ASTM D5527-00(2007)
(Practice)Standard Practices for Measuring Surface Wind and Temperature by Acoustic Means
Standard Practices for Measuring Surface Wind and Temperature by Acoustic Means
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 2007)
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 (6a, 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)—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 Terminology Relating to Sampling and Analysis of
3.2.5.1 Discussion—The fundamental measurement unit is
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.
IEEE/ASTM SI-10 American National Standard for Use of 3.2.6 sonic temperature (T ), (K))— an equivalent tempera-
s
the International System of Units (SI): The Modern Metric
ture that accounts for the effects of temperature and moisture
System on acoustic wavefront propagation through the atmosphere.
3.2.6.1 Discussion—Sonic temperature is related to the
velocity of sound c, absolute temperature T, vapor pressure of
These practices are under the jurisdiction of ASTM Committee D22 on Air
water e, and absolute pressure P by (1).
Quality and are the direct responsibility of Subcommittee D22.11 on Meteorology.
Current edition approved Oct. 1, 2007. Published December 2007. Originally 2
c 5403T ~1 10.32e/P! 5403T (1)
´1 s
approved in 1994. Last previous edition approved in 2002 as D5527-00(2002) .
DOI: 10.1520/D5527-00R07.
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 (2007)
(Guidanceconcerningmeasurementof Pand earecontained 5. Significance and Use
in Test Methods D3631, D4230, and E337.)
5.1 Sonic anemometer/thermometers are used to measure
3.2.7 transducer shadow correction—the ratio of the true
turbulent components of the atmosphere except for confined
along-axisvelocity,asmeasuredinawindtunnelorbyanother
areasandveryclosetotheground.Thesepracticesapplytothe
accepted method, to the instrument along-axis wind measure-
use of these instruments for field measurement of the wind,
ment.
sonic temperature, and atmospheric turbulence components.
3.2.7.1 Discussion—This ratio is used to compensate for
Thequasi-instantaneousvelocitycomponentmeasurementsare
effects of along-axis flow shadowing by the transducers and
averaged over user-selected sampling times to define mean
their supporting structure.
along-axis wind components, mean wind speed and direction,
3.2.8 transit time (t, (s))—the time required for an acoustic
and the variances or covariances, or both, of individual
wavefront to travel from the transducer of origin to the
componentsorcomponentcombinations.Covariancesareused
receiving transducer.
for eddy correlation studies and for computation of boundary
3.3 Symbols:
layer heat and momentum fluxes. The sonic anemometer/
B (dimensionless) squared sums of sines and cosines of wind direction
thermometerprovidesthedatarequiredtocharacterizethestate
angle used to calculate wind direction standard devia-
of the turbulent atmospheric boundary layer.
tion
c (m/s) speed of sound 5.2 The sonic anemometer/thermometer array shall have a
d (m) acoustic pathlength
sufficiently high structural rigidity and a sufficiently low
e (Pa) vapor pressure of water
coefficient of thermal expansion to maintain an internal align-
f (dimensionless) compressibility factor
P (Pa) ambient pressure
ment to within 60.1°. System electronics must remain stable
t (s) transit time
over its operating temperature range; the time counter oscilla-
T (K) absolute temperature, K
tor instability must not exceed 0.01% of frequency. Consult
T (K) sonic temperature, K
s
g (dimensionless) specific heat ratio (c /c ) with the manufacturer for an internal alignment verification
p v
M (g/mol) molar mass of air
procedure.
n (dimensionless) sample size
5.3 The calculations and transformations provided in these
R* (J/mol·K) the universal gas constant
u (m/s) velocity component along the determined mean wind di-
practices apply to orthogonal arrays. References are also
rection
provided for common types of non-orthogonal arrays.
u (m/s) velocity component along the array u axis
s
v (m/s) velocity component crosswind to the determined mean
wind direction
6. Interferences
v (m/s) velocity component along the array v axis
s
w (m/s) vertical velocity 6.1 Mount the sonic anemometer probe for an acceptance
WS (m/s) scalar wind speed computed from measured velocity
angle into the mean wind. Wind velocity components from
components in the horizontal plane
angles outside the acceptance angle may be subject to uncom-
u (deg) determined mean wind direction with respect to true
north pensated flow blockage effects from the transducers and
u (deg) wind direction measured in degrees clockwise from the
r
supporting structure, or may not be unambiguously defined.
sonic anemometer + v axis to the along-wind u axis
s
Obtain acceptance angle information from the manufacturer.
a (deg) acceptance angle
f (deg) orientation of the sonic anemometer axis with respect to
6.2 Mount the sonic array at a distance that exceeds the
the true north
acoustic pathlength by a factor of at least 2p from any
s (deg) standard deviation of wind azimuth angle
u
reflecting surface.
3.4 Abbreviations:Units—Units of measurement used
6.3 To obtain representative samples of the mean wind, the
should be in accordance with Practice IEEE/ASTM SI-10.
sonic array must be exposed at a representative site. Sonic
anemometer/thermometers are typically mounted over level,
4. Summary of Practice
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
4.5 Variances, covariances, and turbulence intensities are
not significantly different from zero. Arrays mounted above a
computed.
sloping surface may require tilt angle adjustments.Also, avoid
mounting the array close (within 2 m) to the ground surface
Excerpts from IEEE/ASTM SI-10 are included in Vol 11.07. where velocity gradients are large and w may be nonzero.
D5527–00 (2007)
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 these practices
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
softwaremodificationsnotaddressedinthesepracticesmaybeneededfor
manufacturer should include transducer shadow corrections as
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 Thesepracticesdonotaddressapplicationswheremois-
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 ).
si
8. Procedure
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 ).
si
(refer to the manufacturer’s instructions).
9.2.3 Averticalwindcomponententeringthearrayfromthe
8.2 Mount the instrument array on a solid, vibration-free
bottom will have a positive sign (+w ).
si
platform free of interferences.
9.2.4 The subscript s refers to a wind componen
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
An American National Standard Designation: D 5527 – 00 (Reapproved 2007)
Designation:D5527–94
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.
1. Scope
1.1 Thiese practices 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 appliesThese practices apply to the measurement of wind velocity components over horizontal terrain
using instruments mounted on stationary towers. Thiese practices also appliesapply to speed of sound measurements that are
converted to sonic temperatures but doesdo 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.
2. Referenced Documents
2.1 ASTM Standards:
D1356 Terminology Relating to Sampling and Analysis of Atmospheres
D3631 Test Methods for Measuring Surface Atmospheric Pressure
D4230 Test Method of Measuring Humidity with Cooled-Surface Condensation (Dew-Point) Hygrometer
E337 Test Method for Measuring Humidity with a Psychrometer (the Measurement of Wet- and Dry-Bulb Temperatures)
E380Practice for Use of the International System of Units (SI) (the Modernized Metric System) IEEE/ASTM SI-10 American
National Standard for Use
of the International System
of Units (SI): The Modern
Metric System
3. Terminology
3.1Definitions:
3.1.1
3.1 Definitions— Refer to Terminology D1356 for common terminology.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 acceptance angle (6a, deg)— the angular distance, centered on the array axis of symmetry, over which the following
conditionsaremet:(a)windcomponentsareunambiguouslydefined,and(b)flowacrossthetransducersisunobstructedorremains
within the angular range for which transducer shadow corrections are defined.
3.1.2
3.2.2 acoustic pathlength (d, (m))—the physical distance between transducer transmitter-receiver pairs.
3.1.33.2.3 sampling period(s)—the record length or time interval over which data collection occurs.
3.1.4
3.2.4 sampling rate (Hz)—the rate at which data collection occurs, usually presented in samples per second or Hertz.
3.1.5
This practice is under the jurisdiction of ASTM Committee D-22 on Sampling and Analysis of Atmospheres and is the direct responsibility of Subcommittee D22.11
on Meteorology.
Current edition approved March 15, 1994. Published May 1994.
These practices are under the jurisdiction of ASTM Committee D22 on Air Quality and are the direct responsibility of Subcommittee D22.11 on Meteorology.
e1
Current edition approved Oct. 1, 2007. Published December 2007. Originally approved in 1994. Last previous edition approved in 2002 as D5527-00(2002) .
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.For Annual Book of ASTM Standards
, Vol 11.03.volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D5527–00 (2007)
3.2.5 sonic anemometer/thermometer—an instrument consisting of a transducer array containing paired sets of acoustic
transmitters and receivers, a system clock, and microprocessor circuitry to measure intervals of time between transmission and
reception of sound pulses.
3.1.5.1
3.2.5.1 Discussion—The fundamental measurement unit is transit time. With transit time and a known acoustic pathlength,
velocity or speed of sound, or both, can be calculated. Instrument output is a series of quasi-instantaneous velocity component
readings along each axis or speed of sound, or both. The speed of sound and velocity components may be used to compute sonic
temperature (T ), to describe the mean wind field, or to compute fluxes, variances, and turbulence intensities.
s
3.1.6
3.2.6 sonic temperature (T ), (K))— an equivalent temperature that accounts for the effects of temperature and moisture on
s
acoustic wavefront propagation through the atmosphere.
3.1.6.1
3.2.6.1 Discussion—Sonic temperature is related to the velocity of sound c, absolute temperature T, vapor pressure of water e,
and absolute pressure P by (1).
c 5403T ~1 10.32e/P! 5403T (1)
s
(Guidance concerning measurement of P and e are contained in Test Methods D3631, D4230, and E337.)
3.1.7
3.2.7 transducer shadow correction—the ratio of the true along-axis velocity, as measured in a wind tunnel or by another
accepted method, to the instrument along-axis wind measurement.
3.1.7.1
3.2.7.1 Discussion—This ratio is used to compensate for effects of along-axis flow shadowing by the transducers and their
supporting structure.
3.1.8
3.2.8 transit time (t, (s))—the time required for an acoustic wavefront to travel from the transducer of origin to the receiving
transducer.
3.2
3.3 Symbols:
B (dimensionless) squared sums of sines and cosines of wind direction
angle used to calculate wind direction standard devia-
tion
c (m/s) speed of sound
d (m) acoustic pathlength
e (Pa) vapor pressure of water
f (dimensionless) compressibility factor
P (Pa) ambient pressure
t (s) transit time
T (K) absolute temperature, K
T (K) sonic temperature, K
s
g (dimensionless) specific heat ratio (c /c )
p v
M (g/mol) molar mass of air
n (dimensionless) sample size
R* (J/mol·K) the universal gas constant
u (m/s) velocity component along the determined mean wind di-
rection
u (m/s) velocity component along the array u axis
s
v (m/s) velocity component crosswind to the determined mean
wind direction
v (m/s) velocity component along the array v axis
s
w (m/s) vertical velocity
WS (m/s) wind speed computed from measured velocity compo-
nents
WS (m/s) scalar wind speed computed from measured velocity
components in the horizontal plane
u (deg) determined mean wind direction with respect to true
north
u (deg) wind direction measured in degrees clockwise from the
r
sonic anemometer + v axis to the along-wind u axis
s
a (deg) acceptance angle
f (deg) orientation of the sonic anemometer axis with respect to
the true north
s (deg) standard deviation of wind azimuth angle
u
3.3
Annual Book of ASTM Standards, Vol 14.02.
The boldface numbers in parentheses refer to the list of references at the end of these practices.
D5527–00 (2007)
3.4 Abbreviations:Units—Units of measurement used should be in accordance with Practice E380.
4. Summary of Practice
4.1 Acalibratedsonicanemometer/thermometerisinstalled,leveled,andorientedintotheexpectedwinddirectiontoensurethat
the measured along-axis velocity components fall within the instrument’s acceptance angle.
4.2 The wind components measured over a user-defined sampling period are averaged and subjected to a software rotation into
the mean wind. This rotation maximizes the mean along-axis wind component and reduces the mean cross-component v to zero.
4.3 Mean horizontal wind speed and direction are computed from the rotated wind components.
4.4 For the sonic thermometer, the speed of sound solution is obtained and converted to a sonic temperature.
4.5 Variances, covariances, and turbulence intensities are computed.
5. Significance and Use
5.1 Sonicanemometer/thermometersareusedtomeasureturbulentcomponentsoftheatmosphereexceptforconfinedareasand
very close to the ground. This practice appliesThese 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
variancesorcovariances,orboth,ofindividualcomponentsorcomponentcombinations.Covariancesareusedforeddycorrelation
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.
5.2 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 60.1°. 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.
5.3 The calculations and transformations provided in thiese practices apply to orthogonal arrays. References are also provided
for common types of non-orthogonal arrays.
6. Interferences
6.1 Mount the sonic anemometer probe for an acceptance angle into the mean wind. Wind velocity components from angles
outsidetheacceptanceanglemaybesubjecttouncompensatedflowblockageeffectsfromthetransducersandsupportingstructure,
or may not be unambiguously defined. Obtain acceptance angle information from the manufacturer.
6.2 Mountthesonicarrayatadistancethatexceedstheacousticpathlengthbyafactorofatleast2pfromanyreflectingsurface.
6.3 To obtain representative samples of the mean wind, the sonic array must be exposed at a representative site. Sonic
anemometer/thermometers are typically mounted over level, open terrain at a height of 10 m above the ground. Consider surface
roughness and obstacles that might cause flow blockage or biases in the site selection process.
6.4 Carefully measure and verify array tilt angle and alignment. The vertical component of the wind is usually much smaller
than the horizontal components. Therefore, the vertical wind component is highly susceptible to cross-component contamination
from tilt angles not aligned to the chosen coordinate system. A typical coordinate system may include establishing a level with
reference to either the earth or to local terrain slope. Momentum flux computations are particularly susceptible to off-axis
contamination (2). Calculations and transformations (Section 9) for sonic anemometer data are based on the assumption that the
meanverticalvelocity(w w)isnotsignificantlydifferentfromzero.Arraysmountedaboveaslopingsurfacemayrequiretiltangle
adjustments. Also, avoid mounting the array close (within 2 m) to the ground surface where velocity gradients are large and w
wmay be nonzero.
6.5 Thetransducersaretinymicrophonesandare,therefore,sensitivetoextraneousnoisesources,especiallyultrasonicsources
at the anemometer’s operating frequency. Mount the transducer array in an environment free of extraneous noise sources.
6.6 Sonic anemometer/thermometer transducer arrays contribute a certain degree of blockage to flow. Consequently, the
manufacturershouldincludetransducershadowcorrectionsaspartoftheinstrument’sdataprocessingalgorithms,ordefine,define
an acceptance angle beyond which valid measurements cannot be made, or both.
6.7 Ensure that the instrument is operated within its velocity calibration range and at temperatures where thermal sensitivity
effects are not observed.
6.8Thispracticedoes6.8 Thesepracticesdonotaddressapplicationswheremoistureislikelytoaccumulateonthetransducers.
Moisture accumulation may interrupt transmission of the acoustic signal, or possibly damage unsealed transducers. Consult the
manufacturer concerning operation in adverse environments.
7. Sampling
7.1 The basic sampling rate of a sonic anemometer is on the order of several hundred hertz. Transit times are averaged within
the instrument’s software to produce basic measurements at a rate of 10 to 20 Hz, which may be user-selectable. This sampling
The boldface numbers in parentheses refer to the list of references at the end of this practice.
Excerpts from IEEE/ASTM SI-10 are included in Vol 11.07.
D5527–00 (2007)
is done to improve instrument measurement precision and to suppress high frequency noise and aliasing effects. The 10 to 20-Hz
sample output in a serial digital data stream or through a digital to analog converter is the basic unit of measurement for a sonic
anemometer.
7.2 Select a sampling period of sufficient duration to obtain statistically stable measurements of the phenomena of interest.
Samplingperiodsofatleast10mindurationusuallygeneratesufficientdatatodescribetheturbulentstateoftheatmosphereduring
steady wind conditions. Sampling periods in excess of 1 h may contain undesired trends in wind direction.
8. Procedure
8.1 Perform system calibration in a zero wind chamber (refer to the manufacturer’s instructions).
8.2 Mount the instrument array on a solid, vibration-free platform free of interferences.
8.3 Select an orientation into the mean flow within the instrument’s acceptance angle. Record the orientation angle with a
resolution of 1°. Use a leveling device to position the probe to within 60.1° of the vertical axis of the chosen coordinate system.
NOTE 1—Caution:Wind measurements using a sonic anemometer should only be made within the acceptance angle.
8.4 Install cabling to the recording device, and keep cabling isolated from other electronics noise sources or power cables to
minimize induction or crosstalk.
8.5 Asasystemcheck,collectdataforseveralsequentialsamplingperiods(ofatleast10-mindurationoveraperiodofatleast
1 h) during representative operating conditions. Examine data samples for extraneous spikes, noise, alignment faults, or other
malfunctions. Construct summary statistics for each sampling period to include means, variances, and covariances; examine these
statisticsforreasonableness.Compute1-hspectraandexamineforspikesoraliasingaffectingthe−5/3spectralslopeintheinertial
subrange.
NOTE 2—Calculations and transformations presented in thiese practices are based on the assumption of a zero mean vertical velocity component.
Devi
...
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