共查询到20条相似文献，搜索用时 31 毫秒
1.
Sonic Anemometer Tilt Correction Algorithms 总被引：72，自引：38，他引：72
The sensitivity of sonic anemometer-derived stress estimates to the tilt of the anemometer is investigated. The largest stress errors are shown to occur for unstable stratification (z/L<0) and deep convective boundary layers. Three methods for determining the tilt angles relative to a mean streamline coordinate system and for computing the tilt-corrected stresses are then compared. The most commonly used method, involving a double rotation of the anemometers' axes, is shown to result in significant run-to-run stress errors due to the sampling uncertainty of the mean vertical velocity. An alternative method, requiring a triple rotation of the anemometer axes, is shown to result in even greater run-to-run stress errors due to the combined sampling errors of the mean vertical velocity and the cross-wind stress. For measurements over the sea where the cross-stream stress is important, the double rotation method is shown to overestimate the surface stress, due to the uncorrected lateral tilt component. A third method, using a planar fit technique, isshown to reduce the run-to-run stress errors due to sampling effects, and provides an unbiased estimate of the lateral stress. 相似文献
2.
Hyun-Mi Oh Kyung-Ja Ha Ki-Young Heo Kyung-Eak Kim Sang-Jong Park Jae-Seol Shim Larry Mahrt 《Asia-Pacific Journal of Atmospheric Sciences》2010,46(4):513-523
This study presents an evaluation of the atmospheric factors influencing the post-processing for fast-response data of horizontal momentum, vertical wind component, temperature, and water vapor to measure turbulent fluxes. They are observed at the Ieodo ocean research station over the Yellow Sea during the period of October 2004 to February 2008. The post process methods employed here are composed of quality control and tilt correction for turbulent flux measurement. The present result of quality control on the fast-response data shows that total removal ratio of the data generally depends on the factors such as a wind speed, relative humidity, significant wave height, visibility, and stability parameter (z/L). Especially, the removal ratio of water vapor data is significantly increased on light wind and strong stability conditions. The results show that the total removal ratio of water vapor data increases when wind speed is less than 3 m s?1 and wave height is less than 1 m. The total removal ratio of water vapor data also increases with the value of the stability parameter. Three different algorithms of tilt correction methods (double rotation, triple rotation, and planar fit) are applied to correct the tilt of the sonic anemometer used in the observation. Friction velocities in near neutral state are greater than friction velocity in other states. Drag coefficients are categorized in terms of stabilities and seasons. 相似文献
3.
LIU Li WANG Tijian SUN Zhenhai WANG Qingeng ZHUANG Bingliang HAN Yong LI Shu 《大气科学进展》2012,29(6):1264-1278
Turbulence characteristics of an atmospheric surface layer over a coastal mountain area were investigated under different coordinate frames.Performances of three methods of coordinate rotation:double rotation(DR),triple rotation(TR),and classic planar-fit rotation(PF) were examined in terms of correction of eddy covariance flux.Using the commonly used DR and TR methods,unreasonable rotation angles are encountered at low wind speeds and cause significant run-to-run errors of some turbulence characteristics.The PF method rotates the coordinate system to an ensemble-averaged plane,and shows large tilt error due to an inaccurate fit plane over variable terrain slopes.In this paper,we propose another coordinate rotation scheme.The observational data were separated into two groups according to wind direction.The PF method was adapted to find an ensemble-averaged streamline plane for each group of hourly runs with wind speed exceeding 1.0 m s 1.Then,the coordinate systems were rotated to their respective bestfit planes for all available hourly observations.We call this the PF10 method.The implications of tilt corrections for the turbulence characteristics are discussed with a focus on integral turbulence characteristics,the spectra of wind-velocity components,and sensible heat and momentum fluxes under various atmospheric stabilities.Our results show that the adapted application of PF provides greatly improved estimates of integral turbulence characteristics in complex terrain and maintains data quality.The comparisons of the sensible heat fluxes for four coordinate rotation methods to fluxes before correction indicate that the PF10 scheme is the best to preserve consistency between fluxes. 相似文献
4.
Tilt corrections over complex terrain and their implication for CO<Subscript>2</Subscript> transport
Jielun Sun 《Boundary-Layer Meteorology》2007,124(2):143-159
Observational data from sonic anemometers are commonly rotated from sonic to streamline coordinates, a procedure that is called
tilt correction. Tilt corrections are often used to post-process air velocity data collected from sonic anemometers to allow
objective interpretation of air flow data relative to the Earth. Since streamline coordinates depend on dynamical characteristics
of the flow, the tilt correction depends not only on temporal and spatial variations of the flow, but also on local circulations.
We found that ensemble- averaged slope flows are approximately parallel to the terrain slope close to the ground within the
canopy layer, but not above, due to the influence of the diurnal variation of local vertical circulations. As a result, the
diurnal variation of the observed vertical velocity in streamline coordinates at 21.5 m above the ground over 11-m tall forest
canopies can be opposite to that calculated from the continuity equation. To estimate CO2 transport over sloping terrain, a workable reference coordinate system is needed such that multiple sonic anemometers have
a common reference relative to the Earth. Streamline coordinate systems can be the choice of the common reference coordinate
system only if flow, at least ensemble-averaged flow, is parallel to terrain slopes. The choice of the reference coordinate
system and its implication in investigation of CO2 transport are discussed.
The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
5.
Flow distortion by supporting structures 总被引：3，自引：0，他引：3
A. J. Dyer 《Boundary-Layer Meteorology》1981,20(2):243-251
During the 1976 International Turbulence Comparison Experiment, a number of participants found significant values of upflow over the horizontal support arm of the sensor used. For example, the Japanese sonic anemometer reported an average upflow of 2.4 °. By means of model experiments and fitting to a potential flow solution, it is predicted that the horizontal support would introduce an upflow of 0.5 °. Further model experiments with a full sonic anemometer model plus associated structures predicted an upflow of 2.2 °, in reasonable agreement with the observed result. The need for extreme care in the exposure of turbulence sensors is emphasized. The theory is capable of predicting the error incurred in the various turbulence parameters, such as uw, and these error equations bear a close similarity to those normally used in applying a tilt correction. 相似文献
6.
坐标旋转是涡动协方差(EC)通量观测数据后处理当中必须进行的步骤,本文利用塔克拉玛干沙漠腹地塔中西面标校站自然沙丘上3 m高度和塔中本站32 m高度2009年4—10月湍流通量数据,对比分析了不同坐标旋转方法在塔中通量观测数据中的应用。结果表明,塔克拉玛干沙漠腹地塔中湍流各通量在旋转订正前后差别不显著,不订正造成的通量计算误差1%。塔中32 m和塔中西站3 m通量计算误差,与两个站点的采集仪器架设高度差别较大有关。即使对于相对平坦的下垫面,也必须要进行倾斜校正,以修正地势、仪器振动、安装倾斜等产生的虚假信息。本研究对塔中涡动资料进行旋转时采用了二次坐标旋转方法。此结果为塔克拉玛干沙漠腹地EC通量观测的风速仪倾斜校正提供参考。 相似文献
7.
How Well Can We Measure the Vertical Wind Speed? Implications for Fluxes of Energy and Mass 总被引：2，自引：2，他引：0
John Kochendorfer Tilden P. Meyers John Frank William J. Massman Mark W. Heuer 《Boundary-Layer Meteorology》2012,145(2):383-398
Sonic anemometers are capable of measuring the wind speed in all three dimensions at high frequencies (10–50 Hz), and are relied upon to estimate eddy-covariance-based fluxes of mass and energy over a wide variety of surfaces and ecosystems. In this study, wind-velocity measurement errors from a three-dimensional sonic anemometer with a non-orthogonal transducer orientation were estimated for over 100 combinations of angle-of-attack and wind direction using a novel technique to measure the true angle-of-attack and wind speed within the turbulent atmospheric surface layer. Corrections to the vertical wind speed varied from −5 to 37% for all angles-of-attack and wind directions examined. When applied to eddy-covariance data from three NOAA flux sites, the wind-velocity corrections increased the magnitude of CO2 fluxes, sensible heat fluxes, and latent heat fluxes by ≈11%, with the actual magnitude of flux corrections dependent upon sonic anemometer, surface type, and scalar. A sonic anemometer that uses vertically aligned transducers to measure the vertical wind speed was also tested at four angles-of-attack, and corrections to the vertical wind speed measured using this anemometer were within ±1% of zero. Sensible heat fluxes over a forest canopy measured using this anemometer were 15% greater than sensible heat fluxes measured using a sonic anemometer with a non-orthogonal transducer orientation. These results indicate that sensors with a non-orthogonal transducer orientation, which includes the majority of the research-grade three-dimensional sonic anemometers currently in use, should be redesigned to minimize sine errors by measuring the vertical wind speed using one pair of vertically aligned transducers. 相似文献
8.
Eddy Covariance Measurements On Mountain Slopes: The Advantage Of Surface-Normal Sensor Orientation Over A Vertical Set-Up 总被引：1，自引：1，他引：0
The measurement of scalar fluxes employing the eddy covariance method is a widely used experimental approach,for which the flow distortion due to obstacles (e.g., sensor mounts and mast)is a well-known but not fully solved problem. In order to reduce flow distortion we installed a sonic anemometer in a surface-normal orientationrelative to the terrain slope, and a second instrument in a verticalposition at a horizontal distance of 1.54 m from the first instrumentWe found a significant reduction in the rotation angle necessary for the coordinaterotation procedure in the x-z plane whencomputing 30-minute flux averages with the surface-normal orientation. In 91% of all cases this rotation angleremained within the angle of incidence of ±10° recommended bythe manufacturer. In contrast, only 24% of the measurements taken with the vertically mounted anemometer were obtained at an angle of incidencewithin ±10°, and 3% were outside the ±30° range specified for an acceptable operation.A data quality test based on the variance of vertical windspeed normalized with friction velocity (w/u*) revealed problems for application under stable conditions due to large uncertainties in the determination of the Monin–Obukhov stability parameter z/L. An alternative test using the bulk drag coefficient CD revealed other problems related to the dependence of CD on z/z0, the measuring height normalized by the roughness length, which do not appear to be constantin complex terrain. With both tests, a tendency for a slightly improved dataquality was found for the surface normal set-up, which, however, proved statistically insignificant.It is concluded that the surface-normal set-up of a sonic anemometer significantly reduces flow distortion by thesensor head. Although the surface-normal mounting position therefore appears to be the preferred one, with decreased flow distortion and a slightly improved data quality, no significant differences in turbulent quantities were found between the two set-uppositions. Hence, the consequences for short-term measurements of massand energy fluxes with a surface-normal set-up in complex terrain appearto be relevant only if single flux events are to be inspected, while for long-term measurements of integrated fluxes both the surface-normaland vertical installation of the sonic anemometer are adequate,indicating that eddy covariance measurements in complex terrain are lessdelicate than expected. 相似文献
9.
该文基于对风杯风速仪动力方程的数值计算和风杯风速仪与超声风速仪平行对比的观测结果,发现专用于近地面层精细风廓线测量的轻型低阈值风杯风速仪测风的过高效应引起的u-error约为1%,因风速平均方法不同（标量平均和矢量平均）引起的DP-error是风杯风速仪测风过高的主要原因,在小风情况下更为明显。DP-error经修正后可获得合理的风速值。 相似文献
10.
This paper investigates processing of fast-response data and corrections of turbulent fluxes obtained by using eddy covariance method based on data collected at an offshore observation tower during three Cold-intrusion(CI)events in the South China Sea in 2010. This study presents the data processing procedure in detail and compares frictional velocities(u*), sensible heat fluxes(H) and latent heat fluxes(LE) yielded by using different averaging periods and different coordinate rotation methods; evaluates the sonic temperature correction for sensible heat flux and the Webb correction for latent heat flux as a function of 10 m wind speed(u10) during the CIs. The results show(1) that the different averaging periods of 30 min and 10 min cause biases of u*(H, LE) within 5%(15%, 62%). The values of u*(H,LE) averaged from 30 mins are mostly larger than those averaged from 10 mins. We suggest that the averaging period of 10 min is not sufficiently long to capture all scale eddies and recommend 30 min averaging period in calculating turbulent fluxes using eddy covariance method during CIs;(2) that the values of u*(H, LE) obtained from double rotation(DR2) and those obtained from planar fit rotation(PF) have good agreements and correlation coefficients between them are larger than 0.99. Because PF method requires unchanged environment and it is easier to apply DR2 method, we suggest DR2 coordinate rotation method in processing fast-response data; and(3) that the median values of frictional velocity(sensible heat flux and latent heat flux) binned according to 2 m s~(-1) intervals of u_(10) increase(decrease,increase) by less than 9%(4%, 10%) by Coriolis corrections(sonic temperature corrections, Webb corrections), which decreases(decreases, increases) with increasing u10 when u10 are 5-17 m s~(-1). 相似文献
11.
12.
An anemometer based upon measurement of the tangential windspeed around a sphere with hot-film probes is described. The anemometer determined the windspeed with a root-mean-square (rms) error of 5%, and the direction with an rms error of 5.6 °. A comparison between omnidirectional and sonic anemometers in the field gave practically identical results for the vertical sensible heat flux using eddy correlation procedures. Other turbulence statistics are also reported. The new instrument should be useful for measurements in canopies, where turbulence intensities are often large. 相似文献
13.
A. E. Green M. J. Judd J. K. McAneney M. S. Astill P. T. Prendergast 《Boundary-Layer Meteorology》1991,57(1-2):1-15
A rapid response drag anemometer for measuring streamwise and lateral components of horizontal windspeed is described. Theory of operation, design and calibration are discussed with emphasis on the electronic preconditioning of signals and problems associated with using a mechanically resonant system as a sensor. Field comparisons showed half-hourly means and standard deviations of the streamwise component to be within 8% and 5% of respective values obtained from a 3-dimensional sonic anemometer. The lateral component from the drag anemometer was significantly more noisy than that from the 3-D sonic due to induced oscillations arising from vortex shedding. After mechanical and electronic filtering, half-hourly standard deviation comparisons agreed to within 6% for this component. Friction velocities obtained from the drag anemometer in combination with a 1-D sonic, agreed with measurements from the 3-D sonic anemometer to within 4% over a measured range of 0.05 to 1.2 m s-1 相似文献
14.
Renmin Yuan Minseok Kang Sung-Bin Park Jinkyu Hong Dongho Lee Joon Kim 《Meteorology and Atmospheric Physics》2011,110(3-4):123-133
An expanded planar-fit (PF) method over complex terrain is presented and applied to coordinate rotation of the eddy-covariance (EC) flux and vertical velocity estimation. Theoretical analysis indicates that PF coefficients depend on wind direction, and an expression of vertical velocity is deduced. We applied the theory using 1?year of observations from the KoFlux site in the Gwangneung Forest in Korea and investigated the influence of wind direction on the PF method. Then, we performed an expansion of the PF method to consider dependence of PF coefficients on wind direction and applied the PF method to every sector. The results show that the PF coefficients and tilt angles over complex terrain vary with wind direction. Two hundred 30-min data sets are sufficient to derive stable PF coefficients over hilly terrain for each sector. The relative difference in eddy-covariance flux between the general planar fit (GPF) and sector planar fit (SPF) is less than 10% for the scalar flux and about 18% for friction velocity. Vertical velocity and vertical advection (VA) terms were also calculated and compared using SPF and GPF methods, and a normal distribution and diurnal trend of real vertical velocity on clear days are presented. 相似文献
15.
Sergey N. Vecherin Vladimir E. Ostashev Christopher W. Fairall D. Keith Wilson Ludovic Bariteau 《Boundary-Layer Meteorology》2013,149(2):165-178
The spatial resolution of a sonic anemometer is limited by the distance between its transducers, and for studies of small-scale turbulence and theories of turbulence, it is desirable to increase this spatial resolution. We here consider resolution improvements obtainable by treating the sonic anemometer as a small tomography array, with application of appropriate inverse algorithms for the reconstruction of temperature and velocity. A particular modification of the sonic anemometer is considered when the number of its transducers is doubled and the time-dependent stochastic inversion algorithm is used for reconstruction. Numerical simulations of the sonic anemometer and its suggested modification are implemented with the temperature and velocity fields modelled as discrete eddies moving through the sonic’s volume. The tomographic approach is shown to provide better reconstructions of the temperature and velocity fields, with spatial resolution increased by as much as a factor of ten. The spatial resolution depends on the inverse algorithm and also improves by increasing the number of transducers. 相似文献
16.
M. G. Mennen H. J. M. A. Zwart J. E. M. Hogenkamp J. W. Erisman 《Boundary-Layer Meteorology》1996,81(3-4):353-371
Flow distortion errors on wind and friction velocity induced by a box simulating the housing of a gas analyzer used in dry
deposition eddy correlation measurements were determined in a field experiment. ‘Undisturbed’ and ‘disturbed’ wind and friction
velocities, measured with two dry deposition monitoring systems run simultaneously, were compared, one to the other. In the
‘disturbed’ case the box was mounted below the 3-component probe of the sonic anemometer of one of these systems, while in
the ‘undisturbed’ case the box was removed. When the probe was located on the upstream side of the box, the results showed
satisfactory agreement with theoretical estimates using Wyngaard’s potential-flow approach and a spherical model for the box.
This model can be applied to obtain first-order corrections for flow distortion errors induced by cubic-like (or spherical)
obstacles such as a gas analyzer housing used in dry deposition research systems, or to determine the optimal location of
this housing relative to the sonic probe in such systems. When the probe was located halfway downstream and halfway to the
side of the box, the experimental flow distortion errors did not exceed those for the upstream case. This implies that to
keep flow distortion errors in dry deposition systems as small as possible the sonic probe can be placed upstream but also
to the side of the gas analyzer housing. The results of our experiments also confirmed that correcting for flow distortion
with the commonly used tilt equations yields underestimated values. 相似文献
17.
Errors in turbulence measurements with a sonic anemometer 总被引：1，自引：0，他引：1
Errors in surface-layer wind data obtained by sonic anemometers are estimated as a function of relative wind direction using a comparison between two identical anemometers. The maximum errors in mean windspeed and the standard deviations of the horizontal wind components are found to be between 10 and 20%. Agreement between the size of the measured errors and those calculated from wind-tunnel data is fair.In addition, vertical velocity data are analysed to show the presence of flow distortion induced by the asymmetry in the sonic anemometer probe and the mounting of the probe on the top of a mast. 相似文献
18.
The Campbell CSAT3 sonic anemometer is one of the most popular instruments for turbulence measurements in basic micrometeorological research and ecological applications. While measurement uncertainty has been characterized by field experiments and wind-tunnel studies in the past, there are conflicting estimates, which motivated us to conduct a numerical experiment using large-eddy simulation to evaluate the probe-induced flow distortion of the CSAT3 anemometer under controlled conditions, and with exact knowledge of the undisturbed flow. As opposed to wind-tunnel studies, we imposed oscillations in both the vertical and horizontal velocity components at the distinct frequencies and amplitudes found in typical turbulence spectra in the surface layer. The resulting flow-distortion errors for the standard deviations of the vertical velocity component range from 3 to 7%, and from 1 to 3% for the horizontal velocity component, depending on the azimuth angle. The magnitude of these errors is almost independent of the frequency of wind speed fluctuations, provided the amplitude is typical for surface-layer turbulence. A comparison of the corrections for transducer shadowing proposed by both Kaimal et al. (Proc Dyn Flow Conf, 551–565, 1978) and Horst et al. (Boundary-Layer Meteorol 155:371–395, 2015) show that both methods compensate for a larger part of the observed error, but do not sufficiently account for the azimuth dependency. Further numerical simulations could be conducted in the future to characterize the flow distortion induced by other existing types of sonic anemometers for the purposes of optimizing their geometry. 相似文献
19.
Atsushi Inagaki Manabu Kanda Shiho Onomura Hideaki Kumemura 《Boundary-Layer Meteorology》2013,149(1):1-18
A method for measuring the two-dimensional distribution of wind velocity vectors near a surface exposed to solar radiation, by tracking brightness temperature images instead of particle images, is proposed. It is based on time-sequential thermography with the algorithm used for particle image velocimetry. This thermal image velocimetry (TIV) was tested on a full-scale building wall covered by polystyrene boards attached side-by-side over a vertically elongated area measuring 22.2 m by 2.73 m. A thermal infrared camera was installed 8 m from the test wall to capture the wall-surface temperature at 30 Hz frequency. A sonic anemometer was also installed 35 mm from the surface used for validation of the TIV. The advection velocity estimated from thermal infrared imagery had a linear relationship with the wind velocity measured by the sonic anemometer, irrespective of the wind speed and direction. This linear slope was multiplied by the advection velocity of the thermal infrared image to rescale it to the wind velocity, and the term ‘TIV velocity’ was then used. A histogram and power spectra of the TIV velocity showed quantitatively good agreement with the velocity measured by the sonic anemometer, except for the high-frequency region of the spectra, where the TIV velocity was overestimated compared with that of the sonic anemometer. The method was also tested on ground covered by artificial turf to demonstrate its application to a horizontal plane with a wider area, extending for more than 80 m by 60 m. 相似文献
20.
Direct measurement of turbulent fluxes on a cruising ship 总被引：1，自引：0，他引：1
The result of an attempt at the direct measurement of turbulent fluxes on the top of the mast of a cruising ship is presented. The three-dimensional components of wind relative to the ship measured by a sonic anemometer are corrected for ship motion; from these the fluxes of momentum, sensible heat and water vapor are computed using the outputs of a fine-wire thermocouple psychrometer. The observations were made by this method on the Northwestern Pacific. The results indicate that this technique is usable for determining the distribution of fluxes over the ocean. 相似文献