The basic unit of hydrography: one depth tied to one position and time. A large multibeam survey produces billions of soundings, which are cleaned, reduced to datum and gridded. On a chart, soundings are the depth figures selected from surveys and shown below chart datum. Seafarers say a ship is on soundings when the water is shallow enough to reach bottom with a lead.
Pull the shoalest sounding in that 5 metre box and send it with the DtoN.
Also heard as
- depth
- spot depth
Related terms
Bathymetry
The measured depth and shape of the seabed, or the work of measuring it.
Sounding selection
Choosing which surveyed depths appear on a chart so the shoalest water is always shown.
Lead line
A marked line with a lead weight on the end, used to measure depth by hand and to check echo sounders.
Least depth
The shallowest depth over a wreck, rock or other feature, which is the value that gets charted.