An analysis of  flow distortion in a multipath sonic anemometer

2021 ◽  
Author(s):  
Ebba Dellwik ◽  
Poul Hummelshøj ◽  
Gerhard Peters
Keyword(s):  
Vertical Velocity ◽  
Velocity Component ◽  
Sonic Anemometer ◽  
Three Dimensional ◽  
Turbulence Theory ◽  
Flow Distortion ◽  
Vertical Velocity Component ◽  
Ongoing Research ◽  
Sonic Anemometers

<p>Sonic anemometers provide point observations of the three-dimensional velocity field at high sampling rates and are crucial instruments for understanding and quantifying the fluxes of momentum, energy and scalars between the atmosphere and Earth’s surface. Since the beginning of sonic anemometry 50 years ago, the characterization of flow distortion, i.e. how the instrument structure alters the flow, has been an ongoing research topic. Multi-path sonic anemometry provides a new opportunity to research and understand flow distortion on the vertical velocity component, since several positions in the small measurement volume can be measured simultaneously. In this work, we use data from a flat terrain measurement campaign in 2020, in which several sonic anemometers were mounted on 4m towers placed 4m apart. The analysis is focused on the Multipath Class-A sonic anemometer (Metek GmbH, Germany), which provides vertical velocity observations from three vertical paths 120 degrees and 0.1m apart. Vertical velocities are also calculated from several combinations of the tilted paths. We investigate how the vertical velocity component is altered depending on wind direction relative to different parts of the instrument structure. We demonstrate that by an optimal combination of the different paths, the vertical velocity variance and fluxes can be significantly enhanced. We also show spectra, and especially look at the high frequency end of the spectrum, where the relative behaviour of the velocity components is known from fundamental turbulence theory. Further, the relative importance of transducer shadowing and pressure-induced blockage effects is discussed.</p>

scholarly journals A method to assess the accuracy of sonic anemometer measurements

2019 ◽  
Vol 12 (1) ◽  
pp. 237-252 ◽  
Author(s):  
Alfredo Peña ◽  
Ebba Dellwik ◽  
Jakob Mann
Keyword(s):  
Power Spectrum ◽  
Sonic Anemometer ◽  
Three Dimensional ◽  
Distortion Correction ◽  
Inertial Subrange ◽  
Flow Distortion ◽  
Three Dimensional Flow ◽  
Sonic Anemometers ◽  
The Usa ◽  
Corrected Data

Abstract. We propose a method to assess the accuracy of atmospheric turbulence measurements performed by sonic anemometers and test it by analysis of measurements from two commonly used sonic anemometers, a Metek USA-1 and a Campbell CSAT3, at two locations in Denmark. The method relies on the estimation of the ratio of the vertical to the along-wind velocity power spectrum within the inertial subrange and does not require the use of another measurement as reference. When we correct the USA-1 to account for three-dimensional flow-distortion effects, as recommended by Metek GmbH, the ratio is very close to 4∕3 as expected from Kolmogorov's hypothesis, whereas non-corrected data show a ratio close to 1. For the CSAT3, non-corrected data show a ratio close to 1.1 for the two sites and for wind directions where the instrument is not directly affected by the mast. After applying a previously suggested flow-distortion correction, the ratio increases up to ≈1.2, implying that the effect of flow distortion in this instrument is still not properly accounted for.

scholarly journals A method to assess the accuracy of sonic anemometer measurements

2018 ◽  
Author(s):  
Alfredo Peña ◽  
Ebba Dellwik ◽  
Jakob Mann
Keyword(s):  
Power Spectrum ◽  
Sonic Anemometer ◽  
Three Dimensional ◽  
Distortion Correction ◽  
Inertial Subrange ◽  
Flow Distortion ◽  
Three Dimensional Flow ◽  
Sonic Anemometers ◽  
The Usa ◽  
Corrected Data

Abstract. We propose a method to assess the accuracy of atmospheric turbulence measurements performed by sonic anemometers and test it by analysis of measurements from two commonly used sonic anemometers, a Metek USA-1 and a Campbell CSAT3, at two locations in Denmark. The method relies on the estimation of the ratio of the vertical to the along-wind velocity power spectrum within the inertial subrange. When we correct the USA-1 to account for three-dimensional flow-distortion effects, as recommended by Metek GmbH, the ratio is very close to 4/3 as expected from Kolmogorov's hypothesis, whereas non-corrected data show a ratio close to 1. For the CSAT3, non-corrected data show a ratio close to 1.1 for the two sites and for wind directions where the instrument is not directly affected by the mast. After applying a previously suggested flow-distortion correction, the ratio increases up to ≈ 1.2, implying that the effect of flow distortion in this instrument is still not properly accounted for.

scholarly journals Field intercomparison of prevailing sonic anemometers

2018 ◽  
Vol 11 (1) ◽  
pp. 249-263 ◽  
Author(s):  
Matthias Mauder ◽  
Matthias J. Zeeman
Keyword(s):  
Wind Speed ◽  
Sonic Anemometer ◽  
Three Dimensional ◽  
Buoyancy Flux ◽  
Horizontal Wind ◽  
Horizontal Wind Speed ◽  
Sonic Anemometers ◽  
Adjacent Structures ◽  
Mean Wind Speed ◽  
Field Intercomparison

Abstract. Three-dimensional sonic anemometers are the core component of eddy covariance systems, which are widely used for micrometeorological and ecological research. In order to characterize the measurement uncertainty of these instruments we present and analyse the results from a field intercomparison experiment of six commonly used sonic anemometer models from four major manufacturers. These models include Campbell CSAT3, Gill HS-50 and R3, METEK uSonic-3 Omni, R. M. Young 81000 and 81000RE. The experiment was conducted over a meadow at the TERENO/ICOS site DE-Fen in southern Germany over a period of 16 days in June of 2016 as part of the ScaleX campaign. The measurement height was 3 m for all sensors, which were separated by 9 m from each other, each on its own tripod, in order to limit contamination of the turbulence measurements by adjacent structures as much as possible. Moreover, the high-frequency data from all instruments were treated with the same post-processing algorithm. In this study, we compare the results for various turbulence statistics, which include mean horizontal wind speed, standard deviations of vertical wind velocity and sonic temperature, friction velocity, and the buoyancy flux. Quantitative measures of uncertainty, such as bias and comparability, are derived from these results. We find that biases are generally very small for all sensors and all computed variables, except for the sonic temperature measurements of the two Gill sonic anemometers (HS and R3), confirming a known transducer-temperature dependence of the sonic temperature measurement. The best overall agreement between the different instruments was found for the mean wind speed and the buoyancy flux.

scholarly journals Turbulence Measurements with Dual-Doppler Scanning Lidars

2019 ◽  
Vol 11 (20) ◽  
pp. 2444 ◽  
Author(s):  
Alfredo Peña ◽  
Jakob Mann
Keyword(s):  
Radial Velocity ◽  
Velocity Component ◽  
Sonic Anemometer ◽  
Velocity Spectrum ◽  
Doppler Lidar ◽  
Lidar System ◽  
Point Mapping ◽  
Sonic Anemometers ◽  
Scanning Geometry ◽  
First Time

Velocity-component variances can be directly computed from lidar measurements using information of the second-order statistics within the lidar probe volume. Specifically, by using the Doppler radial velocity spectrum, one can estimate the unfiltered radial velocity variance. This information is not always available in current lidar campaigns. The velocity-component variances can also be indirectly computed from the reconstructed velocities but they are biased compared to those computed from, e.g., sonic anemometers. Here we show, for the first time, how to estimate such biases for a multi-lidar system and we demonstrate, also for the first time, their dependence on the turbulence characteristics and the lidar beam scanning geometry relative to the wind direction. For a dual-Doppler lidar system, we also show that the indirect method has an advantage compared to the direct one for commonly-used scanning configurations due to the singularity of the system. We demonstrate that our estimates of the radial velocity and velocity-component biases are accurate by analysis of measurements performed over a flat site using a dual-Doppler lidar system, where both lidars stared over a volume close to a sonic anemometer at a height of 100 m. We also show that mapping these biases over a spatial domain helps to plan meteorological campaigns, where multi-lidar systems can potentially be used. Particularly, such maps help the multi-point mapping of wind resources and conditions, which improve the tools needed for wind turbine siting.

scholarly journals Addressing Spatial Variability of Surface-Layer Wind with Long-Range WindScanners

2015 ◽  
Vol 32 (3) ◽  
pp. 518-527 ◽  
Author(s):  
Jacob Berg ◽  
Nikola Vasiljevíc ◽  
Mark Kelly ◽  
Guillaume Lea ◽  
Michael Courtney
Keyword(s):  
Spatial Variability ◽  
Long Range ◽  
Three Dimensional ◽  
Proof Of Concept ◽  
Large Area ◽  
Vertical Velocity Component ◽  
Sonic Anemometers ◽  
Wind Measurements ◽  
The Mean

AbstractThis paper presents an analysis of mean wind measurements from a coordinated system of long-range WindScanners. From individual scan patterns the mean wind field was reconstructed over a large area, and hence it highlights the spatial variability. From comparison with sonic anemometers, the quality of the WindScanner data is high, although the fidelity of the estimated vertical velocity component is significantly limited by the elevation angles of the scanner heads. The system of long-range WindScanners presented in this paper is close to being fully operational, with the pilot study herein serving not only as a proof of concept but also verifying expectations of reliable wind measurements over arbitrary three-dimensional volumes, in future sustained meteorological campaigns.

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

2020 ◽  
Vol 13 (2) ◽  
pp. 969-983 ◽  
Author(s):  
Matthias Mauder ◽  
Michael Eggert ◽  
Christian Gutsmuths ◽  
Stefan Oertel ◽  
Paul Wilhelm ◽  
...  
Keyword(s):  
High Resolution ◽  
Wind Speed ◽  
Friction Velocity ◽  
Sonic Anemometer ◽  
Vertical Wind ◽  
Doppler Lidar ◽  
Flow Distortion ◽  
Sonic Anemometers ◽  
Vertical Wind Speed ◽  
Standard Deviations

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 is inherently free of any flow distortion. This novel remote sensing instrument has otherwise very similar spatial and temporal sampling characteristics to 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 co-spectra. Our results show an agreement of the mean wind velocity measurements and the standard deviations of the vertical wind speed with a comparability of 0.082 and 0.020 m s−1, respectively. Biases for these two quantities were 0.003 and 0.012 m s−1, respectively. Slightly larger differences were observed for friction velocity. Analysis of the corresponding co-spectra showed that the CSAT3B underestimates this quantity systematically by about 3 % on average as a result of co-spectral losses in the frequency range between 0.1 and 5 s−1. We also found that an angle-of-attack-dependent transducer-shadowing correction does not improve the agreement between the CSAT3B and the Physikalisch-Technische Bundesanstalt (PTB) lidar effectively.

scholarly journals Improvement of vertical velocity statistics measured by a Doppler lidar through comparison with sonic anemometer observations

2016 ◽  
Vol 9 (12) ◽  
pp. 5833-5852 ◽  
Author(s):  
Timothy A. Bonin ◽  
Jennifer F. Newman ◽  
Petra M. Klein ◽  
Phillip B. Chilson ◽  
Sonia Wharton
Keyword(s):  
Vertical Velocity ◽  
Close Agreement ◽  
Sonic Anemometer ◽  
Lag Time ◽  
Volume Averaging ◽  
Doppler Lidar ◽  
Established Method ◽  
Velocity Statistics ◽  
Sonic Anemometers ◽  
Velocity Variance

Abstract. Since turbulence measurements from Doppler lidars are being increasingly used within wind energy and boundary-layer meteorology, it is important to assess and improve the accuracy of these observations. While turbulent quantities are measured by Doppler lidars in several different ways, the simplest and most frequently used statistic is vertical velocity variance (w′2) from zenith stares. However, the competing effects of signal noise and resolution volume limitations, which respectively increase and decrease w′2, reduce the accuracy of these measurements. Herein, an established method that utilises the autocovariance of the signal to remove noise is evaluated and its skill in correcting for volume-averaging effects in the calculation of w′2 is also assessed. Additionally, this autocovariance technique is further refined by defining the amount of lag time to use for the most accurate estimates of w′2. Through comparison of observations from two Doppler lidars and sonic anemometers on a 300 m tower, the autocovariance technique is shown to generally improve estimates of w′2. After the autocovariance technique is applied, values of w′2 from the Doppler lidars are generally in close agreement (R2 ≈ 0.95 − 0.98) with those calculated from sonic anemometer measurements.

scholarly journals Characteristics of Energy Dissipation Rate Observed from the High-Frequency Sonic Anemometer at Boseong, South Korea

Atmosphere ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 837
Author(s):  
Jeonghoe Kim ◽  
Jung-Hoon Kim ◽  
Robert D. Sharman
Keyword(s):  
South Korea ◽  
High Frequency ◽  
Dissipation Rate ◽  
Sonic Anemometer ◽  
Atmospheric Stability ◽  
Turbulence Theory ◽  
Estimation Methods ◽  
The Third ◽  
Sonic Anemometers ◽  
Meteorological Observatory

The characteristics of low-level turbulence at Boseong, located on the southern coast of South Korea, were investigated in terms of eddy dissipation rate (EDR) using 1-year (2018) of wind data obtained from the Boseong Meteorological Observatory (BMO), a World Meteorological Organization testbed. At BMO, a 307 m tall tower is installed on which four high-frequency (20 Hz) sonic anemometers are mounted at 60, 140, and 300 m above ground level (AGL). In addition, a sonic anemometer at 2.5 m AGL is located to the south of the tower. EDRs are estimated from the wind measurements based on three different EDR estimation methods. The first two methods use the inertial dissipation method derived from Kolmogorov turbulence theory, and the third uses a maximum likelihood estimation assuming a von Kármán spectral model. Reasonable agreement was obtained between the three methods with various fluctuations, including diurnal variations for all seasons, while the EDR calculated from the third method displayed slightly higher EDR values than the other two methods. The result of the analysis showed that the mean (standard deviations) of logarithms of EDR had larger values as height decreased (increased), and the means were higher in the unstable planetary boundary layer (PBL) than in the stable PBL for this heterogeneous location adjacent to the coastlines. The probability density functions (PDFs) of the EDRs showed that the distribution was well-represented by a lognormal distribution in both the stable and unstable PBL, although the PDFs at the lowest level (2.5 m) deviated from those at other levels due to surface effects. Seasonal variations in the PDFs showed that there was less difference in the shape of the PDFs depending on atmospheric stability in the wintertime. Finally, we calculate the 1-yr statistics of the observed EDR, which will be used for future LLT forecast systems in Korea.

On the vertical velocity component in the mesoscale Lofoten vortex of the Norwegian Sea

2017 ◽  
Vol 53 (6) ◽  
pp. 641-649 ◽  
Author(s):  
T. V. Belonenko ◽  
I. L. Bashmachnikov ◽  
A. V. Koldunov ◽  
P. A. Kuibin
Keyword(s):  
Vertical Velocity ◽  
Velocity Component ◽  
Vertical Velocity Component ◽  
Norwegian Sea
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