How do I perform Spectral Analysis (FFT, Windowing, Detrending) on Sonic Anemometer Data? I am having trouble with all of the forums that I have looked at thus far.
I have one day's worth of Sonic Anemometer data. I want to see the spectral analysis of this data. When the anemometer data was being logged it appears that the frequency ranges between 31 and 32 hz. I am looking to analyze this data in thirty minute chunks and I would just like some guidance as to how to go about this. 

I have already removed the bad data (stray data points with 98 m/s winds x.x).  I am not sure if I am supposed to detrend the data then apply a Hamming window and take the Fourier transform, or if I'm supposed to just apply the Hamming window and then take the Fourier transform. 

Also should I calculate the sampling frequency for each 30 minute interval since it appears to change or is that change insignificant? (or should I analyze the whole data set together?)

Sorry for the long post but I have been hacking away on forums all week and I cannot seem to find a consistent solution.
take fft of data

let's say data is x = [ 3 4 5 6 6 9  7 ]

take fft

y = fft(x);
shift so -fs/2  to fs/2
y = fftshift(x);
plot mag
plot(abs(y))


see link for help
fft Help