A multibeam echo sounder transmits a fan-shaped pulse and forms hundreds of receive beams, measuring a depth for each beam on every ping. Shallow-water systems work at roughly 200 to 400 kHz and resolve fine detail; deep-water systems use around 12 kHz to reach the abyss. Each depth depends on accurate position, attitude, heading, sound speed and timing, so the sonar is only as good as the sensors and calibration around it.
MBES is pinging at 20 hertz with 512 beams, plenty for feature detection at 15 metres.
Most multibeam problems turn out to be sound speed, timing or offsets rather than the sonar itself, so seasoned processors check the supporting sensors first.
Also heard as
- multibeam
- multibeam echo sounder
- swath sonar
Do not mix it up with
- Side-scan sonar: Side-scan produces an acoustic image of the seabed without reliable depths; multibeam measures a depth for every beam.
Related terms
Swath
The strip of seabed measured or imaged across the track on one line of a multibeam or side-scan survey.
Singlebeam echo sounder
An echo sounder that measures one depth directly beneath the vessel on each ping, using a single vertical beam.
Bottom detection
The method a multibeam uses to pick the instant the seabed echo arrives in each beam and turn it into a depth.
Patch test
A set of calibration lines over flat ground and slopes that measures sonar alignment biases and timing error.
Backscatter
The strength of sound returned from the seabed, used to map bottom type alongside depth.