ASTM D5527-00
(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 This practice covers procedures for measuring one-, two-, or three-dimensional vector wind components and sonic temperature by means of commercially available sonic anemometer/thermometers that employ the inverse time measurement technique. This practice applies to the measurement of wind velocity components over horizontal terrain using instruments mounted on stationary towers. This practice also applies to speed of sound measurements that are converted to sonic temperatures but does not apply to the measurement of temperature by the use of ancillary temperature devices.
1.2 The values stated in SI units are to be regarded as the standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D 5527 – 00
Standard Practices for
Measuring Surface Wind and Temperature by Acoustic
Means
This standard is issued under the fixed designation D 5527; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.2 Definitions of Terms Specific to This Standard:
3.2.1 acceptance angle (6a, deg)— the angular distance,
1.1 This practice covers procedures for measuring one-,
centered on the array axis of symmetry, over which the
two-, or three-dimensional vector wind components and sonic
following conditions are met: (a) wind components are unam-
temperature by means of commercially available sonic
biguously defined, and (b) flow across the transducers is
anemometer/thermometers that employ the inverse time mea-
unobstructed or remains within the angular range for which
surement technique. This practice applies to the measurement
transducer shadow corrections are defined.
of wind velocity components over horizontal terrain using
3.2.2 acoustic pathlength (d, (m))—the distance between
instruments mounted on stationary towers. This practice also
transducer transmitter-receiver pairs.
applies to speed of sound measurements that are converted to
3.2.3 sampling period(s)—the record length or time interval
sonic temperatures but does not apply to the measurement of
over which data collection occurs.
temperature by the use of ancillary temperature devices.
3.2.4 sampling rate (Hz)—the rate at which data collection
1.2 The values stated in SI units are to be regarded as the
occurs, usually presented in samples per second or Hertz.
standard.
3.2.5 sonic anemometer/thermometer—an instrument con-
1.3 This standard does not purport to address all of the
sisting of a transducer array containing paired sets of acoustic
safety concerns, if any, associated with its use. It is the
transmitters and receivers, a system clock, and microprocessor
responsibility of the user of this standard to establish appro-
circuitry to measure intervals of time between transmission and
priate safety and health practices and determine the applica-
reception of sound pulses.
bility of regulatory limitations prior to use.
3.2.5.1 Discussion—The fundamental measurement unit is
2. Referenced Documents
transit time. With transit time and a known acoustic pathlength,
velocity or speed of sound, or both, can be calculated.
2.1 ASTM Standards:
Instrument output is a series of quasi-instantaneous velocity
D 1356 Standard Terminology Relating to Sampling and
component readings along each axis or speed of sound, or both.
Analysis of Atmospheres
The speed of sound and velocity components may be used to
D 3631 Test Methods for Measuring Surface Atmospheric
compute sonic temperature (T ), to describe the mean wind
s
Pressure
field, or to compute fluxes, variances, and turbulence intensi-
D 4230 Test Method of Measuring Humidity with Cooled-
ties.
Surface Condensation (Dew-Point) Hygrometer
3.2.6 sonic temperature (T ), (K))— an equivalent tempera-
E 337 Test Method for Measuring Humidity with a Psy- s
ture that accounts for the effects of temperature and moisture
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
on acoustic wavefront propagation through the atmosphere.
peratures)
3.2.6.1 Discussion—Sonic temperature is related to the
E 380 Practice for Use of the International System of Units
velocity of sound c, absolute temperature T, vapor pressure of
(SI) (the Modernized Metric System)
water e, and absolute pressure P by (1).
3. Terminology
c 5 403T ~1 1 0.32e/P! 5 403T (1)
s
3.1 Definitions—Refer to Terminology D 1356 for common
(Guidance concerning measurement of P and e are contained
terminology.
in Test Methods D 3631, D 4230, and E 337.)
3.2.7 transducer shadow correction—the ratio of the true
along-axis velocity, as measured in a wind tunnel or by another
This practice is under the jurisdiction of ASTM Committee D22 on Sampling
and Analysis of Atmospheres and is the direct responsibility of Subcommittee accepted method, to the instrument along-axis wind measure-
D22.11 on Meteorology.
ment.
Current edition approved Sept. 10, 2000. Published November 2000. Originally
published as D 5527 – 94. Last previous edition D 5527 – 94.
2 4
Annual Book of ASTM Standards, Vol 11.03. The boldface numbers in parentheses refer to the list of references at the end of
Annual Book of ASTM Standards, Vol 14.02. this practice.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 5527
3.2.7.1 Discussion—This ratio is used to compensate for use of these instruments for field measurement of the wind,
effects of along-axis flow shadowing by the transducers and sonic temperature, and atmospheric turbulence components.
their supporting structure. The quasi-instantaneous velocity component measurements are
3.2.8 transit time (t, (s))—the time required for an acoustic averaged over user-selected sampling times to define mean
wavefront to travel from the transducer of origin to the along-axis wind components, mean wind speed and direction,
receiving transducer. and the variances or covariances, or both, of individual
3.3 Symbols: components or component combinations. Covariances are used
for eddy correlation studies and for computation of boundary
B (dimensionless) squared sums of sines and cosines of wind direction
angle used to calculate wind direction standard devia-
layer heat and momentum fluxes. The sonic anemometer/
tion
thermometer provides the data required to characterize the state
c (m/s) speed of sound
d (m) acoustic pathlength of the turbulent atmospheric boundary layer.
e (Pa) vapor pressure of water
5.2 The sonic anemometer/thermometer array shall have a
f (dimensionless) compressibility factor
sufficiently high structural rigidity and a sufficiently low
P (Pa) ambient pressure
coefficient of thermal expansion to maintain an internal align-
t (s) transit time
T (K) absolute temperature, K
ment to within 60.1°. System electronics must remain stable
T (K) sonic temperature, K
s
over its operating temperature range; the time counter oscilla-
g (dimensionless) specific heat ratio (c /c )
p v
M (g/mol) molar mass of air tor instability must not exceed 0.01 % of frequency. Consult
n (dimensionless) sample size
with the manufacturer for an internal alignment verification
R* (J/mol·K) the universal gas constant
procedure.
u (m/s) velocity component along the determined mean wind di-
rection 5.3 The calculations and transformations provided in this
u (m/s) velocity component along the array u axis
s
practice apply to orthogonal arrays. References are also pro-
v (m/s) velocity component crosswind to the determined mean
vided for common types of non-orthogonal arrays.
wind direction
v (m/s) velocity component along the array v axis
s
6. Interferences
w (m/s) vertical velocity
WS (m/s) scalar wind speed computed from measured velocity
6.1 Mount the sonic anemometer probe for an acceptance
components in the horizontal plane
angle into the mean wind. Wind velocity components from
u (deg) determined mean wind direction with respect to true
north
angles outside the acceptance angle may be subject to uncom-
r
u (deg) wind direction measured in degrees clockwise from the
pensated flow blockage effects from the transducers and
sonic anemometer + v axis to the along-wind u axis
s
a (deg) acceptance angle supporting structure, or may not be unambiguously defined.
f (deg) orientation of the sonic anemometer axis with respect to
Obtain acceptance angle information from the manufacturer.
the true north
6.2 Mount the sonic array at a distance that exceeds the
s (deg) standard deviation of wind azimuth angle
u
acoustic pathlength by a factor of at least 2p from any
3.4 Abbreviations:Units—Units of measurement used
reflecting surface.
should be in accordance with Practice E 380.
6.3 To obtain representative samples of the mean wind, the
sonic array must be exposed at a representative site. Sonic
4. Summary of Practice
anemometer/thermometers are typically mounted over level,
4.1 A calibrated sonic anemometer/thermometer is installed,
open terrain at a height of 10 m above the ground. Consider
leveled, and oriented into the expected wind direction to ensure
surface roughness and obstacles that might cause flow block-
that the measured along-axis velocity components fall within
age or biases in the site selection process.
the instrument’s acceptance angle.
6.4 Carefully measure and verify array tilt angle and align-
4.2 The wind components measured over a user-defined
ment. The vertical component of the wind is usually much
sampling period are averaged and subjected to a software
smaller than the horizontal components. Therefore, the vertical
rotation into the mean wind. This rotation maximizes the mean
wind component is highly susceptible to cross-component
along-axis wind component and reduces the mean cross-
contamination from tilt angles not aligned to the chosen
component v to zero.
coordinate system. A typical coordinate system may include
4.3 Mean horizontal wind speed and direction are computed
establishing a level with reference to either the earth or to local
from the rotated wind components.
terrain slope. Momentum flux computations are particularly
4.4 For the sonic thermometer, the speed of sound solution
susceptible to off-axis contamination (2). Calculations and
is obtained and converted to a sonic temperature.
transformations (Section 9) for sonic anemometer data are
4.5 Variances, covariances, and turbulence intensities are
based on the assumption that the mean vertical velocity ( w )is
computed.
not significantly different from zero. Arrays mounted above a
sloping surface may require tilt angle adjustments. Also, avoid
5. Significance and Use
mounting the array close (within 2 m) to the ground surface
5.1 Sonic anemometer/thermometers are used to measure
where velocity gradients are large and w may be nonzero.
turbulent components of the atmosphere except for confined
6.5 The transducers are tiny microphones and are, therefore,
areas and very close to the ground. This practice applies to the
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
Excerpts from Practice E 380 are included in Vol 11.03. sources.
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 5527
Deviation of the mean vertical velocity component from zero should not
6.6 Sonic anemometer/thermometer transducer arrays con-
exceed the desired measurement precision. Alignment or data reduction
tribute a certain degree of blockage to flow. Consequently, the
software modifications not addressed in this practice may be needed for
manufacturer should include transducer shadow corrections as
locations where w is nonzero.
part of the instrument’s data processing algorithms, or define
8.6 Recalibrate and check instrument alignment at least
an acceptance angle beyond which valid measurements cannot
be made, or both. once a week, whenever the instrument is subjected to a
significant change in weather conditions, or when transducers
6.7 Ensure that the instrument is operated within its velocity
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 This practice does not address applications where mois-
over an extended time period. The array support structure,
ture is likely to accumulate on the transducers. Moisture topography, and changes in ambient temperature may produce
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
supporting structure is possible when the vertical angle of the
7. Sampling
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-
9.1 Each sonic anemometer provides wind component mea-
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-
stream or through a digital to analog converter is the basic unit
tions and transformations are applicable to orthogonal arrays.
of measurement for a sonic anemometer.
References (4), (5), and (6) provide information on common
7.2 Select a sampling period of sufficient duration to obtain
non-orthogonal arrays. Obtain specific calculations and trans-
statistically stable measurements of the phenomena of interest.
formation equations from the manufacturer.
Sampling periods of at least 10 min duration usually generate
9.2 Fig. 1 illustrates a coordinate system applicable to
sufficient data to describe the turbulent state of the atmosphere
orthogonal array sonic anemometers. The usual wind compo-
during steady wind conditions. Sampling periods in excess of
nent sign convention is as follows:
1 h may contain undesired trends in wind direction.
9.2.1 An along-axis wind component entering the array
from the front will have a positive sign (+u ).
8. Procedure
si
9.2.2 A cross-axis wind component entering the array from
8.1 Perform system calibration in a zero wind chamber
the left will have a positive sign (+v ).
(refer to the manufacturer’s instructions). si
9.2.3 A vertical wind component entering the array from the
8.2 Mount the instrument array on a solid, vibration-free
bottom will have a positive sign (+w ).
platform
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