ASTM D5527-00(2011)
(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. These practices apply 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 these practices apply to orthogonal arrays. References are also provided for common types of non-orthogonal arrays.
SCOPE
1.1 These practices cover 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. These practices apply to the measurement of wind velocity components over horizontal terrain using instruments mounted on stationary towers. These practices also apply to speed of sound measurements that are converted to sonic temperatures but do 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 2011)
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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 These practices cover procedures for measuring one-,
3.1 Definitions—Refer to Terminology 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 (6α, deg)— the angular distance,
surement technique.These practices apply 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-
instrumentsmountedonstationarytowers.Thesepracticesalso
biguously defined, and (b) flow across the transducers is
apply to speed of sound measurements that are converted to
unobstructed or remains within the angular range for which
sonic temperatures but do 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)—the record length or time interval
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-
bility of regulatory limitations prior to use.
3.2.5 sonic anemometer/thermometer—an instrument con-
sisting of a transducer array containing paired sets of acoustic
2. Referenced Documents
transmitters and receivers, a system clock, and microprocessor
2.1 ASTM Standards:
circuitrytomeasureintervalsoftimebetweentransmissionand
D1356Terminology Relating to Sampling and Analysis of
reception of sound pulses.
Atmospheres
3.2.5.1 Discussion—The fundamental measurement unit is
D3631Test Methods for Measuring Surface Atmospheric
transittime.Withtransittimeandaknownacousticpathlength,
Pressure
velocity or speed of sound, or both, can be calculated.
D4230Test Method of Measuring Humidity with Cooled-
Instrument output is a series of quasi-instantaneous velocity
Surface Condensation (Dew-Point) Hygrometer
componentreadingsalongeachaxisorspeedofsound,orboth.
E337Test Method for Measuring Humidity with a Psy-
The speed of sound and velocity components may be used to
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
compute sonic temperature (T ), to describe the mean wind
s
peratures)
field, or to compute fluxes, variances, and turbulence intensi-
IEEE/ASTM SI-10American National Standard for Use of
ties.
theInternationalSystemofUnits(SI):TheModernMetric
3.2.6 sonic temperature (T ), (K))— an equivalent tempera-
s
System
ture that accounts for the effects of temperature and moisture
on acoustic wavefront propagation through the atmosphere.
These practices are under the jurisdiction of ASTM Committee D22 on Air
3.2.6.1 Discussion—Sonic temperature is related to the
Quality and are the direct responsibility of Subcommittee D22.11 on Meteorology.
velocity of sound c, absolute temperature T, vapor pressure of
Current edition approved Oct. 1, 2011. Published October 2011. Originally
water e, and absolute pressure P by (1).
approved in 1994. Last previous edition approved in 2007 as D5527–00 (2007).
DOI: 10.1520/D5527-00R11.
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. these practices.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5527 − 00 (2011)
c 5 403T 110.32e/P 5 403T (1) 4.4 For the sonic thermometer, the speed of sound solution
~ !
s
is obtained and converted to a sonic temperature.
(Guidance concerning measurement of P and e are con-
4.5 Variances, covariances, and turbulence intensities are
tained in Test Methods D3631, D4230, and E337.)
computed.
3.2.7 transducer shadow correction—the ratio of the true
along-axisvelocity,asmeasuredinawindtunnelorbyanother
5. Significance and Use
accepted method, to the instrument along-axis wind measure-
ment. 5.1 Sonic anemometer/thermometers are used to measure
3.2.7.1 Discussion—This ratio is used to compensate for turbulent components of the atmosphere except for confined
effects of along-axis flow shadowing by the transducers and areasandveryclosetotheground.Thesepracticesapplytothe
their supporting structure. use of these instruments for field measurement of the wind,
sonic temperature, and atmospheric turbulence components.
3.2.8 transit time (t, (s))—the time required for an acoustic
Thequasi-instantaneousvelocitycomponentmeasurementsare
wavefront to travel from the transducer of origin to the
averaged over user-selected sampling times to define mean
receiving transducer.
along-axis wind components, mean wind speed and direction,
3.3 Symbols:
and the variances or covariances, or both, of individual
B (dimensionless) squared sums of sines and cosines of wind direction
componentsorcomponentcombinations.Covariancesareused
angle used to calculate wind direction standard
for eddy correlation studies and for computation of boundary
deviation
c (m/s) speed of sound layer heat and momentum fluxes. The sonic anemometer/
d (m) acoustic pathlength
thermometerprovidesthedatarequiredtocharacterizethestate
e (Pa) vapor pressure of water
of the turbulent atmospheric boundary layer.
f (dimensionless) compressibility factor
P (Pa) ambient pressure
5.2 The sonic anemometer/thermometer array shall have a
t (s) transit time
sufficiently high structural rigidity and a sufficiently low
T (K) absolute temperature, K
T (K) sonic temperature, K
s coefficient of thermal expansion to maintain an internal align-
γ (dimensionless) specific heat ratio (c /c )
p v
ment to within 60.1°. System electronics must remain stable
M (g/mol) molar mass of air
over its operating temperature range; the time counter oscilla-
n (dimensionless) sample size
R* (J/mol·K) the universal gas constant
tor instability must not exceed 0.01% of frequency. Consult
u (m/s) velocity component along the determined mean wind
with the manufacturer for an internal alignment verification
direction
procedure.
u (m/s) velocity component along the array u axis
s
v (m/s) velocity component crosswind to the determined mean
5.3 The calculations and transformations provided in these
wind direction
v (m/s) velocity component along the array v axis practices apply to orthogonal arrays. References are also
s
w (m/s) vertical velocity
provided for common types of non-orthogonal arrays.
WS (m/s) scalar wind speed computed from measured velocity
components in the horizontal plane
θ (deg) determined mean wind direction with respect to true
6. Interferences
north
θ (deg) wind direction measured in degrees clockwise from the 6.1 Mount the sonic anemometer probe for an acceptance
r
sonic anemometer + v axis to the along-wind u axis
s
angle into the mean wind. Wind velocity components from
α (deg) acceptance angle
angles outside the acceptance angle may be subject to uncom-
φ (deg) orientation of the sonic anemometer axis with respect to
the true north pensated flow blockage effects from the transducers and
σ (deg) standard deviation of wind azimuth angle
θ
supporting structure, or may not be unambiguously defined.
3.4 Units—Units of measurement used should be in accor- Obtain acceptance angle information from the manufacturer.
dance with Practice IEEE/ASTM SI-10.
6.2 Mount the sonic array at a distance that exceeds the
acoustic pathlength by a factor of at least 2π from any
4. Summary of Practice
reflecting surface.
4.1 Acalibratedsonicanemometer/thermometerisinstalled,
6.3 To obtain representative samples of the mean wind, the
leveled,andorientedintotheexpectedwinddirectiontoensure
sonic array must be exposed at a representative site. Sonic
that the measured along-axis velocity components fall within
anemometer/thermometers are typically mounted over level,
the instrument’s acceptance angle.
open terrain at a height of 10 m above the ground. Consider
4.2 The wind components measured over a user-defined
surface roughness and obstacles that might cause flow block-
sampling period are averaged and subjected to a software
age or biases in the site selection process.
rotationintothemeanwind.Thisrotationmaximizesthemean
6.4 Carefully measure and verify array tilt angle and align-
along-axis wind component and reduces the mean cross-
ment. The vertical component of the wind is usually much
component v to zero.
smallerthanthehorizontalcomponents.Therefore,thevertical
4.3 Meanhorizontalwindspeedanddirectionarecomputed
wind component is highly susceptible to cross-component
from the rotated wind components.
contamination from tilt angles not aligned to the chosen
coordinate system. A typical coordinate system may include
establishingalevelwithreferencetoeithertheearthortolocal
Excerpts from IEEE/ASTM SI-10 are included in Vol 11.07. terrain slope. Momentum flux computations are particularly
D5527 − 00 (2011)
susceptible to off-axis contamination (2). Calculations and 8.4 Install cabling to the recording device, and keep cabling
transformations (Section 9) for sonic anemometer data are isolatedfromotherelectronicsnoisesourcesorpowercablesto
based on the assumption that the mean vertical velocity w¯ is minimize induction or crosstalk.
~ !
not significantly different from zero. Arrays mounted above a
8.5 As a system check, collect data for several sequential
sloping surface may require tilt angle adjustments.Also, avoid
sampling periods (of at least 10-min duration over a period of
mounting the array close (within 2 m) to the ground surface
at least 1 h) during representative operating conditions. Exam-
where velocity gradients are large and w¯ may be nonzero.
inedatasamplesforextraneousspikes,noise,alignmentfaults,
6.5 Thetransducersaretinymicrophonesandare,therefore, or other malfunctions. Construct summary statistics for each
sensitive to extraneous noise sources, especially ultrasonic sampling period to include means, variances, and covariances;
sources at the anemometer’s operating frequency. Mount the examine these statistics for reasonableness. Compute 1-h
transducer array in an environment free of extraneous noise spectra and examine for spikes or aliasing affecting the−5⁄3
sources. spectral slope in the inertial subrange.
6.6 Sonic anemometer/thermometer transducer arrays con-
NOTE 2—Calculations and transformations presented in these practices
tribute a certain degree of blockage to flow. Consequently, the are based on the assumption of a zero mean vertical velocity component.
Deviation of the mean vertical velocity component from zero should not
manufacturer should include transducer shadow corrections as
exceed the desired measurement precision. Alignment or data reduction
part of the instrument’s data processing algorithms, or define
softwaremodificationsnotaddressedinthesepracticesmaybeneededfor
an acceptance angle beyond which valid measurements cannot
locations where w is nonzero.
be made, or both.
8.6 Recalibrate and check instrument alignment at least
6.7 Ensurethattheinstrumentisoperatedwithinitsvelocity
once a week, whenever the instrument is subjected to a
calibrationrangeandattemperatureswherethermalsensitivity
significant change in weather conditions, or when transducers
effects are not observed.
or electronics components are changed or adjusted.
6.8 Thesepracticesdonotaddressapplicationswheremois-
8.7 Checkforbias,especiallyinw,usingadatasetcollected
ture is likely to accumulate on the transducers. Moisture
over an extended time period. The array support structure,
accumulationmayinterrupttransmissionoftheacousticsignal,
topography, and changes in ambient temperature may produce
or possibly damage unsealed transducers. Consult the manu-
biases in vertical velocity w. Procedures described in (3) are
facturer concerning operation in adverse environments.
recommended for bias compensation. (Warning—
Uncompensated flow distortion due to the acoustic array and
7. Sampling
supporting structure is possible when the vertical angle of the
7.1 Thebasicsamplingrateofasonicanemometerisonthe
approaching wind exceeds 615°.)
order of several hundred hertz. Transit times are averaged
within the instrument’s software to produce basic measure-
9. Calculations and Transformations
ments at a rate of 10 to 20 Hz, which may be user-selectable.
9.1 Each sonic anemometer provides wind component mea-
This sampling is done to improve instrument measurement
surements with respect to a coordinate system defined by its
precision and to suppress high frequency noise and aliasing
array axis alignment. Each array design requires specific
effects. The 10 to 20-Hz sample output in a serial digital data
calculations and transformations to convert along-axis mea-
stream or through a digital to analog converter is the basic unit
surements to the desired wind component data. The calcula-
of measurement for a sonic anemometer.
tions and transformations are applicable to orthogonal arrays.
7.2 Select a sampling period of sufficient duration to obtain
References (4), (5), and (6) provide information on common
statistically stable measurements of the phenomena of interest.
non-orthogonal arrays. Obtain specific calculations and trans-
Sampling periods of at least 10 min duration usually generate
formation equations from the manufacturer.
sufficient data to describe the turbulent state of the atmosphere
9.2 Fig. 1 illustrates a coordinate system applicable to
during steady wind conditions. Sampling periods in excess of
orthogonal array sonic anemometers. The usual wind compo-
1 h may contain undesired trends in wind direction.
nent sign convention is as follows:
9.2.1 An along-
...
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