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This facility, created by the IERS GGFC Special Bureau for Tides, allows users to predict tidal variations in Earth's rotation rate based on the harmonic constants of 8 short-period (diurnal and semidiurnal) tidal constituents. The default harmonic constants are for UT1 variations implied by the ocean tide model that was adopted for the IERS 1996 Conventions. Harmonic constants for other models can be entered as desired. An hourly time series of tidal variations is computed for the desired timespan.
The user need not understand anything at all about tidal phase conventions in order to generate tidal predictions. Moreover, it is clear that this facility can be used to predict ANY tidal time series, e.g., sea level, gravity, etc., not just UT1 variations. The user only has to enter the appropriate tidal constants. This program uses strictly the Doodson convention for tidal phase lags and it uses strictly UTC for time.
Since this facility is part of the IERS GGFC, it is most appropriate for predicting tidal variations in Earth rotation. If you're interested in predicting sea level variations, then you could enter harmonic constants (by hand) for your port of interest. Such constants are available, for example, from NOAA. However, our prediction algorithm is not geared for the typical long lists of harbor harmonic constants, so the prediction (based on only the 8 primary tides) won't exactly agree with NOAA predictions. This is especially so for ports displaying large nonlinear tides. If you are primarily interested in sea level, try using David Flater's Xtide package. There are also some web sites that run Xtide interactively, e.g., the site at coconet.com.
A word concerning the prediction algorithm.... Although the harmonic constants for only 8 tidal constituents are user input, the prediction algorithm uses these 8 constituents to infer (by linear admittances) the constants for another 16 minor constituents. In addition, it applies nodal modulations for all lunar tides. Thus, although only 8 tides are entered, approximately 50 tidal spectral lines are used in the prediction. But no long-period tides are included. The longest-period tidal constituent included (by inference) is 2Q1 (period 28.007 hours).
