We made it to international waters last night and dove right into mapping. The ocean is so vast that very little of its floor has been mapped. Whenever this ship crosses the ocean, it turns on a sonar device attached to the bottom of the ship to collect information about the water depth and the shape of the seafloor. This information is shared world-wide to map the entire ocean floor. We’re collecting seafloor data using the ship’s built in multibeam echosounder.
Multibeam is a type of sonar used to map the seabed. It’s called multibeam because it sends out many beams of soundwaves at once to cover a wide section of the seabed as the ship passes over. Take a look at the artist’s conception of multibeam sonar in the image below. The device is mounted to the hull of the ship and emits soundwaves in a fan-shaped pattern. The soundwaves bounce off the seafloor back toward the ship. The time it takes the soundwaves to hit the seafloor and bounce back to the ship is measured and used to calculate the depth of the ocean floor below the ship.
The receiver can interpret many soundwaves at once because it uses beamforming. Beamforming controls the phase (timing) and amplitude (wave height) of the signal at each transmitter, creating many unique signals, so the receiver can determine the direction as well as depth. Computer software processes the information in real time generating colored maps as the ship moves along. Red represents shallow depths and blue or purple represents deeper areas. The multibeam topographic maps have a resolution of about 60 meters and are used to locate areas of interest for further exploration.
Map on!
Sally
(NOS/NCC)S/CCMA Image ID fis01334, NOAA’s Fisheries Collection)
