Oceanographic Tools: Sonar Multibeam
Multibeam Bathymetry -The Successor to the Single-Beam Echo sounding
Multibeam bathymetry is based on the fact that more beams
are better than one. About 30 years ago, the US Navy developed a system that
could send out many beams of sound simultaneously to get a series of water
depth readings along the line of a moving vessel. Instead of just one transducer
pointing down, multibeam bathymetry systems have arrays of 12 kHz transducers,
sometimes up to 120 of them, arranged in a precise geometric pattern on ships hulls.
The swath of sound they send out covers a distance on either side of
the ship that is equal to about two times the water depth. The sound bounces
off the seafloor at different angles and is received by the ship at slightly
different times. All the signals are then processed by computers on board the
ship, converted into water depths, and automatically plotted as a bathymetric
map with an accuracy of about 10 meters.
In this way, ships traveling at speeds over 10 knots can produce a swath, rather
than a line, of water-depth information. Multibeam bathymetry systems are now
routinely used during research cruises to map areas of seafloor as large as thousands
of square kilometers.