The intensity of the echo returned toward the sonar, logged by multibeam and side-scan systems along with the travel times used for depth. Hard, rough bottoms such as gravel and rock return strong backscatter, soft mud returns weak backscatter, and incidence angle changes the level a great deal. Once corrected for gain, power, beam pattern and grazing angle, it is mosaicked into an image used for habitat maps, sediment classes and spotting debris.
Backscatter jumps right at the old disposal site boundary, that's coarse dredge spoil over mud.
Changing power, gain or pulse length mid-survey creates seams in the mosaic that look like geology, so lock the settings or log every change.
Also heard as
- BS
- acoustic reflectivity
- intensity
Related terms
MBES
Multibeam echo sounder: a sonar that measures a fan of depths across the track on every ping, covering a wide swath.
Side-scan sonar
A sonar that images the seabed to either side of its track, revealing objects and textures by their echoes and shadows.
Bathy
Clipped form of bathymetry, used for depth data, depth surfaces or the depth-measuring part of a job.
Fluff
A soft, fluid mud layer over the firm seabed that gives different depths at different sonar frequencies.