The classic hydrographic sounder: one transducer sends a pulse straight down and times the echo to give one depth. Survey models are often dual frequency, pairing a high frequency near 200 kHz that reflects off the top of soft sediment with a low frequency around 24 to 33 kHz that penetrates into it. Coverage exists only along each line, so features between lines can be missed, and singlebeam is the usual tool for channel condition surveys and very shallow work.
Singlebeam's showing a metre between high and low frequency, that's fluff over the channel bottom.
Dredging contracts name the frequency that defines the pay bottom, and mixing 200 kHz and 33 kHz data from different contractors puts a false step in the surface.
Also heard as
- SBES
- singlebeam
- single-beam echo sounder
Related terms
MBES
Multibeam echo sounder: a sonar that measures a fan of depths across the track on every ping, covering a wide swath.
Bottom pick
The depth chosen from an echo trace as the true seabed, either by the sounder's tracker or by an operator.
Fluff
A soft, fluid mud layer over the firm seabed that gives different depths at different sonar frequencies.
Bar check
A singlebeam calibration that hangs a plate on marked lines under the transducer and compares the sounder with each known depth.
Splits
Extra survey lines run halfway between existing lines to tighten spacing over a shoal or suspicious spot.