.Explaining the Y-Axis Units of Spectrum Density Calculated by MATLAB

[luismillan]

Recently we have received a revision of one manuscript. One reviewer request an explanation of the units of the y-axis of the spectrum density (calculated through fft MATLAB algorithm). As we are not physics or mathematic we have troubles to perform an appropriate response.


The units that we give in our manuscript are mm2 (the time series units is mm).


We add the MATLAB algorithm and our MATLAB text lines.


[Frd,Crd]=size(RD);

nfft=2^nextpow2(Frd);

fftrd2=fft(RD,nfft); fftrd=fftrd2(1:nfft/2,:); fftrd=abs(fftrd)

were RD is the time serie.




I grateful if anyone guide me about it

 

[Valerie Park]

. The units of the y-axis of the spectrum density are determined by the units of the time series and the number of samples (N) used in the computation. The spectrum density is calculated as the square of the absolute value of the FFT divided by N. Therefore, the units of the y-axis of the spectrum density would be mm2/N.