Thursday, April 18, 2013

How to calculate mean wind direction - average of circular function - Matlab

The calculation of mean wind direction is not just taking the average as they are in radial co-ordinates. In this I will show you how you can calculate mean wind direction with on line formula.

Please note, all the angles are in degrees and Matlab degree trigonometric functions (sind, cosd and atand) have been used in the calculations. The formula is based on the calculation of the mean of the cosines and sines and the taking the arctangent of their ratio.

%Lets say wd is the wind direction array
wd=[0 10 180 170]

%then mean wind direction is given by
meanwd=atand(mean(sind(wd))/mean(cosd(wd)))

% you can use mod function to avoid negative wind direction if north is represented by 0 degree.
meanwd=mod(meanwd,360)

You will get NaN if all the wind directions opposite to each other.
For example wd=[0 90 180 270] or wd=[0 180 0 180] or wd=[1 181]

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