Original paper

Corrections to sodar Doppler winds due to wind drift

Bradley, Stuart; Strehz, Alexander

Meteorologische Zeitschrift Vol. 24 No. 6 (2015), p. 605 - 614

14 references

published: Nov 5, 2015
published online: Nov 14, 2014
manuscript accepted: Aug 7, 2014
manuscript revision received: Aug 7, 2014
manuscript revision requested: Aug 7, 2014
manuscript received: Jun 20, 2014

DOI: 10.1127/metz/2014/0627

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Refraction of the acoustic beam from a sodar, or translation of the beam due to the wind (known as wind drift), both affect the scattering angle and hence the Doppler shift of the return signal. Wind drift has been the subject of a number of previous studies, which have shown that errors increase with wind speed, giving about 6 % error in the estimated wind speed when the actual wind speed is 7 ms−1. Since previous studies have not treated the general case of finite angular beam width, a new analytic treatment is given here for monostatic sodars. Surprisingly, it is found that the Doppler error contributed by the transmitted beam is exactly compensated by the Doppler error contributed by the received beam, if the two beam widths are the same. If the transmitter beam width is not equal to the receiver beam width, then either over-estimation or under-estimation of wind speed results, depending on which beam is wider. This has implications for bi-static sodars, in which it is not possible to match beam widths. Contrary to this new theory, examples of field comparisons with mast instrumentation show a non-linear relationship between wind speeds measured by a sodar and wind speeds measured by mast-mounted instruments. It is proposed that this is due to the acoustic baffle clipping the received beam and changing its width, since the received beam must return at lower elevations from scattering downwind. This is shown to be feasible for a Metek sodar. The sign and magnitude of the observed non-linear dependence of estimated wind speed on actual wind speed are consistent with this proposed mechanism.


Sodar accuracyDoppler errorwind driftacoustic beam translation