Multibeam Echo Sounders

Digital Terain Model (DTM) created from multibeam sonar data, draped over nautical chart of Quicks Hole, Mass.

The Office of Coast Survey conducts hydrographic surveys primarily with side scan and multibeam sonars. SONAR (Sound Navigation and Ranging) uses sound waves to find and identify objects in the water and determine water depth.

Multibeam echo sounders (MBES), like other sonar systems, transmit sound energy and analyze the return signal (echo) that has bounced off the seafloor or other objects. Multibeam sonars emit sound waves from directly beneath a ship's hull to produce fan-shaped coverage of the seafloor. These systems measure and record the time for the acoustic signal to travel from the transmitter (transducer) to the seafloor (or object) and back to the receiver. Multibeam sonars produce a “swath” of soundings (i.e., depths) to ensure full coverage of an area. The coverage area on the seafloor is dependent on the depth of the water, typically two to four times the water depth.

Many MBES systems are capable of recording acoustic backscatter data. Multibeam backscatter is intensity data that can be processed to create low resolution imagery. Backscatter is co-registered with the bathymetry data and is often used to assist with bathymetric data interpretation and post-processing.

Graphic depicting multibeam sonar achieving full bottom coverage.

NOAA hydrographic survey units use multibeam echo sounder systems to acquire full- and partial- bottom bathymetric coverage throughout a survey area, to determine least depths over critical items such as wrecks, obstructions, and dangers-to-navigation, and for general object detection. NOAA field units use various models of swath-type multibeam systems both hull and pole mounted for hydrographic survey operations. The use of multibeam echo sounder systems must meet specifications outlined in the "NOS Hydrographic Surveys Specifications and Deliverables".