All Sonic Anemometers Need to Correct for Transducer and Structural Shadowing in Their Velocity Measurements

Frank, J. M.; Massman, W. J.; Swiatek, E.; Zimmerman, H.; Ewers, B. E.

doi:10.1175/jtech-d-15-0171.1

Cited by 39 publications

(43 citation statements)

References 29 publications

(58 reference statements)

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Obviously, the results of this intercomparison contradict the findings of H15, Frank et al (2016) and Huq et al (2017), who advocate the need of a flow-distortion correction on ′ ′ ̅̅̅̅̅̅1/2 on the order of several percent. However, these previous field intercomparisons only compared two sonic anemometers with each other, perhaps with different sensor geometries, but none of them can be considered as flow-distortion free as the bistatic Doppler lidar that we employed.…”

Section: Spectral and Cospectral Analysiscontrasting

confidence: 78%

“…Particularly, the measurements of the vertical velocity fluctuations are almost identical with a regression slope of 0.989, a correlation coefficient of 0.998 and a comparability of 0.017 m s −1 . This is 10 somewhat unexpected because previous studies indicated an underestimation of ′ ′ ̅̅̅̅̅̅1/2 by 3-5 % due to probe-induced flow distortion (H15, Frank et al, 2016). However, only a very small negative bias of −0.009 m s −1 was found in our analysis using the flow-distortion-free PTB lidar as reference.…”

Section: Comparison Of Turbulence Statisticssupporting

confidence: 60%

“…underestimation of turbulent fluctuations due to probe-induced flow-distortion errors (Frank et al, 2013(Frank et al, , 2016Wyngaard, 1988). These errors can be further classified into errors due to transducer self-shadowing, caused by cross-shadowing and influences of the support structure.…”

mentioning

confidence: 99%

See 2 more Smart Citations

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

Mauder¹,

Eggert²,

Gutsmuths³

et al. 2019

Preprint

View full text Add to dashboard Cite

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.

show abstract

Section: Spectral and Cospectral Analysiscontrasting

confidence: 78%

Section: Comparison Of Turbulence Statisticssupporting

confidence: 60%

See 1 more Smart Citation

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

Mauder¹,

Eggert²,

Gutsmuths³

et al. 2019

Preprint

View full text Add to dashboard Cite

show abstract

“…It appears to be a rather general phenomenon at most EC sites, despite differences in measurement set up and vegetation cover (Foken et al, 2011). The most likely candidates to explain this systematic behaviour are mesoscale flux contributions (Mahrt, 1998;Mauder, Desjardins, & MacPherson, 2007;Eder, Schmidt, Damian, Träumner, & Mauder, 2015) and a potential bias of sonic anemometers commonly used in EC systems (Frank, Massman, Swiatek, Zimmerman, & Ewers, 2016;Horst, Semmer, & Maclean, 2015). Nevertheless, the causes of this problem are still under discussion.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of energy balance closure adjustment methods by independent evapotranspiration estimates from lysimeters and hydrological simulations

Mauder

Genzel

et al. 2017

Hydrological Processes

View full text Add to dashboard Cite

Non‐closure of the surface energy balance is a frequently observed phenomenon of hydrometeorological field measurements, when using the eddy‐covariance method, which can be ascribed to an underestimation of the turbulent fluxes. Several approaches have been proposed in order to adjust the measured fluxes for this apparent systematic error. However, there are uncertainties about partitioning of the energy balance residual between the sensible and latent heat flux and whether such a correction should be applied on 30‐min data or longer time scales. The data for this study originate from two grassland sites in southern Germany, where measurements from weighable lysimeters are available as reference. The adjusted evapotranspiration rates are also compared with joint energy and water balance simulations using a physically based distributed hydrological model. We evaluate two adjustment methods: the first one preserves the Bowen ratio and the correction factor is determined on a daily basis. The second one attributes a smaller portion of the residual energy to the latent heat flux than to the sensible heat flux for closing the energy balance for every 30‐min flux integration interval. Both methods lead to an improved agreement of the eddy‐covariance based fluxes with the independent lysimeter estimates and the physically based model simulations. The first method results in a better comparability of evapotranspiration rates, and the second method leads to a smaller overall bias. These results are similar between both sites despite considerable differences in terrain complexity and grassland management. Moreover, we found that a daily adjustment factor leads to less scatter than a complete partitioning of the residual for every half‐hour time interval. The vertical temperature gradient in the surface layer and friction velocity were identified as important predictors for a potential future parameterisation of the energy balance residual.

show abstract

“…Even in the hypothetical situation of perfectly synchronized timestamps for wind and gas data, if the respective instruments' sampling volumes have to be spatially separated to avoid presently intractable flow distortion issues in the anemometer, as is notably the case with open-path setups (see, for example, Wyngaard, 1988;Frank et al, 2016;Horst et al, 2016;Grare et al, 10 2016 andHuq et al 2017), the corresponding timeseries will be affected by misalignment, possibly to varying degrees.…”

Section: ): 25mentioning

confidence: 99%

Eddy Covariance flux errors due to random and systematic timing errors during data acquisition

Fratini¹,

Sabbatini²,

Ediger³

et al. 2018

Preprint

View full text Add to dashboard Cite

Abstract. Modern Eddy Covariance (EC) systems collect high-frequency data (10-20 Hz) via instruments' digital outputs.While this helps overcome the limits of traditional mixed analog/digital systems, it also introduces the new problem of guaranteeing data synchronicity when the clocks of the involved devices cannot themselves be synchronized, which is often 10 the case with instruments providing data via serial or Ethernet connectivity. By means of a simulation study, we found that in most cases random timing errors can safely be neglected, as they don't impact fluxes to a large extent. On the contrary, realistic systematic timing errors potentially arising in asynchronous systems can lead to flux underestimations as large as 10%, by means of attenuation of high-frequency flux contributions. We characterize the transfer function of such filters as a function of the error amount and find cut-off frequencies as low as 1 Hz, which means that synchronization errors can 15 dominate high-frequency attenuations in open-and enclosed-path EC systems. In most cases, such timing errors cannot be detected nor quantified a posteriori. Therefore, we suggest testing the ability of prospect EC data logging systems to assure required synchronicity and propose a procedure to implement such a test which relies on readily available equipment.

show abstract

All Sonic Anemometers Need to Correct for Transducer and Structural Shadowing in Their Velocity Measurements

Cited by 39 publications

References 29 publications

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

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

Evaluation of energy balance closure adjustment methods by independent evapotranspiration estimates from lysimeters and hydrological simulations

Eddy Covariance flux errors due to random and systematic timing errors during data acquisition

Contact Info

Product

Resources

About