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3.5.3 Step 3: Initial Detiding
This step removes the tidal contribution from the pressure record (despiked but
still containing drift) using a FORTRAN program called RESPO.for (Response Analysis
of Tides), based on the work of Munk and Cartwright (1966). Response analysis
constructs and applies a predictive filter which represents the ocean’s response to
gravitational forcing. Unlike the related harmonic analysis, the response analysis assumes
nothing about which frequencies are present, because the input function is derived
directly from Newtonian-Keplerian orbital motions; the input function contains all the
variations of the astronomic forcing regardless of size. The oceanic response is
considered distinctly from the astronomic forcing. The method also has a more physical
basis than harmonic analysis since it treats the ocean as a dynamical system. Details of
the response method are given in Appendix C.
A pull down menu provides three tidal prediction options in the
IES_GUIDRIVER window:
Di, Semi-Di, 3 lags (default)
Di, Semi-Di, 5 lags
Di, Semi-Di, Mf, Mssa, 5 lags
where Di refers to diurnal, Semi-Di to semi-diurnal, Mf to lunisolar fortnightly, and Mssa
to solar semi-annual.
The tidal prediction option to use depends on the length of the pressure time
series. Table 3 provides recommended guidelines for choosing the tidal prediction option
from the pull down menu.
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