching the Elwha River area, Roland and the students discover sand dunes that rise up to 125 meters. Roland is impressed with the dramatic features, including exposed bedrock and strong currents.

“The data quality is good and we’re resolving some really interesting seafloor features I wasn’t even anticipating,” Roland says.

Toshi Wozumi, the NOAA scientist on board, agrees. “So far the data coming in is looking good,” he says. “We’ll be able to use it to update our charts.”

Toshi Wozumi from the National Oceanic and Atmospheric Administration (NOAA) examines the mapping data.

In addition to NOAA nautical charts, the mapping data will also be used to help plan for future management of this marine ecosystem. As oceans face unprecedented changes and ecological uncertainty, states are scrambling for ocean data they can use to assess marine health and concerns.

“One of the biggest data needs that’s happening right now is ‘how can we better manage our waters?’” says Logsdon. “And by manage it, I mean fisheries use, recreational use, marine transportation use, cargo vessels.” 

The team also collected sediment samples to help make the connection between the computer data and what’s actually on the seafloor.

Sediment samples were also taken from the bottom of the Puget Sound seafloor.

“When we can help decision makers see critical areas, it makes me feel pretty good about what we’re doing right?” says Logsdon.


Made possible in part by

Stacey Jenkins

Stacey Jenkins is the managing producer of Spark Public. She is an Emmy-award winning producer who is passionate about pushing the boundaries of digital media and training the next generation of multimedia journalists. Stacey has been a Digital Content Producer at KCTS 9 for the past four years; her stories have been showcased locally on IN Close as well as nationally on SciTech Now and the PBS NewsHour's Art Beat. Stacey’s experience also includes working as a senior producer for KPTS, as an assistant media instructor and producer for Portland Community College and a TV news reporter for the CBC in Canada.

Fun Fact: Stacey’s guilty pleasures include over-the-top Halloween decor, eating sweetened condensed milk straight from the can and Maroon 5’s “Sugar” video.

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