Multibeam Sonars

Image from tekmap consulting - see link below.

Mutibeam sonars, like side-scan sonars, use swath technology. However, unlike side-scan sonars, multibeam sonars produce better depth (bathymetry) data than backscatter data. Although backscatter is also recorded, the imagery acquired is generally of a lower quality than that recorded from side-scan sonars.

Click image to enlarge.

(Information derived from Acoustic Techniques for Seabed Classification (2005) by J D Penrose, P J W Siwabessy, A Gavrilov, I Parnum, L J Hamilton, A Bickers, B Brooke, D A Ryan and P Kennedy - see link below.)

Mulibeam units may be either mounted on the hull of a ship or mounted in a towfish. They are used to rapidly and accurately map large areas of the sea floor. They can also be used to classify seafloor sediments and locate schools of fish in the water column.

Humminbird 967c 3D

Ocean Ecology has developed a multibeam sonar towfish based on the Humminbird 967c 3D unit.

Ocean Ecology's towfish.

This unit has a traditional downward-looking sonar combined with a multibeam sonar.

Specifications of downward-looking sonar:

• 455 kHz beamwidth at -3dB = 37°
• 83 kHz beamwidth at -3dB = 52°
• Transducer depth range: approximately 300 m at 83 kHz or 75 m at 455 kHz

Specifications of six multibeam sonar beams:

• 455 kHz
  • Horizontal beamwidth at - 3dB = 11°
  • Vertical beamwidth at -3 dB = 11°
  • Transducer tilt angles from vertical = -22.1°, -13.3°, -4.4°, 4.4°, 13.3°, 22.1°
• Transducer depth range: approximately 75 m

Power output of unit:

• 1000 Watts (RMS)

Shown below is a diagram of the beam orientation and coverage for the 3D transducer at -10 dB.

Multibeam beam angles.

Multibeam data will be processed using MB-System, an open source image processing software developed by the Monterey Bay Aquarium Research Institute (MBARI) (see link below).