Beam Geometry Calibration of Sodars without Use of a Mast

Abstract

new method for calibration of sodar wind speed measurements is described. The method makes no assumptions whatsoever about the sodar operation and its hardware and software, other than the assumption that only one beam is transmitted at a time. Regardless of the complexity of the actual beam shape, the effective beam zenith angle is accurately estimated: this is the angle that must be used in estimations of velocity components. In a very simple experiment, the effective beam zenith angle has been found to within around 0.2°, which is as good as is required in the most stringent sodar calibration procedures. It has been found, even for such a short data run, that the estimated beam angle is very close to that calculated from the sodar array geometry. The main limitation is the requirement for horizontally homogeneous flow, since the regression methods use both a tilted beam and a vertical beam. Note that this is also a fundamental limiting assumption in the normal operation of ground-based wind lidars and sodars.