Total vertical uncertainty is the vertical component of total propagated uncertainty, stated at 95 percent confidence. Survey standards set the allowed maximum as the square root of a squared plus (b times depth) squared, where a is the fixed part and b scales with depth. For Special Order, a = 0.25 m and b = 0.0075, which allows about 0.29 m at 20 m depth. Tide or datum error, sound speed and heave usually dominate the budget.
Allowable TVU at 30 metres is about 0.34 for Special, and we're sitting at 0.22, so plenty of margin.
Also heard as
- total vertical uncertainty
Do not mix it up with
- THU: THU is the horizontal position uncertainty of a sounding; TVU is its depth uncertainty.
Related terms
TPU
Total propagated uncertainty: the combined estimate of how far each sounding could be from the truth, at 95 percent confidence.
THU
Total horizontal uncertainty: how far a sounding's true position could be from where it was recorded, at 95 percent confidence.
Special Order
A survey order for harbours and channels where under-keel clearance is critical, with full coverage and 1 m feature detection.
Tide correction
The adjustment that removes the height of the tide from measured depths so they refer to chart datum.