Multibeam sonar

Multibeam sonar is an active sonar system used to map the seafloor and detect objects along the seafloor.
Multibeam sonarMultibeam sonar

What is multibeam sonar

Multibeam sonar is used to map the seabed. Like other sonar systems, multibeam systems emit acoustic waves in a fan shape beneath the multibeam sonar’s transceiver (a combined radio transmitter and receiver). The time it takes for sound waves to reflect off the seabed and return to the receiver is used to calculate the water depth.

Multibeam sonar systems use beamforming to extract directional information from the returning soundwaves, producing a swath of depth readings from a single ping. Because of its multibeam configuration, the sonar can map a swath of the seafloor rather than just mapping a single point.

How they work

A multibeam array is usually mounted directly on the ship’s hull.

Different frequencies are used to map different water depths, with higher frequencies (more than 100kHz) used for shallow water and low frequencies (less than 30 kHz) for deep water. There is also a trade-off in resolution with different frequencies, with higher frequency systems providing greater spatial resolution than lower frequency systems.

Multibeam sonars also can collect backscatter measurements for features that reflect sound in the water column. Water column backscatter data can be used to reveal objects in the water column, such as three-dimensional structures associated with shipwrecks, bubble plumes emanating from the seafloor, and dense layers of biology.

Scanning with Multibeam Bathymetry. Credit: Wessex Archaeology
Scanning with Multibeam Bathymetry. Credit: Wessex Archaeology

Why is it important

A multibeam sonar survey is one of the first tasks used to explore new underwater areas. After determining the seafloor’s depth, shape, and character, scientists can plan more comprehensive dives for ROVs.

Scientists discovered multibeam patterns of sediment and the character of sediment identified by multibeam, and verified with ROV video imagery, also gives clues to what organisms may live in the area and aids in the process of habitat suitability mapping.

Initial multibeam mapping lays the foundation for answering more specific exploration and research questions about our ocean.

Multibeam bathymetry. Credit: the NOAA Office of Ocean Exploration and Research, Windows to the Deep 2019

About the images
RWMT work with nation states, government agencies and institutions on sensitive and often classified operations. Also, the tools we use are constantly being evaluated and changes depending on the nature of the operation. Because of this, we have sometimes chosen to show example images of the tools we use, rather than images from actual projects.

Used for

Mapping the seafloor
Localization of objects

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