ASTM D5527-23

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 in 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 sensor 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 using 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, health, and environmental 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

• Status: Published
• Publication Date: 31-Aug-2023
• ICS: 07.060 - Geology. Meteorology. Hydrology
• Technical Committee: D22 - Air Quality
• Drafting Committee: D22.11 - Meteorology

Relations

• Refers: ASTM D1356-20a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Sep-2020
• Refers: ASTM D1356-20 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Mar-2020
• Refers: ASTM D4230-20 - Standard Test Method for Measuring Humidity with Cooled-Surface Condensation (Dew-Point) Hygrometer
• Effective Date: 01-Mar-2020
• Refers: ASTM D3631-99(2017) - Standard Test Methods for Measuring Surface Atmospheric Pressure
• Effective Date: 01-Mar-2017
• Refers: ASTM D1356-15a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Oct-2015
• Refers: ASTM D1356-15 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Jul-2015
• Refers: ASTM D1356-14b - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Dec-2014
• Refers: ASTM D1356-14a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-May-2014
• Refers: ASTM D1356-14 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Jan-2014
• Refers: ASTM D4230-02(2012) - Standard Test Method of Measuring Humidity with Cooled-Surface Condensation (Dew-Point) Hygrometer
• Effective Date: 01-Apr-2012
• Refers: ASTM D3631-99(2011) - Standard Test Methods for Measuring Surface Atmospheric Pressure
• Effective Date: 01-Oct-2011
• Refers: ASTM D1356-05(2010) - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Apr-2010
• Refers: ASTM D4230-02(2007) - Standard Test Method of Measuring Humidity with Cooled-Surface Condensation (Dew-Point) Hygrometer
• Effective Date: 01-Oct-2007
• Refers: ASTM E337-02(2007) - Standard Test Method for Measuring Humidity with a Psychrometer (the Measurement of Wet- and Dry-Bulb Temperatures)
• Effective Date: 01-Oct-2007
• Refers: ASTM D3631-99(2007) - Standard Test Methods for Measuring Surface Atmospheric Pressure
• Effective Date: 01-Oct-2007

Overview

ASTM D5527-23: Standard Practices for Measuring Surface Wind and Temperature by Acoustic Means provides guidelines for the field measurement of wind components and sonic temperature using sonic anemometer/thermometers. This standard is essential for atmospheric research, environmental monitoring, and meteorological applications, where accurate measurement of wind turbulence and temperature is crucial. Instruments utilizing the inverse time measurement technique are addressed, focusing on the measurement of one-, two-, or three-dimensional wind vectors and the corresponding sonic temperature.

By establishing consistent practices for sensor installation, alignment, calibration, data gathering, and data processing, ASTM D5527-23 ensures reliable and comparable results in the study of the atmospheric boundary layer and related turbulence.

Key Topics

• Instrument Selection and Calibration

  • Use of sonic anemometer/thermometers for field measurements of wind and temperature
  • System calibration in zero wind chambers and regular alignment checks

• Installation and Environmental Considerations

  • Proper mounting over horizontal, open terrain, typically at 10 meters above ground
  • Avoidance of flow obstructions, extraneous noise, and proximity to the ground or reflective surfaces

• Data Collection and Processing

  • User-defined sampling rates and periods for gathering statistically stable data
  • Calculation of mean wind speed, direction, scalar and vector components, variances, covariances, and turbulence intensities
  • Data corrections for transducer shadowing and array tilt

• Measurement Technique

  • Use of the inverse time measurement technique to derive wind velocity and speed of sound
  • Conversion of speed of sound to sonic temperature, accounting for atmospheric properties

• Quality Assurance

  • Regular system performance checks and examination for noise, spikes, or alignment faults
  • Adherence to data selection periods to avoid wind direction trends

Applications

The practices in ASTM D5527-23 are widely applicable in fields that require precise measurement and analysis of atmospheric conditions:

• Meteorological Research

  • Characterizing turbulence and boundary layer processes
  • Supporting studies of atmospheric heat and momentum fluxes, eddy correlation, and climatology

• Environmental Monitoring

  • Collecting wind and temperature data for air quality and dispersion modeling
  • Regulatory compliance applications for ambient air monitoring at industrial and research sites

• Wind Energy and Siting Studies

  • Assessing wind resources and turbine site suitability through detailed wind profile measurements

• Agricultural and Forestry Meteorology

  • Evaluating microclimate conditions that affect crop growth and forest management

• Urban and Regional Planning

  • Supporting urban microclimate studies and infrastructure design where wind characteristics impact safety and comfort

Related Standards

Users of ASTM D5527-23 often reference additional documents for a comprehensive approach to atmospheric measurement:

• ASTM D1356 – Terminology Relating to Sampling and Analysis of Atmospheres
• ASTM D3631 – Test Methods for Measuring Surface Atmospheric Pressure
• ASTM D4230 – Test Method for Measuring Humidity with Cooled-Surface Condensation (Dew-Point) Hygrometer
• ASTM E337 – Test Method for Measuring Humidity with a Psychrometer
• IEEE/ASTM SI-10 – American National Standard for Use of the International System of Units (SI): The Modern Metric System

By following ASTM D5527-23 and related standards, professionals ensure accurate, repeatable, and internationally recognized wind and temperature measurements for a broad range of scientific and regulatory applications.

Standards Content (Sample)

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.
Designation: D5527 − 23
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.
1. Scope D4230 Test Method for 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 using ancillary temperature devices.
3.1 Definitions—Refer to Terminology D1356 for common
1.2 The values stated in SI units are to be regarded as
terminology.
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), n—the angular distance,
1.3 This standard does not purport to address all of the
centered on the array axis of symmetry, over which the
safety concerns, if any, associated with its use. It is the
following conditions are met: (a) wind components are unam-
responsibility of the user of this standard to establish appro-
biguously defined, and (b) flow across the transducers is
priate safety, health, and environmental practices and deter-
unobstructed or remains within the angular range for which
mine the applicability of regulatory limitations prior to use.
transducer shadow corrections are defined.
1.4 This international standard was developed in accor-
dance with internationally recognized principles on standard-
3.2.2 acoustic pathlength (d, (m)), n—the distance between
ization established in the Decision on Principles for the
transducer transmitter-receiver pairs.
Development of International Standards, Guides and Recom-
3.2.3 sampling period(s), n—the length or time interval over
mendations issued by the World Trade Organization Technical
which data collection occurs.
Barriers to Trade (TBT) Committee.
3.2.4 sampling rate (Hz), n—the rate at which data collec-
2. Referenced Documents tion occurs, usually presented in samples per second or Hertz.
2.1 ASTM Standards:
3.2.5 sonic anemometer/thermometer, n—an instrument
D1356 Terminology Relating to Sampling and Analysis of
consisting of a transducer array containing paired sets of
Atmospheres
acoustic transmitters and receivers, a system clock, and micro-
D3631 Test Methods for Measuring Surface Atmospheric
processor circuitry to measure intervals of time between
Pressure
transmission and reception of sound pulses.
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 Sept. 1, 2023. Published September 2023. Originally
ɛ1
component readings along each axis or speed of sound, or both.
approved in 1994. Last previous edition approved in 2017 as D5527 – 00 (2017) .
DOI: 10.1520/D5527-23.
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 [e-mail]. 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
D5527 − 23
3.2.6 sonic temperature (T ), (K)), n—an equivalent tem- 4.2 The wind components measured over a user-defined
s
perature that accounts for the effects of temperature and sampling period are averaged and subjected to a software
moisture on acoustic wavefront propagation through the atmo- rotation into the mean wind direction. This rotation maximizes
sphere. the mean along-axis wind component and reduces the mean
3.2.6.1 Discussion—Sonic temperature is related to the cross-component v to zero.
velocity of sound c, absolute temperature T, vapor pressure of
4.3 Mean horizontal wind speed and direction are computed
water e, and absolute pressure P by (1).
from the rotated wind components.
c 5 403T 110.32e/P 5 403T (1)
~ !
s
4.4 For the sonic thermometer, the speed of sound solution
(Guidance concerning measurement of P and e are con-
is obtained and converted to a sonic temperature.
tained in Test Methods D3631, D4230, and E337.)
4.5 Variances, covariances, and turbulence intensities are
3.2.7 transducer shadow correction, n—the ratio of the true
computed.
along-axis velocity, as measured in a wind tunnel or by another
accepted method, to the instrument along-axis wind measure-
5. Significance and Use
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 in confined
effects of along-axis flow shadowing by the transducers and
areas and very close to the ground. These practices apply to the
their supporting structure.
use of these instruments for field measurement of the wind,
3.2.8 transit time (t, (s)), n—the time required for an
sonic temperature, and atmospheric turbulence components.
acoustic wavefront to travel from the transducer of origin to the
The quasi-instantaneous velocity component measurements are
receiving transducer.
averaged over user-selected sampling times to define mean
3.3 Symbols: along-axis wind components, mean wind speed and direction,
and the variances or covariances, or both, of individual
B (dimensionless) squared sums of sines and cosines of wind direction
angle used to calculate wind direction standard
components or component combinations. Covariances are used
deviation
for eddy correlation studies and for computation of boundary
c (m/s) speed of sound
layer heat and momentum fluxes. The sonic anemometer/
d (m) acoustic pathlength
e (Pa) vapor pressure of water
thermometer provides the data required to characterize the state
f (dimensionless) compressibility factor
of the turbulent atmospheric boundary layer.
P (Pa) ambient pressure
t (s) transit time
5.2 The sonic anemometer/thermometer array shall have a
T (K) absolute temperature, K
sufficiently high structural rigidity and a sufficiently low
T (K) sonic temperature, K
s
γ (dimensionless) specific heat ratio (c /c )
p v coefficient of thermal expansion to maintain an internal align-
M (g/mol) molar mass of air
ment to within 60.1°. System electronics must remain stable
n (dimensionless) sample size
over its operating temperature range; the time counter oscilla-
R* (J/mol·K) the universal gas constant
u (m/s) velocity component along the determined mean wind
tor instability must not exceed 0.01 % of frequency. Consult
direction
with the sensor manufacturer for an internal alignment verifi-
u (m/s) velocity component along the array u axis
s
cation procedure.
v (m/s) velocity component crosswind to the determined mean
wind direction
5.3 The calculations and transformations provided in these
v (m/s) velocity component along the array v axis
s
w (m/s) vertical velocity
practices apply to orthogonal arrays. References are also
WS (m/s) scalar wind speed computed from measured velocity
provided for common types of non-orthogonal arrays.
components in the horizontal plane
θ (deg) determined mean wind direction with respect to true
north
6. Interferences
θ (deg) wind direction measured in degrees clockwise from the
r
sonic anemometer + v axis to the along-wind u axis
6.1 Mount the sonic anemometer probe for an acceptance
s
α (deg) acceptance angle
angle into the mean wind. Wind velocity components from
φ (deg) orientation of the sonic anemometer axis with respect to
angles outside the acceptance angle may be subject to uncom-
the true north
σ (deg) standard deviation of wind azimuth angle
pensated flow blockage effects from the transducers and
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 IEEE/ASTM SI-10.
6.2 Mount the sonic array at a distance that exceeds the
4. Summary of Practice
acoustic pathlength by a factor of at least 2π from any
4.1 A calibrated sonic anemometer/thermometer is installed,
reflecting surface.
leveled, and oriented into the expected wind direction to ensure
6.3 To obtain representative samples of the mean wind, the
that the measured along-axis velocity components fall within
sonic array must be exposed at a representative site. Sonic
the instrument’s acceptance angle.
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.
D5527 − 23
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 assume
minimize induction or crosstalk.
that the mean vertical velocity w¯ is not significantly different
~ !
8.5 As a system check, collect data for several sequential
from zero. Arrays mounted above a sloping surface may
sampling periods (of at least 10 min duration over a period of
require tilt angle adjustments. Also, avoid mounting the array
at least 1 h) during representative operating conditions. Exam-
close (within 2 m) to the ground surface where velocity
ine data samples for extraneous spikes, noise, alignment faults,
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, especially ultrasonic sources at
examine these statistics for reasonableness. Compute 1 h
the anemometer’s operating frequency. Mount the transducer
spectra and examine for spikes or aliasing affecting the − 5 ⁄3
array in an environment free o
...

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 2017) D5527 − 23
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 using 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 healthsafety, health, and environmental 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 for 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:
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 March 1, 2017Sept. 1, 2023. Published March 2017September 2023. Originally approved in 1994. Last previous edition approved in 20112017
ɛ1
as D5527 – 00 (2011).(2017) . DOI: 10.1520/D5527-00R17E01.10.1520/D5527-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. 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
D5527 − 23
3.2.1 acceptance angle (6α, deg)—deg), n—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))—(m)), n—the distance between transducer transmitter-receiver pairs.
3.2.3 sampling period(s)—period(s), n—the record length or time interval over which data collection occurs.
3.2.4 sampling rate (Hz)—(Hz), n—the rate at which data collection occurs, usually presented in samples per second or Hertz.
3.2.5 sonic anemometer/thermometer—anemometer/thermometer, n—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.
3.2.5.1 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))—(K)), n—an equivalent temperature that accounts for the effects of temperature and moisture
s
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 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—correction, n—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.
3.2.7.1 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))—(s)), n—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
The boldface numbers in parentheses refer to the list of references at the end of these practices.
D5527 − 23
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 IEEE/ASTM SI-10.
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. wind direction. 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 forin 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 sensor
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,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.
Excerpts from IEEE/ASTM SI-10 are included in Vol 11.07.
D5527 − 23
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 assume 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) 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, noise, especially ultrasonic
sources at the anemometer’s operating frequency. Mount the transducer array in an environment free of extraneous noise
sources.noise.
6.6 Sonic anemometer/thermometer transducer arrays contribute a certain degree of some blockage to flow. Consequently, the
manufacturer should include transducer shadow corrections as part of the instrument’s data processing algorithms,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
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