Week 2: Multibeam Sonar
|A multibeam echosounder is a device used by hydrographic surveyors to determine the depth of water and the basic geomorphology of the seafloor.|
Down the hall and into the control room, the two watchstanders turn over their shift. Computer screens fill the room. The multibeam sonar readings are up on the big screen, and are used to determine the depth of the seafloor. We are cruising 105 km (168 miles) due south of the Pensacola pass. Our water depth is 2,906 m or the equivalent of 29 football fields deep.
|View of the control room on the Okeanos.|
|This multibeam screen shows an underwater sediment river.|
As the ship holds its course, from under the ships' hull a sound pulse, or ping, is transmitted through the water column to the seafloor. After the ping bounces off the seafloor the receiver, positioned next to the transmitter. The time it takes for the ping to go to the bottom and return, translates to the depth of the seafloor at that position. When a ping takes longer to return from the seafloor, the depth is greater. A multibeam acoustic sensor can cover a large area, or swath. It has several transmitters and receivers called transducers that change electric pulses to acoustic pulses and vice versa. This allows a large area to be mapped on one heading, or line. The E302 multibeam used aboard the NOAA Okeanos Explorer can generate 486 depth sounding per swath at a rate of 10 swaths per second. This seafloor depth information, or bathymetric data, is used to create the maps produced today. All of this data is publicly available on the NOAA website. The Okeanos-google digital atlas is also a good place to look at survey sites.
Personal Log for Week 2