I have a set of time series data for a single year (365 records). The objective is to calculate the anomalies in the values. However, anomalies are not defined as the differences from the mean. Anomalies are defined as the difference from a baseline which in turn is defined as the sum of annual and semiannual harmonics.
Is there a possible way to extract the annual and semiannual harmonics of the time series data preferably using python?
Simply, You can apply FFT to your time series data, as result you will get periodicity (if any). There are number of packages available in python e.g. numpy, scipy which can perform fft. Below are some useful links for fft using python.
https://stackoverflow.com/questions/25735153/plotting-a-fast-fourier-transform-in-python
https://www.ritchievink.com/blog/2017/04/23/understanding-the-fourier-transform-by-example/
Hope this will help.
I have been trying the same for days. I think I'm stuck. I will now upload a plot to make it a bit more lucid.
I still don't understand how does the author get a smooth line. Hope you understand my concern now.
The right side plot you show is not fit with fft but it is just a spline fit (thick line).
As one can see in smooth line the one cycle from feb to Jan which is annual cycle.
So don't be confuse as this figure is not for fft, it's just time series with smoothing/fitting.
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