ASTM D5527-00(2017)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
5.1 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.
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 ±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.
5.3 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 standard. No other units of measurement are included in this 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.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
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´1
Designation: D5527 − 00 (Reapproved 2017)
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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Warning notes were editorially updated throughout in March 2017.
1. Scope D4230 Test Method of Measuring Humidity with Cooled-
Surface Condensation (Dew-Point) Hygrometer
1.1 These practices cover procedures for measuring one-,
E337 Test Method for Measuring Humidity with a Psy-
two-, or three-dimensional vector wind components and sonic
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
temperature by means of commercially available sonic
peratures)
anemometer/thermometers that employ the inverse time mea-
IEEE/ASTM SI-10 American National Standard for Use of
surement technique. These practices apply to the measurement
the International System of Units (SI): The Modern Metric
of wind velocity components over horizontal terrain using
System
instruments mounted on stationary towers. These practices also
apply to speed of sound measurements that are converted to
3. Terminology
sonic temperatures but do not apply to the measurement of
temperature by the use of ancillary temperature devices.
3.1 Definitions—Refer to Terminology D1356 for common
terminology.
1.2 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
3.2 Definitions of Terms Specific to This Standard:
standard.
3.2.1 acceptance angle (6α, deg)— the angular distance,
centered on the array axis of symmetry, over which the
1.3 This standard does not purport to address all of the
following conditions are met: (a) wind components are unam-
safety concerns, if any, associated with its use. It is the
biguously defined, and (b) flow across the transducers is
responsibility of the user of this standard to establish appro-
unobstructed or remains within the angular range for which
priate safety and health practices and determine the applica-
transducer shadow corrections are defined.
bility of regulatory limitations prior to use.
1.4 This international standard was developed in accor-
3.2.2 acoustic pathlength (d, (m))—the distance between
dance with internationally recognized principles on standard-
transducer transmitter-receiver pairs.
ization established in the Decision on Principles for the
3.2.3 sampling period(s)—the record length or time interval
Development of International Standards, Guides and Recom-
over which data collection occurs.
mendations issued by the World Trade Organization Technical
3.2.4 sampling rate (Hz)—the rate at which data collection
Barriers to Trade (TBT) Committee.
occurs, usually presented in samples per second or Hertz.
2. Referenced Documents
3.2.5 sonic anemometer/thermometer—an instrument con-
2.1 ASTM Standards:
sisting of a transducer array containing paired sets of acoustic
D1356 Terminology Relating to Sampling and Analysis of
transmitters and receivers, a system clock, and microprocessor
Atmospheres
circuitry to measure intervals of time between transmission and
D3631 Test Methods for Measuring Surface Atmospheric
reception of sound pulses.
Pressure
3.2.5.1 Discussion—The fundamental measurement unit is
transit time. With transit time and a known acoustic pathlength,
These practices are under the jurisdiction of ASTM Committee D22 on Air
velocity or speed of sound, or both, can be calculated.
Quality and are the direct responsibility of Subcommittee D22.11 on Meteorology.
Instrument output is a series of quasi-instantaneous velocity
Current edition approved March 1, 2017. Published March 2017. Originally
component readings along each axis or speed of sound, or both.
approved in 1994. Last previous edition approved in 2011 as D5527 – 00 (2011).
DOI: 10.1520/D5527-00R17E01.
The speed of sound and velocity components may be used to
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
compute sonic temperature (T ), to describe the mean wind
s
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
field, or to compute fluxes, variances, and turbulence intensi-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. ties.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D5527 − 00 (2017)
3.2.6 sonic temperature (T ), (K))— an equivalent tempera- 4.2 The wind components measured over a user-defined
s
ture that accounts for the effects of temperature and moisture sampling period are averaged and subjected to a software
on acoustic wavefront propagation through the atmosphere. rotation into the mean wind. This rotation maximizes the mean
3.2.6.1 Discussion—Sonic temperature is related to the along-axis wind component and reduces the mean cross-
velocity of sound c, absolute temperature T, vapor pressure of component v to zero.
water e, and absolute pressure P by (1).
4.3 Mean horizontal wind speed and direction are computed
c 5 403T 110.32e/P 5 403T (1)
~ ! from the rotated wind components.
s
(Guidance concerning measurement of P and e are con-
4.4 For the sonic thermometer, the speed of sound solution
tained in Test Methods D3631, D4230, and E337.) is obtained and converted to a sonic temperature.
3.2.7 transducer shadow correction—the ratio of the true
4.5 Variances, covariances, and turbulence intensities are
along-axis velocity, as measured in a wind tunnel or by another
computed.
accepted method, to the instrument along-axis wind measure-
ment.
5. Significance and Use
3.2.7.1 Discussion—This ratio is used to compensate for
5.1 Sonic anemometer/thermometers are used to measure
effects of along-axis flow shadowing by the transducers and
turbulent components of the atmosphere except for confined
their supporting structure.
areas and very close to the ground. These practices apply to the
3.2.8 transit time (t, (s))—the time required for an acoustic
use of these instruments for field measurement of the wind,
wavefront to travel from the transducer of origin to the
sonic temperature, and atmospheric turbulence components.
receiving transducer.
The quasi-instantaneous velocity component measurements are
3.3 Symbols: averaged over user-selected sampling times to define mean
along-axis wind components, mean wind speed and direction,
B (dimensionless) squared sums of sines and cosines of wind direction
angle used to calculate wind direction standard
and the variances or covariances, or both, of individual
deviation
components or component combinations. Covariances are used
c (m/s) speed of sound
for eddy correlation studies and for computation of boundary
d (m) acoustic pathlength
e (Pa) vapor pressure of water
layer heat and momentum fluxes. The sonic anemometer/
f (dimensionless) compressibility factor
thermometer provides the data required to characterize the state
P (Pa) ambient pressure
of the turbulent atmospheric boundary layer.
t (s) transit time
T (K) absolute temperature, K
5.2 The sonic anemometer/thermometer array shall have a
T (K) sonic temperature, K
s
γ (dimensionless) specific heat ratio (c /c )
p v sufficiently high structural rigidity and a sufficiently low
M (g/mol) molar mass of air
coefficient of thermal expansion to maintain an internal align-
n (dimensionless) sample size
ment to within 60.1°. System electronics must remain stable
R* (J/mol·K) the universal gas constant
u (m/s) velocity component along the determined mean wind
over its operating temperature range; the time counter oscilla-
direction
tor instability must not exceed 0.01 % of frequency. Consult
u (m/s) velocity component along the array u axis
s
with the manufacturer for an internal alignment verification
v (m/s) velocity component crosswind to the determined mean
wind direction
procedure.
v (m/s) velocity component along the array v axis
s
w (m/s) vertical velocity
5.3 The calculations and transformations provided in these
WS (m/s) scalar wind speed computed from measured velocity
practices apply to orthogonal arrays. References are also
components in the horizontal plane
provided for common types of non-orthogonal arrays.
θ (deg) determined mean wind direction with respect to true
north
θ (deg) wind direction measured in degrees clockwise from the
r
6. Interferences
sonic anemometer + v axis to the along-wind u axis
s
α (deg) acceptance angle
6.1 Mount the sonic anemometer probe for an acceptance
φ (deg) orientation of the sonic anemometer axis with respect to
angle into the mean wind. Wind velocity components from
the true north
σ (deg) standard deviation of wind azimuth angle
angles outside the acceptance angle may be subject to uncom-
θ
pensated flow blockage effects from the transducers and
3.4 Units—Units of measurement used should be in accor-
supporting structure, or may not be unambiguously defined.
dance with IEEE/ASTM SI-10.
Obtain acceptance angle information from the manufacturer.
4. Summary of Practice
6.2 Mount the sonic array at a distance that exceeds the
4.1 A calibrated sonic anemometer/thermometer is installed, acoustic pathlength by a factor of at least 2π from any
leveled, and oriented into the expected wind direction to ensure
reflecting surface.
that the measured along-axis velocity components fall within
6.3 To obtain representative samples of the mean wind, the
the instrument’s acceptance angle.
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
The boldface numbers in parentheses refer to the list of references at the end of
surface roughness and obstacles that might cause flow block-
these practices.
Excerpts from IEEE/ASTM SI-10 are included in Vol 11.07. age or biases in the site selection process.
´1
D5527 − 00 (2017)
6.4 Carefully measure and verify array tilt angle and align- 8.3 Select an orientation into the mean flow within the
ment. The vertical component of the wind is usually much instrument’s acceptance angle. Record the orientation angle
smaller than the horizontal components. Therefore, the vertical with a resolution of 1°. Use a leveling device to position the
wind component is highly susceptible to cross-component probe to within 60.1° of the vertical axis of the chosen
contamination from tilt angles not aligned to the chosen coordinate system. (Warning—Wind measurements using a
coordinate system. A typical coordinate system may include sonic anemometer should only be made within the acceptance
establishing a level with reference to either the earth or to local angle.)
terrain slope. Momentum flux computations are particularly
8.4 Install cabling to the recording device, and keep cabling
susceptible to off-axis contamination (2). Calculations and
isolated from other electronics noise sources or power cables to
transformations (Section 9) for sonic anemometer data are
minimize induction or crosstalk.
based on the assumption that the mean vertical velocity ~w¯! is
8.5 As a system check, collect data for several sequential
not significantly different from zero. Arrays mounted above a
sampling periods (of at least 10-min duration over a period of
sloping surface may require tilt angle adjustments. Also, avoid
at least 1 h) during representative operating conditions. Exam-
mounting the array close (within 2 m) to the ground surface
ine data samples for extraneous spikes, noise, alignment faults,
where velocity gradients are large and w¯ may be nonzero.
or other malfunctions. Construct summary statistics for each
6.5 The transducers are tiny microphones and are, therefore,
sampling period to include means, variances, and covariances;
sensitive to extraneous noise sources, especially ultrasonic
examine these statistics for reasonableness. Compute 1-h
sources at the anemometer’s operating frequency. Mount the
spectra and examine for spikes or aliasing affecting the − 5 ⁄3
transducer array in an environment free of extraneous noise
spectral slope in the inertial subrange.
sources.
NOTE 1—Calculations and transformations presented in these practices
6.6 Sonic anemometer/thermometer transducer arrays con-
are based on the assumption of a zero mean vertical velocity component.
tribute a certain degree of blockage to flow. Consequently, the
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
software modifications not addressed in these practices may be needed for
part of the instrument’s data processing algorithms, or define
locations where w is nonzero.
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 Ensure that the instrument is operated within its velocity
significant change in weather conditions, or when transducers
calibration range and at temperatures where thermal sensitivity
or electronics components are changed or adjusted.
effects are not observed.
8.7 Check for bias, especially in w, using a data set collected
6.8 These practices do 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
accumulation may interrupt transmission of the acoustic signal,
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
7. Sampling
supporting structure is possible when the vertical angle of the
approaching wind exceeds 615°.)
7.1 The basic sampling rate of a sonic anemometer is on the
order of several hundred hertz. Transit times are averaged
9. Calculations and Transformations
within the instrument’s software to produce basic measure-
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 alig
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM 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.
´1
Designation: D5527 − 00 (Reapproved 2011) D5527 − 00 (Reapproved 2017)
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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Warning notes were editorially updated throughout in March 2017.
1. 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. No other units of measurement are included in this 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.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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)
IEEE/ASTM SI-10 American National Standard for Use of the International System of Units (SI): The Modern Metric System
3. Terminology
3.1 Definitions—Refer to Terminology D1356 for common terminology.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 acceptance angle (6α, deg)— the angular distance, centered on the array axis of symmetry, over which the following
conditions are met: (a) wind components are unambiguously defined, and (b) flow across the transducers is unobstructed or remains
within the angular range for which transducer shadow corrections are defined.
3.2.2 acoustic pathlength (d, (m))—the distance between transducer transmitter-receiver pairs.
3.2.3 sampling period(s)—the record length or time interval over which data collection occurs.
3.2.4 sampling rate (Hz)—the rate at which data collection occurs, usually presented in samples per second or Hertz.
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.
These practices are under the jurisdiction of ASTM Committee D22 on Air Quality and are the direct responsibility of Subcommittee D22.11 on Meteorology.
Current edition approved Oct. 1, 2011March 1, 2017. Published October 2011March 2017. Originally approved in 1994. Last previous edition approved in 20072011 as
D5527 – 00 (2007).(2017). DOI: 10.1520/D5527-00R11.10.1520/D5527-00R17E01.
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 the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D5527 − 00 (2017)
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
s
the mean wind field, or to compute fluxes, variances, and turbulence intensities.
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.
3.2.6.1 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 5 403T 110.32e/P 5 403T (1)
~ !
s
(Guidance concerning measurement of P and e are contained in Test Methods D3631, D4230, and E337.)
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.
The boldface numbers in parentheses refer to the list of references at the end of these practices.
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.
3.2.8 transit time (t, (s))—the time required for an acoustic wavefront to travel from the transducer of origin to the receiving
transducer.
3.3 Symbols:
B (dimensionless) squared sums of sines and cosines of wind direction
angle used to calculate wind direction standard
deviation
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
γ (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
direction
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) scalar wind speed computed from measured velocity
components in the horizontal plane
θ (deg) determined mean wind direction with respect to true
north
θ (deg) wind direction measured in degrees clockwise from the
r
sonic anemometer + v axis to the along-wind u axis
s
α (deg) acceptance angle
φ (deg) orientation of the sonic anemometer axis with respect to
the true north
σ (deg) standard deviation of wind azimuth angle
θ
3.4 Units—Units of measurement used should be in accordance with Practice IEEE/ASTM SI-10.
Excerpts from IEEE/ASTM SI-10 are included in Vol 11.07.
´1
D5527 − 00 (2017)
4. Summary of Practice
4.1 A calibrated sonic anemometer/thermometer is installed, leveled, and oriented into the expected wind direction to ensure that
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 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.
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 these 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
outside the acceptance angle may be subject to uncompensated flow blockage effects from the transducers and supporting structure,
or may not be unambiguously defined. Obtain acceptance angle information from the manufacturer.
6.2 Mount the sonic array at a distance that exceeds the acoustic pathlength by a factor of at least 2π from any reflecting surface.
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
mean vertical velocity ~w¯ ! is not significantly different from zero. Arrays mounted above a sloping surface may require tilt angle
adjustments. Also, avoid mounting the array close (within 2 m) to the ground surface where velocity gradients are large and w¯ may
be nonzero.
6.5 The transducers are tiny microphones and are, therefore, sensitive to extraneous noise sources, especially ultrasonic sources
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
manufacturer should include transducer shadow corrections as part of the instrument’s data processing algorithms, or 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.
6.8 These practices do not address applications where moisture is likely to accumulate on the transducers. 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
´1
D5527 − 00 (2017)
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.
Sampling periods of at least 10 min duration usually generate sufficient data to describe the turbulent state of the atmosphere during
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.
(Warning—Wind measurements using a sonic anemometer should only be made within the acceptance angle.)
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 As a system check, collect data for several sequential sampling periods (of at least 10-min duration over a period of at least
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
statistics for reasonableness. Compute 1-h spectra and examine for spikes or aliasing affecting the − 5 ⁄3 spectral slope in the
inertial subrang
...
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