The approach leg in front of each line. The coxswain uses it to get straight, at survey speed and on heading, while the motion sensor recovers from the turn and any towed sensor settles. Lines planned without enough run-in give ragged starts and wasted data. A launch needs a few boat lengths; with side-scan it is far longer because the fish lags well behind the turn.
Give me a longer run-in on these, the fish is still swinging when we go online.
Also heard as
- run in
- lead-in
- approach
Related terms
Online
On a planned survey line and logging data; going offline means ending the line and closing the file.
Line plan
The set of pre-planned survey lines, with spacing and orientation, that a vessel follows to achieve the required coverage.
Towfish
A streamlined body towed on a cable behind the vessel that carries side-scan or other sensors close to the seabed.
MRU
Motion reference unit: the sensor that measures a vessel's roll, pitch and heave to correct sonar data.