Comparison of turbulence measurements by a CSAT3B sonic anemometer and a high-resolution bistatic Doppler lidar

Abstract

Accurate measurements of turbulence statistics in the atmosphere are important for eddy-covariance measurements, wind energy research, and the validation of atmospheric numerical models. Sonic anemometers are widely used for these applications. However, these instruments are prone to probe-induced flow distortion effects, and the magnitude of the resulting errors has been debated due to the lack of an absolute reference instrument under field conditions. Here, we present the results of an intercomparison experiment between a CSAT3B sonic anemometer and a high-resolution bistatic Doppler lidar, which 15 is inherently free of any flow-distortion. This novel remote sensing instrument has otherwise very similar spatial and temporal sampling characteristics as the sonic anemometer and hence served as a reference for this comparison. The presented measurements were carried out over flat homogeneous terrain, at a measurement height of 30 m. We provide a comparative statistical analysis of the resulting mean wind velocities, the standard deviations of the vertical wind speed and the friction velocity and investigate the reasons for the observed deviations based on the turbulence spectra and cospectra. Our results 20 show a very good agreement of the mean wind velocity measurements and the standard deviations of the vertical wind speed, with comparabilities of 0.082 and 0.017 m s −1 , respectively. Biases for these two quantities were very low, being smaller than 0.01 m s −1 , which corresponds to about 1 % in relative terms. Slightly larger differences were observed for friction velocity.Analysis of the corresponding cospectra showed that the CSAT3B underestimates this quantity systematically by about 3 % on average as a result of too steep a drop-off in the inertial sub-range. We also found that an angle-of-attack dependent 25 transducer-shadowing correction does not improve this agreement effectively because it leads to an artificial correlation between the three wind components and therefore severely distorts the shape of the cospectra.

Statistics of the Optical Turbulence from the Micrometeorological Measurements at the Baykal Astrophysical Observatory Site

“…However, biases are generally very small for these sensors [9]. Comparative statistical analysis of the mean meteorological characteristics measured by the ultrasonic anemometers with data of the lidars and mechanical anemometers shows a very good agreement [6,7,10,11].…”

High-resolution Bistatic Wind Lidar

“…Overall, although both the PTB bistatic lidar and the employed ultrasonic anemometer have proven to be well suited for measurements in turbulent flow, the PTB bistatic lidar is the more favourable option if high precision is desired. This is due to its distortion-free measurement capability which is free of any angular dependence [3,28].…”

“…Accurate wind velocity measurements are an essential prerequisite for many applications in the field of wind energy and meteorology, like wind potential analysis [1], power curve evaluations of wind turbines [2], and atmospheric turbulence analysis [3]. For example, low measurement uncertainties are especially desired for reliable resource assessments of projected wind farms because the wind turbine power output scales with the third power to the wind velocity [4].…”

How accurate are ultrasonic anemometers, calibrated in a laminar wind tunnel, under turbulent conditions?

“…This is because, IOP Publishing doi:10.1088/1742-6596/2767/4/042023 2 in a non-orthogonal layout, the transducers are not positioned in mutually perpendicular directions, which can introduce complexities and challenges in accurately measuring specific wind components [2,3]. It has also been noted that applying wind tunnel-based corrections to instruments installed in the field can lead to overcorrection, particularly in more turbulent environments [4,5]. Also, [6] highlighted the influence of wind direction on the discrepancies observed between ultrasonic anemometers from different manufacturers.…”