The step that turns a beam's echo into a range. Near nadir, multibeams typically use amplitude detection, finding the centre of the strong echo envelope. Toward the outer beams the echo smears across many samples, so phase detection, which tracks where the phase difference between two halves of the receive array crosses zero, gives better results. Bad detections show up as fliers, steps and noisy swath edges.
Check the bottom detection flags, the outer beams on the slope are all phase and they look jumpy.
Also heard as
- bottom detect
- detection
Related terms
MBES
Multibeam echo sounder: a sonar that measures a fan of depths across the track on every ping, covering a wide swath.
Flier
A spurious sounding that sticks out shoaler or deeper than the real seabed, usually from noise or a false detection.
Nadir
The point on the seabed directly beneath the sonar, where the beam looks straight down.
Bottom pick
The depth chosen from an echo trace as the true seabed, either by the sounder's tracker or by an operator.