# how to use the hanning window to smooth the photon signal

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yuxuan 2024 年 2 月 19 日
コメント済み: Star Strider 2024 年 2 月 20 日
windowLength = 91;
hannWindow = hann(windowLength);
smooth_data = conv2(data, hannWindow, 'same');
is the code correct? Because when i increase the windowlength, the smooth_data will increase as well

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### 回答 (2 件)

Alexander 2024 年 2 月 19 日
I can't see this effect you mentioned. smooth_data remains the same size as data (I assume data = Photoncounts1). What do you expect? I never used windowing in the manner you have done it in the code above. Usually I multiplied the data with the window (or parts of the window) in the time domain to get rid of the step function and having a clear transient effect before a fft. Just an example:
clear;
N = 1024;
x = 0:N-1;
Whann = hann(N)';
y = rand(1,N); % Create some data
subplot(211);
plot(x,y);title('Original');grid minor;
subplot(212);
plot(x,y.*Whann);title('Windowed');grid minor;
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Alexander 2024 年 2 月 20 日
Once again: A hann window is not made for smoothing data, but to minimize the effect of a rectangular function (start of measurement <-> end of measurement) in the time domain. If your signal is time domain data, use a filter.
yuxuan 2024 年 2 月 20 日
The following sentences are what i found in eassys about using hanning window to smooth data:
'vertically smoothed by a running Hanning window with FWHM width of 2 or 1 km'
'smoothed by sliding a 2‐km full width at half maximum (FWHM) Hanning window in the vertical direction in the temperature retrieval process '
'The smoothing of the signal plus background is by a Hanning filter with a 2-km FWHM window'

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Star Strider 2024 年 2 月 19 日
That appears to be some sort of spectrum. I am not certain what you want to do with it, however windowing it is not likely to produce any benefit at this point.
% whos
figure
stairs(Photoncounts1)
grid
xlabel('Bin (?) Frequency (?)')
ylabel('Counts')
title('Photons')
xlim([0 600])
If this is a Fourier transform, the time to window the data was before calculating the transform.
.
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yuxuan 2024 年 2 月 20 日
Star Strider 2024 年 2 月 20 日
Thank you!

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