The standard method for giving a short-term gauge full-epoch datums. Means and ranges observed at the short-term station are compared with those at a nearby long-term control station for exactly the same period, and the differences or ratios are applied to the control station's accepted datums. A month of good data can yield datums useful for surveys; longer records cut the error further.
We'll get MLLW at the new site by simultaneous comparison with the entrance gauge, so we need 30 clean days.
Also heard as
- datum transfer
- comparison of simultaneous observations
Related terms
Tidal datum epoch
The fixed 19-year period over which water levels are averaged to compute official tidal datums.
Reference station
A tide or current station with its own harmonic constants, for which full daily predictions are published.
Tidal datum
A local zero for heights, computed by averaging one stage of the tide, such as high or low water, across many years.
Staff shot
A set of tide staff readings taken alongside the gauge to check that the gauge is still reading true.