Mapping the Sound

Students map the seafloor of Puget Sound

Stacey Jenkins KCTS9 .. Watch and Read Online

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.

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.

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.

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.”

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.

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