A single deployment of a profiling instrument from the surface to near the seabed and back, giving one sound velocity profile. Crews do a cast at the start of the day, whenever the surface sensor drifts more than a couple of metres per second from the last profile, and whenever they move into different water. Some ships drop underway probes so the vessel can keep running while it profiles.
Surface sound speed has jumped 4 metres a second, stop at the line end and drop a cast.
Cast where the water is most different, off river mouths, across fronts and at the deep end of the area, not just alongside the dock where it is convenient.
Also heard as
- SV cast
- dip
- profile
Related terms
SVP
Sound velocity profile: how the speed of sound changes with depth through the water, measured to correct sonar depths.
Surface sound speed
The speed of sound right at the sonar face, measured continuously so the multibeam can steer its beams.
Refraction
The bending of sonar beams as they cross water layers with different sound speeds, which distorts depths if uncorrected.
Online
On a planned survey line and logging data; going offline means ending the line and closing the file.