Find the Frequency Components of a Time Series Graph For a periodic (and not so periodic) function, it is always possible to use Fourier series to find out the frequencies contained in the function.
But what about function that cannot be expressed in mathematical terms? For example, this graph (accelerogram):

Is there anyway to apply a sort of Fourier series, in order to find out the frequencies contained in it?

Quinn and Hannan's The estimation and tracking of frequency is dedicated to this topic. I can highly recommend it.
