Sonar Tests Underwater Oil
Researchers compared the performance of acoustic and optical instruments using this oil slick in the Ohmsett wave tank.
CREDIT: Paul Panetta
Two years after the Deepwater Horizon oil spill in the Gulf of Mexico, researchers are developing a way to test whether deep-sea chemical dispersants work to break oil up into tiny droplets. It may seem like a simple issue, but nobody actually knows whether dispersants used deep underwater are effective. Now researchers at the Virginia Institute of Marine Science are trying to test the size of underwater oil drops using sound waves, which penetrate water better than the light waves current measuring methods use. “There’s a reason that many marine mammals use sound rather than sight for long-distance communications,” said Carl Friedrichs, a marine scientist who is a part of the project.
In the past, companies sprayed dispersants on the surface of the sea to break oil up into tiny droplets less than one-tenth of a millimeter across. Smaller droplets make the oil easier for bacteria to break down. They also mix more easily with seawater, reducing the oil’s effects on seabirds and turtles.
Before the Deepwater Horizon spill, however, no one had ever used dispersants deep underwater like BP did, Woods Hole Oceanographic Institution scientists wrote in a paper published in the journal Environmental Science & Technology. Even a year after the spill, researchers weren’t sure how much BP’s dispersants worked to break up the gushing oil and how much improvement was simply due to time and physics, one Woods Hole scientist told Greenwire.
Virginia Institute of Marine Science researchers have done three tests of their sonar measuring method in huge tanks in New Jersey and Norway that can hold millions of gallons of water. They’ve found sound waves do penetrate thick, dark oil plumes better than the lasers, called LISSTs, that scientists now use to measure oil on or just below the surface of the ocean.
The U.S. Department of the Interior, along with the marine science institute’s industry partnership office, is funding the research.
Next, the research team will need to create a way to measure the exact size of oil droplets, said Paul Panetta, another institute scientist who is part of the project. The team hopes to create a measurement method that can tell companies when they’ve used enough dispersant and help researchers track the movement of oil through the ocean after a spill.