spectrum analysis of wind

Hello every one.

I am having Wind hourly data. Now I want to know spectral analysis of wind for cycles/day..

could any one help me out.. It would be better appreciation.

Thanks in advance.. phanindra

Answer 1

[Wayne King]

If you have the Signal Processing Toolbox, you can use periodogram() to get a power spectral density estimate of the wind data in cycles/day. periodogram() is nice because it will output an appropriate frequency vector for you and confidence intervals if you desire.

I'll show you how to do that with your sampling frequency, 1 sample/hour. I'll have to simulate some data because you did not attach yours.

30 days of data:

   t = 0:1:(30*24)-1;
     x = 1.5*cos(2*pi*(1/24)*t)+randn(size(t));  % 1 cycle per days plus noise
     [Pxx,F] = periodogram(x,rectwin(length(x)),length(x),1);
     plot(F*24,10*log10(Pxx))
     xlabel('Cycles/Day'); ylabel('dB');

Otherwise, you can use fft() in base MATLAB, to the same in base MATLAB, see

PSD using FFT

[reddy]

hello Wayne King..

Thank you for your reply. I am having data starting from odd hours and ends at odd hours. any ways I will choose from 00 hours only.

And I did understand still could you please let me know how to handle this data set which i am attaching

thanks in advance..

Answer 2

[Wayne King]

You don't really have a lot of data here. If you just choose from 0:00 you only have 42 samples.

Even taking all the data, I don't see a strong periodicity here. You have a non-zero mean (DC component). If you remove that, there is some oscillation around 0.015 cycles/hour or 0.36 cycles/day, but your frequency resolution is just 1/55, so I wouldn't feel too confident about that (given that you had a non-zero mean). Bottom line, you need more data.

    [data,txt] = xlsread('Book1.xlsx');
    [Pxx,F] = periodogram(data-mean(data),[],256,1,'centered');
    plot(F,Pxx)
    xlabel('Cycles/hour')

[reddy]

hey Wayne King

Okay I am attaching the entire data so you please tell me how to handle this data..

[data,txt] = xlsread('Book1.xlsx'); [Pxx,F] = periodogram(data-mean(data),[],256,1,'centered'); plot(F,Pxx) xlabel('Cycles/hour')

When I am using the above code what you have given I am getting error like

[data txt] = xlsread('wind.xlsx');

[Pxx,F] = periodogram(data-mean(data),[],256,1,'centered'); Error using periodogram (line 110) Ambiguous or invalid string option specified.

help me out

thank you in advance

[Wayne King]

which version of MATLAB are you using, you must have an older version.

plus you have 87 NaNs in your data, what do you propose to do about those?

[reddy]

Hi Wayne king

I can not change those NaN values. I want to leave those NaN fields like that only.. And I am having 2011 Matlab.. I have 2009 also but I am not using it..

So what do you suggest Mr.Wayne King.

[reddy]

hi Wayne King one more help

I got the plots with your earlier suggestions.. Thank you for that. and now you look into the attached

 figures and let me know how to get the same spectral analysis plots.

Thanks in advance.

Answer 3

[Bjorn Gustavsson]

Have a look at the circular statistics toolbox available at the FEX: http://www.mathworks.com/matlabcentral/fileexchange/10676-circular-statistics-toolbox-directional-statistics