Multibeam SONAR
A significant advance over side-scan SONAR, multibeam SONAR employs a multitude of individual SONAR beams to ensonify the seafloor. This type of SONAR transducer (multibeam echosounder) can be mounted on a towfish, the hull of a ship, a remotely operated vehicle (ROV) and many other types of platforms.
Multibeam, or swath, SONAR systems provide fan-shaped coverage of the seafloor (similar to sidescan SONAR), but the output data is different. Instead of continuously recording the strength of the return echo, the multibeam system measures and records the time for the acoustic signal (ping) to travel from the transducer to the seafloor and back and therefrom deriving distance to the seafloor. Using distance and the transmission angle from the transducer, depth of the seafloor at each beam can be determined. Place these beam points (up to 256 for some multibeam echo sounders) in a line and a contour for each ping is developed. Place these contours side by side and a 3D representation of the seafloor is developed.
Some advantages of multibeam systems over conventional systems include increased detail of the seafloor (100 percent coverage), confidence that all features and hazards are mapped without voids, the ability to map inaccessible areas (e.g., under jetties, structures, and vessels near breakwaters, shoal areas, and retaining walls), fewer survey lines (which translates into less required survey time), optimum seafloor detail for route and dredge programs, and the ability to comply with the highest order International Hydrographic Organization (IHO) and U.S. Army Corps of Engineers (USACE) hydrographic standards.
