Errors in Wind Measurements Estimated by Five-Beam Phased Array Doppler Sodar

Abstract

Estimation of the errors in sodar wind measurements using the phased array Doppler sodar operated under five-beam observation has been made. When compared with the sonic anemometer on the tower nearby, the variances or second-order moments of sodar-derived horizontal wind, σu and σ??, are about twice as large as those measured at the tower, even though the mean horizontal wind u and the second moment of vertical wind σw are in reasonable agreement with the tower. The random errors in the measured wind variances, which can be separated in the five-beam detection system, are estimated to be about 0.41 m s?1 for the vertical component and 0.46 m s?1 for the tilted beam axis component. If the compensation is made for each component along the antenna beams, the horizontal wind variances averaged over 60 min agree with those values obtained by the sonic anemometer on the tower. An analysis of the power spectra suggests that the discrepancies in σu and σ? are mainly caused by the excess of sodar spectral density in the frequency range higher than about 0.002 Hz.