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If I perform a FFT of a real signal which is limited on time (for example the atmospheric pressure in time from 0s to 5000s), is it possible that the fact that is limited on time can affect the FFT results? I read this thread and I don't know a priori how many cycles can fit inside it. Is it possible that spectral leakage occur? In the end it is like a big rectangular window.

Are there ways to overcome the effect of the limited sampled signal length?

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This is a recurring question on the website, and I'm sure if you search for "spectral leakage" here, there are PLENTY of resources available such as here and here

Answer to your question is, yes, there are ways to diminish the effects of spectral leakage using windows different from the regular rectangular window.

This is a good resource for learning about what spectral leakage is, and ways to deal with it.

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    $\begingroup$ Nice link! I hadn't seen that before. $\endgroup$
    – Peter K. ♦
    Commented Dec 16, 2022 at 12:48
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    $\begingroup$ If I don't want to divide my signal in windows is still possible to diminish the effect of the spectral leakage? $\endgroup$
    – user49811
    Commented Dec 16, 2022 at 12:55
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    $\begingroup$ Hanning is a major modification of the signal, I'd say introduces more distortions to FFT than it alleviates. A flattop that decays near edges, like Tukey, preserves most of time-frequency behavior and should hold beyond idealized cases. $\endgroup$
    – OverLordGoldDragon
    Commented Dec 16, 2022 at 13:08
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    $\begingroup$ Yes, except it doesn't have to be a hanning window. As @OverLordGoldDragon suggests, try a Turkey window! It will only attenuate the signal near the edges, unlike a hanning window which is more useful with window-overlap methods. My answer has links that can help you decide what window you can use. $\endgroup$
    – Jdip
    Commented Dec 16, 2022 at 13:17
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    $\begingroup$ The Tukey window is really relegated to transient events where we are interested in accurately capturing the amplitude over a short interval in time, it has great freq resolution for the main-lobe but comes at a cost of very poor sidelobe suppression in frequency compared to other windows. See this classic paper by fred harris which covers using different windows in many applications, in particular Fig 12 is interesting in stacking up the Tukey vs Hamming Windows. For optimum time bandwidth resolution, the Kaiser window is a great choice and DPSS is optimum when processing allows. $\endgroup$
    – Dan Boschen
    Commented Dec 17, 2022 at 21:42

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