how to distinguish fft frequency is real existence or noise

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peter huang
peter huang 2022-4-16
评论： peter huang 2022-4-18
i useing fft analyze tide water level
i want find exist tide component
but fft present a lot of noise
i want distinguish frequency which is real existence (very likely to exist) or not exist(noise)
how should i distinguish fft produce real frequency and noise
attached file is my plot fft amplitude and frequency

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回答（1 个）

Bruno Luong
Bruno Luong 2022-4-16
You need to have a priori knowledge of the spectrum of the signal and the noise, and design an appropriate noise filter
  • if the noise stectrums are well separated, you are OK
  • if they are partially overlap, you have to make a compromise
  • if they are totally overlapped you are screwed
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Image Analyst
Image Analyst 2022-4-17
@peter huang I don't know what M2 and O2 are. Can you point them out on this diagram?
and, like I asked before, if you're just trying to find really tall peaks less than 0.1, then what does it matter if there is noise? Those peaks could still be found without any denoising.
Even if you did want to do denoising, wouldn't it make sense to do it on the original data instead of the Fourier Transform of the data?
peter huang
peter huang 2022-4-18
@Image Analyst
I understand what you mean so I probably don't need to do the denoising
The m2 period is about 12.45hr which is clearly the most prominent point in the graph
Maybe the real tidal component will be very prominent (large amplitude) in fft
How do I now filter out the other sub-tide so that only the larger amplitude values ​​are left?

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