A systematic search of a charted feature's position and a surrounding radius, with coverage good enough that the feature could not have been missed. Features labelled PA (position approximate), PD (position doubtful) or ED (existence doubtful) often come from unverified reports and are prime candidates. If nothing turns up, the survey recommends deletion; if something does, the work becomes a development.
Disproval on the ED rock is done, 200 metre radius, full multibeam and side-scan, nothing there.
Set the search radius from how the feature was first positioned; a report from a fishing boat using dead reckoning deserves a much wider search than one fixed by GNSS.
Also heard as
- disprove
- disproval search
Related terms
Development
Extra survey work over a feature or shoal to pin down its least depth, shape and extent.
Coverage
The portion of the seabed actually measured or imaged by a survey, expressed as a percentage of the area.
Wreck
The remains of a sunken vessel, charted as a hazard or a feature depending on its depth and size.
Nautical chart
A map of waters and coasts made for mariners, showing depths, hazards, aids to navigation and landmarks.