The point on an echo record accepted as the seabed. A singlebeam sounder digitizes the bottom automatically, but over soft mud, weed or steep slopes the pick can wander into the water column or below the real surface. Processors review the echogram and re-pick wherever the tracker strayed, and a good pick through kelp or fluid mud comes from experience rather than software.
Tracker took the top of the weed bed, I re-picked the bottom on that whole stretch.
Also heard as
- digitized depth
- bottom digitizing
- re-pick
Related terms
Singlebeam echo sounder
An echo sounder that measures one depth directly beneath the vessel on each ping, using a single vertical beam.
Lost bottom
Said when an echo sounder stops tracking the real seabed and reports noise, a second echo or nothing.
Fluff
A soft, fluid mud layer over the firm seabed that gives different depths at different sonar frequencies.
Bottom detection
The method a multibeam uses to pick the instant the seabed echo arrives in each beam and turn it into a depth.