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Well, no one "detects" the various harmonic forces directly. However, note
that, depending on the model, there may be over 100 harmonic terms in the
calculation and according to the data before me the amplitude of the weakest
harmonic considered is 5 or more orders lower than the principal lunar
harmonic, M2. A couple of years ago when this topic was rampaging on the
list, I made a calculation of the principal Venus force, V2 say, and
compared with the lowest order lunar and solar harmonics. I found them to
be comparable. Of zzzzzzzzzzzz I am senile and may have made an error. I
will check.
Tide tables are not generated by doing fourier transforms on tidal data.
They are generated by doing harmonic analysis, quite a different process.
Well they *used to be* harmonic reductions, but I understand they now do a
Fourier transformation -- the result should be the same -- the Fourier
transform should yield the same frequencies as the astronomical force
calculations. The coefficients would need to be empirical in any case. I
will consult with my friend at NOAA and check.