A Method for Estimating the Standard Deviation of Wind Directions

Abstract

A method for estimating the standard deviation of horizontal wind directions (σ?), from the cosines and sines of direction angles, is proposed. The advantage of the method is that it can be implemented in a low-cost microprocessor system interfaced to a wind vane transducer in the field. Digitized values of wind direction angles can be processed as they are sampled allowing for the calculation and storage of σ? at the end of each sampling period. There is no need to store or group individual wind direction data or to make any allowance for the 0?360° discontinuity in the wind direction variable. The application of the method to normally distributed direction angles was investigated theoretically. The estimator tends to underestimate σ? with the bias increasing as σ? increases. The bias is small enough to be neglected in the application to wind measurements.