ASTM D5527-00(2002)e1
(Practice)Standard Practices for Measuring Surface Wind and Temperature by Acoustic Means
Standard Practices for Measuring Surface Wind and Temperature by Acoustic Means
SIGNIFICANCE AND USE
Sonic anemometer/thermometers are used to measure turbulent components of the atmosphere except for confined areas and very close to the ground. This practice applies to the use of these instruments for field measurement of the wind, sonic temperature, and atmospheric turbulence components. The quasi-instantaneous velocity component measurements are averaged over user-selected sampling times to define mean along-axis wind components, mean wind speed and direction, and the variances or covariances, or both, of individual components or component combinations. Covariances are used for eddy correlation studies and for computation of boundary layer heat and momentum fluxes. The sonic anemometer/thermometer provides the data required to characterize the state of the turbulent atmospheric boundary layer.
The sonic anemometer/thermometer array shall have a sufficiently high structural rigidity and a sufficiently low coefficient of thermal expansion to maintain an internal alignment to within ±0.1°. System electronics must remain stable over its operating temperature range; the time counter oscillator instability must not exceed 0.01 % of frequency. Consult with the manufacturer for an internal alignment verification procedure.
The calculations and transformations provided in this practice apply to orthogonal arrays. References are also provided for common types of non-orthogonal arrays.
SCOPE
1.1 This practice covers procedures for measuring one-, two-, or three-dimensional vector wind components and sonic temperature by means of commercially available sonic anemometer/thermometers that employ the inverse time measurement technique. This practice applies to the measurement of wind velocity components over horizontal terrain using instruments mounted on stationary towers. This practice also applies to speed of sound measurements that are converted to sonic temperatures but does not apply to the measurement of temperature by the use of ancillary temperature devices.
1.2 The values stated in SI units are to be regarded as the standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D5527–00 (Reapproved 2002)
Standard Practices for
Measuring Surface Wind and Temperature by Acoustic
Means
This standard is issued under the fixed designation D5527; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Made editorial corrections to the table in 3.3 and to Equation 8 in October 2002.
1. Scope 3. Terminology
1.1 This practice covers procedures for measuring one-, 3.1 Definitions—Refer toTerminology D1356 for common
two-, or three-dimensional vector wind components and sonic terminology.
temperature by means of commercially available sonic 3.2 Definitions of Terms Specific to This Standard:
anemometer/thermometers that employ the inverse time mea- 3.2.1 acceptance angle (6a, deg)— the angular distance,
surement technique. This practice applies to the measurement centered on the array axis of symmetry, over which the
of wind velocity components over horizontal terrain using following conditions are met: (a) wind components are unam-
instruments mounted on stationary towers. This practice also biguously defined, and (b) flow across the transducers is
applies to speed of sound measurements that are converted to unobstructed or remains within the angular range for which
sonic temperatures but does not apply to the measurement of transducer shadow corrections are defined.
temperature by the use of ancillary temperature devices. 3.2.2 acoustic pathlength (d, (m))—the distance between
1.2 The values stated in SI units are to be regarded as the transducer transmitter-receiver pairs.
standard. 3.2.3 sampling period(s)—therecordlengthortimeinterval
1.3 This standard does not purport to address all of the over which data collection occurs.
safety concerns, if any, associated with its use. It is the 3.2.4 sampling rate (Hz)—the rate at which data collection
responsibility of the user of this standard to establish appro- occurs, usually presented in samples per second or Hertz.
priate safety and health practices and determine the applica- 3.2.5 sonic anemometer/thermometer—an instrument con-
bility of regulatory limitations prior to use. sisting of a transducer array containing paired sets of acoustic
transmitters and receivers, a system clock, and microprocessor
2. Referenced Documents
circuitrytomeasureintervalsoftimebetweentransmissionand
2.1 ASTM Standards: reception of sound pulses.
D1356 Standard Terminology Relating to Sampling and
3.2.5.1 Discussion—The fundamental measurement unit is
Analysis of Atmospheres transittime.Withtransittimeandaknownacousticpathlength,
D3631 Test Methods for Measuring Surface Atmospheric
velocity or speed of sound, or both, can be calculated.
Pressure Instrument output is a series of quasi-instantaneous velocity
D4230 Test Method of Measuring Humidity with Cooled-
componentreadingsalongeachaxisorspeedofsound,orboth.
Surface Condensation (Dew-Point) Hygrometer The speed of sound and velocity components may be used to
E337 Test Method for Measuring Humidity with a Psy-
compute sonic temperature (T ), to describe the mean wind
s
chrometer (the Measurement of Wet- and Dry-Bulb Tem- field, or to compute fluxes, variances, and turbulence intensi-
peratures)
ties.
E380 Practice for Use of the International System of Units 3.2.6 sonic temperature (T ), (K))— an equivalent tempera-
s
(SI) (the Modernized Metric System)
ture that accounts for the effects of temperature and moisture
on acoustic wavefront propagation through the atmosphere.
3.2.6.1 Discussion—Sonic temperature is related to the
ThispracticeisunderthejurisdictionofASTMCommitteeD22onAirQuality
velocity of sound c, absolute temperature T, vapor pressure of
and is the direct responsibility of Subcommittee D22.11 on Meteorology.
water e, and absolute pressure P by (1).
Current edition approved Oct. 10, 2002. Published November 2000. Originally
published as D5527–94. Last previous edition D5527–94.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
the ASTM website. this practice.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D5527–00 (2002)
4.5 Variances, covariances, and turbulence intensities are
c 5403T ~1 10.32e/P! 5403T (1)
s
computed.
(Guidanceconcerningmeasurementof Pand earecontained
in Test Methods D3631, D4230, and E337.)
5. Significance and Use
3.2.7 transducer shadow correction—the ratio of the true
5.1 Sonic anemometer/thermometers are used to measure
along-axisvelocity,asmeasuredinawindtunnelorbyanother
turbulent components of the atmosphere except for confined
accepted method, to the instrument along-axis wind measure-
areas and very close to the ground.This practice applies to the
ment.
use of these instruments for field measurement of the wind,
3.2.7.1 Discussion—This ratio is used to compensate for
sonic temperature, and atmospheric turbulence components.
effects of along-axis flow shadowing by the transducers and
Thequasi-instantaneousvelocitycomponentmeasurementsare
their supporting structure.
averaged over user-selected sampling times to define mean
3.2.8 transit time (t, (s))—the time required for an acoustic
along-axis wind components, mean wind speed and direction,
wavefront to travel from the transducer of origin to the
and the variances or covariances, or both, of individual
receiving transducer.
componentsorcomponentcombinations.Covariancesareused
3.3 Symbols:
for eddy correlation studies and for computation of boundary
B (dimensionless) squared sums of sines and cosines of wind direction
layer heat and momentum fluxes. The sonic anemometer/
angle used to calculate wind direction standard devia-
tion thermometerprovidesthedatarequiredtocharacterizethestate
c (m/s) speed of sound
of the turbulent atmospheric boundary layer.
d (m) acoustic pathlength
5.2 The sonic anemometer/thermometer array shall have a
e (Pa) vapor pressure of water
f (dimensionless) compressibility factor sufficiently high structural rigidity and a sufficiently low
P (Pa) ambient pressure
coefficient of thermal expansion to maintain an internal align-
t (s) transit time
ment to within 60.1°. System electronics must remain stable
T (K) absolute temperature, K
T (K) sonic temperature, K over its operating temperature range; the time counter oscilla-
s
g (dimensionless) specific heat ratio (c /c )
p v
tor instability must not exceed 0.01% of frequency. Consult
M (g/mol) molar mass of air
with the manufacturer for an internal alignment verification
n (dimensionless) sample size
R* (J/mol·K) the universal gas constant procedure.
u (m/s) velocity component along the determined mean wind di-
5.3 The calculations and transformations provided in this
rection
practice apply to orthogonal arrays. References are also pro-
u (m/s) velocity component along the array u axis
s
v (m/s) velocity component crosswind to the determined mean
vided for common types of non-orthogonal arrays.
wind direction
v (m/s) velocity component along the array v axis
s
6. Interferences
w (m/s) vertical velocity
WS (m/s) scalar wind speed computed from measured velocity 6.1 Mount the sonic anemometer probe for an acceptance
components in the horizontal plane
angle into the mean wind. Wind velocity components from
u (deg) determined mean wind direction with respect to true
angles outside the acceptance angle may be subject to uncom-
north
u (deg) wind direction measured in degrees clockwise from the pensated flow blockage effects from the transducers and
r
sonic anemometer + v axis to the along-wind u axis
s
supporting structure, or may not be unambiguously defined.
a (deg) acceptance angle
Obtain acceptance angle information from the manufacturer.
f (deg) orientation of the sonic anemometer axis with respect to
the true north 6.2 Mount the sonic array at a distance that exceeds the
s (deg) standard deviation of wind azimuth angle
u
acoustic pathlength by a factor of at least 2p from any
reflecting surface.
3.4 Abbreviations:Units—Units of measurement used
should be in accordance with Practice E380. 6.3 To obtain representative samples of the mean wind, the
sonic array must be exposed at a representative site. Sonic
4. Summary of Practice
anemometer/thermometers are typically mounted over level,
open terrain at a height of 10 m above the ground. Consider
4.1 Acalibratedsonicanemometer/thermometerisinstalled,
surface roughness and obstacles that might cause flow block-
leveled,andorientedintotheexpectedwinddirectiontoensure
age or biases in the site selection process.
that the measured along-axis velocity components fall within
6.4 Carefully measure and verify array tilt angle and align-
the instrument’s acceptance angle.
ment. The vertical component of the wind is usually much
4.2 The wind components measured over a user-defined
smallerthanthehorizontalcomponents.Therefore,thevertical
sampling period are averaged and subjected to a software
wind component is highly susceptible to cross-component
rotationintothemeanwind.Thisrotationmaximizesthemean
contamination from tilt angles not aligned to the chosen
along-axis wind component and reduces the mean cross-
coordinate system. A typical coordinate system may include
component v to zero.
establishingalevelwithreferencetoeithertheearthortolocal
4.3 Meanhorizontalwindspeedanddirectionarecomputed
terrain slope. Momentum flux computations are particularly
from the rotated wind components.
susceptible to off-axis contamination (2). Calculations and
4.4 For the sonic thermometer, the speed of sound solution
transformations (Section 9) for sonic anemometer data are
is obtained and converted to a sonic temperature.
basedontheassumptionthatthemeanverticalvelocity( w)is
not significantly different from zero. Arrays mounted above a
Excerpts from Practice E380 are included in Vol 11.03. sloping surface may require tilt angle adjustments.Also, avoid
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D5527–00 (2002)
mounting the array close (within 2 m) to the ground surface or other malfunctions. Construct summary statistics for each
where velocity gradients are large and w may be nonzero. sampling period to include means, variances, and covariances;
6.5 Thetransducersaretinymicrophonesandare,therefore, examine these statistics for reasonableness. Compute 1-h
sensitive to extraneous noise sources, especially ultrasonic spectra and examine for spikes or aliasing affecting the−5/3
sources at the anemometer’s operating frequency. Mount the spectral slope in the inertial subrange.
transducer array in an environment free of extraneous noise
NOTE 2—Calculations and transformations presented in this practice
sources.
are based on the assumption of a zero mean vertical velocity component.
6.6 Sonic anemometer/thermometer transducer arrays con-
Deviation of the mean vertical velocity component from zero should not
tribute a certain degree of blockage to flow. Consequently, the
exceed the desired measurement precision. Alignment or data reduction
manufacturer should include transducer shadow corrections as software modifications not addressed in this practice may be needed for
locations where w is nonzero.
part of the instrument’s data processing algorithms, or define
an acceptance angle beyond which valid measurements cannot
8.6 Recalibrate and check instrument alignment at least
be made, or both.
once a week, whenever the instrument is subjected to a
6.7 Ensurethattheinstrumentisoperatedwithinitsvelocity
significant change in weather conditions, or when transducers
calibrationrangeandattemperatureswherethermalsensitivity
or electronics components are changed or adjusted.
effects are not observed.
8.7 Checkforbias,especiallyin w,usingadatasetcollected
6.8 This practice does not address applications where mois-
over an extended time period. The array support structure,
ture is likely to accumulate on the transducers. Moisture
topography, and changes in ambient temperature may produce
accumulationmayinterrupttransmissionoftheacousticsignal,
biases in vertical velocity w. Procedures described in (3) are
or possibly damage unsealed transducers. Consult the manu-
recommended for bias compensation. (Warning—
facturer concerning operation in adverse environments.
Uncompensated flow distortion due to the acoustic array and
supporting structure is possible when the vertical angle of the
7. Sampling
approaching wind exceeds 615°.)
7.1 Thebasicsamplingrateofasonicanemometerisonthe
order of several hundred hertz. Transit times are averaged
9. Calculations and Transformations
within the instrument’s software to produce basic measure-
9.1 Eachsonicanemometerprovideswindcomponentmea-
ments at a rate of 10 to 20 Hz, which may be user-selectable.
surements with respect to a coordinate system defined by its
This sampling is done to improve instrument measurement
array axis alignment. Each array design requires specific
precision and to suppress high frequency noise and aliasing
calculations and transformations to convert along-axis mea-
effects. The 10 to 20-Hz sample output in a serial digital data
surements to the desired wind component data. The calcula-
streamorthroughadigitaltoanalogconverteristhebasicunit
tions and transformations are applicable to orthogonal arrays.
of measurement for a sonic anemometer.
References (4), (5), and (6) provide information on common
7.2 Select a sampling period of sufficient duration to obtain
non-orthogonal arrays. Obtain specific calculations and trans-
statistically stable measurements of the phenomena of interest.
formation equations from the manufacturer.
Sampling periods of at least 10 min duration usually generate
9.2 Fig. 1 illustrates a coordinate system applicable to
sufficient data to describe the turbulent state of the atmosphere
orthogonal array sonic anemometers. The usual wind compo-
during steady wind conditions. Sampling periods in excess of
nent sign convention is as follows:
1 h may contain undesired trends in wind direction.
9.2.1 An along-axis wind component entering the array
from the front will have a positive sign (+u ).
8. Procedure
si
9.2.2 Across-axis wind component entering the array from
8.1 Perform system calibration in a zero wind chamber
the left will have a positive sign (+v ).
(refer to the manufacturer’s instructions). si
9.2.3 Averticalwindcomponententeringthearrayfromthe
8.2 Mount the instrume
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