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q |
Integer values of k have no specific meaning. They are
determined
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based on the length of the observation period T (=NDt):
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k = (0,
1, 2, 3,..N/2) cycles during the period T.
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q |
Since we use N observations to determine a mean and N/2
line spectra,
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each line spectrum has only about 2 degrees of freedom. With such
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small dof, the line spectrum is not likely to be reproduced from one
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sampling interval to the other.
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q |
Also, most geophysical “signals” that we are interested
in and wish to
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study are not truly “periodic”. A lot of them are just
“quasi-periodic”,
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for example ENSO. So we are more interested in the spectrum over a
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“band” of frequencies, not at a specific frequency.
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