A least-squares fit of cosine waves at the known constituent speeds to an observed record, yielding an amplitude and phase lag for each. Record length decides what can be separated: a month resolves the main constituents, while about six months is needed to split S2 from K2 and a year or more to resolve the full set cleanly. The resulting harmonic constants drive predictions and reveal the character of the local tide.
Run a harmonic analysis on the 29 days we have, then predict ahead for the dredge schedule.
With less than a month of data, minor constituents must be inferred from major ones, so short-record predictions are rough guides at best.
Also heard as
- tidal analysis
- harmonic reduction
Related terms
Harmonic constituent
One of the regular cosine waves, each with a period fixed by astronomy, that together make up the tide.
Tidal prediction
A forecast of tide heights or currents computed from harmonic constants and astronomy, with no weather included.
Phase lag
How far a constituent's local high water trails the corresponding astronomical forcing, given in degrees.
Residual
The observed water level minus the predicted tide, showing the effect of weather, rivers and other non-tidal causes.