Multibeam sonar, an echo sounding technology commonly used to map the seafloor, can also be used to map and detect gaseous seeps in the water column, according to scientists testing the technology on board NOAA Ship Okeanos Explorer last week in the Gulf of Mexico. Unlike other types of sonar, multibeam technology is able to survey a wide area of the seafloor and water column.
The ship's multibeam system produced data to make high-resolution maps of gas in the water column in depths ranging from 3,000 to 7,000 feet (1,000 to 2,500 meters).
"This capability will help increase our knowledge of the marine environment, including the distribution of natural sources of methane input into the ocean and the identification of communities of life that are often associated with methane gas seeps," said Thomas Weber, Ph.D., of the University of New Hampshire's Center for Coastal and Ocean Mapping and lead scientist of the mission.
A perspective of the seafloor showing preliminary results of gas seeps detected NOAA Ship Okeanos Explorer multibeam sonar in vicinity of Biloxi Dome in Northern Gulf of Mexico. Gas seep locations are shown as blue dots and are overlaid on the seafloor bathymetry that was collected.
(Credit: Image produced by the University of New Hampshire Center for Coastal and Ocean Mapping / Joint Hydrographic Center using IVS Fledermaus software.)With the Gulf of Mexico home to numerous gaseous seeps, data collected by multibeam sonar could prove valuable to researchers planning further studies of gas seeps and their effects on the marine environment.
The objective of the expedition was to test the sonar's ability to map gaseous seeps, not oil, as oil is more difficult to acoustically detect with the multibeam sonar. Techniques developed during this cruise are intended to help scientists better understand detection of gas seeps which may in turn better inform scientists who are working on techniques to map oil in the water column.
"Mapping the seafloor and the water column are essential first steps in exploring our largely unknown ocean," said Weber. "This expedition confirms earlier indications that multibeam technology provides a valuable new tool in the inventory to detect plumes of gas in the water column, and especially in deep water."
The expedition was conducted jointly by NOAA's Office of Ocean Exploration and Research (OER), the University of New Hampshire's Center for Coastal and Ocean Mapping, and the Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE), as well as scientists and technicians from NOAA's Southeast Fisheries Science Center working in parallel from NOAA Ship Pisces.
"In 2009, we were testing Okeanos Explorer's multibeam sonar off the U.S. West Coast when the sonar first displayed its potential to acoustically map the water column," said Mashkoor Malik, a physical scientist with NOAA's OER and expedition coordinator for the mission. "The sonar mapped a plume of suspected methane gas that rose 4,200 feet (1,400 meters) from the seafloor. But this expedition in the Gulf was the first comprehensive test of Okeanos Explorer's multibeam to detect deep gaseous seeps over a wide area. Its use during this mission confirms the effectiveness of the tool and may lead to extending NOAA's water-column mapping capabilities."
A view of the multibeam sonar water column backscatter data used to detect gas seeps. Gas seeps derived from the sonar are shown in the foreground.
(Credit: Image produced by the University of New Hampshire Center for Coastal and Ocean Mapping / Joint Hydrographic Center using IVS Fledermaus software.)Single beam sonar systems have been used extensively to map gas seeps but do not provide as much coverage as typically collected by multibeam systems. Since multibeam sonar obtains information from a wide fan-shape of beams, it maps a wider area more quickly and efficiently. The multibeam sonar on Okeanos Explorer is one of the few that is specially configured to collect water column data to characterize gaseous seeps in wide areas of the deep-ocean's water column in high resolution.
Bill Shedd, a BOEMRE geophysicist and expert in hydrocarbon seeps who participated in the expedition as part of an ongoing collaboration with NOAA's OER, stated, "Our agencies have been working together in the Gulf of Mexico since 2003. We're optimistic and impressed about this new capability for exploration that was demonstrated so well during this expedition."
NOAA Ship Okeanos Explorer is operated, managed and maintained by NOAA's Office of Marine and Aviation Operations, which includes commissioned officers of the NOAA Corps and civilian wage mariners. NOAA's OER owns and is responsible for operating and managing the cutting-edge ocean exploration systems on the vessel. It is the only federal ship dedicated to systematic exploration of the planet's largely unknown ocean.
Observing 10 years of ocean exploration, NOAA OER uses state-of-the-art technology to explore Earth's largely unknown ocean in all its dimensions for the purpose of discovery and the advancement of knowledge. Expeditions are chronicled at oceanexplorer.noaa.gov, with images and logs from sea.