ASTM D5741-96(2011)
(Practice)Standard Practice for Characterizing Surface Wind Using a Wind Vane and Rotating Anemometer
Standard Practice for Characterizing Surface Wind Using a Wind Vane and Rotating Anemometer
SIGNIFICANCE AND USE
This practice will characterize the distribution of wind with a maximum of utility and a minimum of archive space. Applications of wind data to the fields of air quality, wind engineering, wind energy, agriculture, oceanography, forecasting, aviation, climatology, severe storms, turbulence and diffusion, military, and electrical utilities are satisfied with this practice. When this practice is employed, archive data will be of value to any of these fields of application. The consensus reached for this practice includes representatives of instrument manufacturers which provides a practical acceptance of these theoretical principles used to characterize the wind.
SCOPE
1.1 This practice covers a method for characterizing surface wind speed, wind direction, peak one-minute speeds, peak three-second and peak one-minute speeds, and standard deviations of fluctuation about the means of speed and direction.
1.2 This practice may be used with other kinds of sensors if the response characteristics of the sensors, including their signal conditioners, are equivalent or faster and the measurement uncertainty of the system is equivalent or better than those specified below.
1.3 The characterization prescribed in this practice will provide information on wind acceptable for a wide variety of applications.
Note 1—This practice builds on a consensus reached by the attendees at a workshop sponsored by the Office of the Federal Coordinator for Meteorological Services and Supporting Research in Rockville, MD on Oct. 29–30, 1992.
1.4 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: D5741 − 96 (Reapproved 2011)
Standard Practice for
Characterizing Surface Wind Using a Wind Vane and
Rotating Anemometer
This standard is issued under the fixed designation D5741; 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 Thispracticecoversamethodforcharacterizingsurface 3.1 Definitions of Terms Specific to This Standard:
wind speed, wind direction, peak one-minute speeds, peak 3.1.1 aerodynamic roughness length (z , m )—a character-
three-second and peak one-minute speeds, and standard devia- istic length representing the height above the surface where
tions of fluctuation about the means of speed and direction. extrapolation of wind speed measurements, below the limit of
profile validity, would predict the wind speed would become
1.2 This practice may be used with other kinds of sensors if
zero (1). It can be estimated for direction sectors from a
the response characteristics of the sensors, including their
landscape description.
signal conditioners, are equivalent or faster and the measure-
3.1.2 damped natural wavelength (λ , m)—a characteristic
ment uncertainty of the system is equivalent or better than
d
ofawindvaneempiricallyrelatedtothedelaydistanceandthe
those specified below.
damping ratio. See Test Method D5366 for test methods to
1.3 The characterization prescribed in this practice will
determine the delay distance and equations to estimate the
provide information on wind acceptable for a wide variety of
damped natural wavelength.
applications.
3.1.3 damping ratio (η, dimensionless)—the ratio of the
NOTE 1—This practice builds on a consensus reached by the attendees
actualdamping,relatedtotheinertial-drivenovershootofwind
at a workshop sponsored by the Office of the Federal Coordinator for
vanes to direction changes, to the critical damping, the fastest
Meteorological Services and Supporting Research in Rockville, MD on
response where no overshoot occurs. See Test Method D5366
Oct. 29–30, 1992.
for test methods and equations to determine the damping ratio
1.4 This standard does not purport to address all of the
of a wind vane.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 3.1.4 distance constant (L, m)—the distance the air flows
priate safety and health practices and determine the applica- past a rotating anemometer during the time it takes the cup
bility of regulatory limitations prior to use. wheel or propeller to reach (1−1⁄e) or 63% of the equilib-
riumspeedafterastepchangeinwindspeed.SeeTestMethod
2. Referenced Documents
D5096.
2.1 ASTM Standards:
3.1.5 maximum operating speed (u , m/s)—as related to
m
D1356Terminology Relating to Sampling and Analysis of
anemometer,thehighestspeedaswhichthesensorwillsurvive
Atmospheres
the force of the wind and perform within the accuracy
D5096Test Method for Determining the Performance of a
specification.
Cup Anemometer or Propeller Anemometer
3.1.6 maximum operating speed (u , m/s)—as related to
m
D5366Test Method for Determining the Dynamic Perfor-
wind vane, the highest speed at which the sensor will survive
mance of a Wind Vane
the force of the wind and perform within the accuracy
specification.
3.1.7 standard deviation of wind direction (σ , degrees)—
θ
the unbiased estimate of the standard deviation of wind
ThispracticeisunderthejurisdictionofASTMCommitteeD22onAirQuality
direction samples about the mean horizontal wind direction.
and is the direct responsibility of Subcommittee D22.11 on Meteorology.
The circular scale of wind direction with a discontinuity at
Current edition approved Oct. 1, 2011. Published October 2011. Originally
north may bias the calculation when the direction oscillates
approved in 1996. Last previous edition approved in 2007 as D5741-96(2007).
DOI: 10.1520/D5741-96R11.
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 boldface numbers in parentheses refers to the list of references at the end
the ASTM website. of this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5741 − 96 (2011)
about north. Estimates of the standard deviation such as 4.1.1 The wind sensor location will be identified by an
suggested by (2, 3) are acceptable. unambiguous label which will include either the longitude and
latitude with a resolution of1sofarc (about 30 m or less) or
3.1.8 standard deviation of wind speed (σ , m/s)—the esti-
u
a station number which will lead to that information in the
mateofthestandarddeviationofwindspeedsamplesaboutthe
station description file. When redundant sensors or microscale
mean wind speed.
network stations (for example, airport runway sensors) are
3.1.9 starting threshold (u , m/s)—as related to
available, they will have individual labels which unambigu-
anemometer, the lowest speed at which the sensor begins to
ously identify the data they produce.
turn and continues to turn and produces a measurable signal
4.1.2 The anemometer and wind vane shall be located at a
whenmountedinitsnormalposition(seeTestMethodD5096).
10-m height above level or gently sloping terrain with an open
3.1.10 starting threshold(u ,m/s)—as related to system,the
fetch of at least 150 m in all directions, with the largest fetch
indicated wind speed when the anemometer is at rest.
possible in the prevailing wind direction. Compromise is
3.1.11 starting threshold(u ,m/s)—as related to wind vane,
0 frequently recognized and acceptable for some sites. Obstacles
the lowest speed at which the vane can be observed or
in the vicinity should be at least ten times their own height
measured moving from a 10° offset position in a wind tunnel
distant from the wind sensors.
(see Test Method D5366).
4.1.3 Thewindsensorsshallpreferablybelocatedontopof
3.1.12 wind direction (θ,degrees)—thedirection,referenced
a solitary mast. If side mounting is necessary, the boom length
to true north, from which air flows past the sensor location if
shouldbeatleastthreetimesthemastwidth.Intheundesirable
the sensor or other obstructions were absent. The wind direc-
case that locally no open terrain is available and the measure-
tion distribution is characterized over each 10-min period with
ment is to be made above some building, then the wind sensor
a scalar (non-speed weighted) mean, standard deviation, and
heightabovetherooftopshouldbeatleast1.5timesthelesser
the direction of the peak 1-min average speed. The circular
of the maximum building height and the maximum horizontal
direction range, with its discontinuity at north, requires special
dimension of the major roof surface. In this case, the station
attention in the averaging process. A unit vector method is an
description file shall indicate the height above ground level
acceptable solution to this problem.
(AGL) of the highest part of the building, the height of the
3.1.12.1 Discussion—Wind vane direction systems provide
wind sensors above ground, AGL, and the height of the wind
outputswhenthewindspeedisbelowthestartingthresholdfor
sensors above roof level. Site characteristics shall be docu-
thevane.Forthispractice,reportthecalculatedvalues(see4.3
mented in sectors no greater than 45 degrees nor smaller than
or4.4)whenmorethan25%ofthepossiblesamplesareabove
30 degrees in width around the wind sensors. The near terrain
the wind vane threshold and the standard deviation of the
may be characterized with photographs, taken at wind sensor
acceptable samples, σ , is 30° or less, otherwise report light
height if possible, aimed radially outward at labeled central
θ
and variable code, 000.
angles, with respect to true north. Average roughness of the
nearest 3 km of each sector shall be characterized according to
3.1.13 wind speed (u, m/s)—the speed with which air flows
the roughness class as tabulated above (4). The z numbers in
pastthesensorlocationifthesensororotherobstructionswere
Table 1 are typical and not precise statements.
absent. The wind speed distribution is characterized over each
10-minperiodwithascalarmean,standarddeviation,peak3-s
4.1.4 Importantterrainfeaturesatdistanceslargerthan3km
average, and peak 1-min average. (hills, cities, lakes, and so forth, within 20 km) shall be
identified by sector and distance.Additional information, such
3.2 For definitions of additional terms used in this practice,
as aerial photographs, maps, and so forth, pertinent to the site,
refer to Terminology D1356.
is recommended to be added to the basic site documentation.
4. Summary of Practice
NOTE 2—Cameras using 35-mm film in the landscape orientation will
4.1 Siting of the Wind Sensors: have the following theoretical focal length to field angle relationships:
TABLE 1 Characterizations Extracted from Wieringa, J. (4)
No. z , m Landscape Description
1: 0.0002 Sea Open sea or lake (irrespective of the wave size), tidal flat, snow-covered flat plain, featureless desert, tarmac and concrete, with a
free fetch of several kilometres.
2: 0.005 Smooth Featureless land surface without any noticeable obstacles and with negligible vegetation; for example, beaches, pack ice without
large ridges, morass, and snow-covered or fallow open country.
3: 0.03 Open Level country with low vegetation (for example, grass) and isolated obstacles with separations of at least 50 obstacle heights; for
example, grazing land without windbreaks, heather, moor and tundra, runway area of airports.
4: 0.10 Roughly open Cultivated area with regular cover of low crops, or moderately open country with occasional obstacles (for example, low hedges,
single rows of trees, isolated farms) at relative horizontal distances of at least 20 obstacle heights.
5: 0.25 Rough Recently developed young landscape with high crops or crops of varying heights, and scattered obstacles (for example, dense
shelter-belts, vineyards) at relative distances of about 15 obstacle heights.
6: 0.5 Very rough Old cultivated landscape with many rather large obstacle groups (large farms, clumps of forest) separated by open spaces of about
10 obstacle heights. Also low-large vegetation with small interspaces, such as bushland, orchards, young densely planted forest.
7: 1.0 Closed Landscape totally and quite regularly covered with similar-size large obstacles, with open spaces comparable to the obstacle heights;
for example, mature regular forests, homogeneous cities, or villages.
8: >2 Chaotic Centers of large towns with mixture of low-rise and high-rise buildings. Also irregular large forests with many clearings.
D5741 − 96 (2011)
method is consistently used, it must be defined. The data
50 mm yields 40°
40 mm yields 48°
outputs are listed as follows:
28 mm yields 66°
4.3.1 Ten-minute scalar averaged wind speed.
Printsortransparenciesmaynotutilizethetotaltheoreticalwidthofthe 4.3.2 Ten-minute unit vector or scalar averaged wind direc-
image. It is desirable to label known angles in the photograph. For
tion.
example, a 45° sector photograph could have a central label of 360 with
4.3.3 Fastest 3-s gust during the 10-min period.
marker flags located at 337.5° and 022.5° true.
4.3.4 Time of the fastest 3-s gust during the 10-min period.
4.2 Characteristics of the Wind Systems—There are two
4.3.5 Fastest 1-min scalar averaged wind speed during the
categories of sensor design within this practice. Sensitive
10-min period (fastest minute).
describes sensors commonly applied for all but extreme wind
4.3.6 Average wind direction for the fastest 1-min wind
conditions. Ruggedized describes sensors intended to function
speed.
during extreme wind conditions. The application of this prac-
4.3.7 Standard deviation of the wind speed samples (1 to 3
tice requires the starting threshold (u ) of both the wind vane
s) about the 10-min mean speed (σ ).
u
and the anemometer to meet the same operating range cat-
4.3.8 Standarddeviationofthewinddirectionsamples(1to
egory.
3 s) about the 10-min mean direction (σ ).
θ
4.2.1 Operating Range:
4.4 Optional Condensed Data Output for Archives—Some
Category Starting Threshold, u Maximum Speed, u
0 m
networks will not be able to save eight 10-min data sets (48
Sensitive 0.5 m/s 50 m/s
values plus time and identification) each hour. For those cases,
Ruggedized 1.0 m/s 90 m/s
an abbreviated or condensed alternative is provided. When the
4.2.2 Dynamic Response Characteristics—Dynamic re-
condensed output is employed the following outputs are
sponse characteristics of the measurement system may include
required.
both the sensor response and a measurement circuit contribu-
4.4.1 Sixty-minute scalar averaged wind speed.
tion. The specified values are for the entire measurement
4.4.2 Sixty-minute unit vector or scalar averaged wind
system, including sensors and signal conditioners (5).Itis
direction.
expected that the characteristics of the sensors, which can be
4.4.3 Fastest 3-s gust during the 60-min period.
independently determined by the referenced Test Methods
4.4.4 Wind direction for the fastest 3-s gust.
D5096 and D5366, will not be measurably altered by the
4.4.5 Fastest 1-min scalar averaged wind speed during the
circuitry.
60-min period.
Anemometer Distance constant, L <5 m
Wind vane Damping ratio, η >0.3 4.4.6 Average wind direction for the fastest 1-min wind
Wind vane Damped natural wavelength, λ <10 m
d
speed.
4.2.3 Measurement Uncertainty: 4.4.7 Ending time of the fastest 1-min wind speed.
Wind speed Between 0.5 (or 1) and 10 m/s ±0.5 m/s 4.4.8 Root-mean-square of six 10-min standard deviations
Wind speed >10 m/s 5 % of reading
of the wind speed samples about their 10-min mean speeds.
Wind direction Degrees of arc to true north ±5° (see Note 5)
4.4.9 Root-mean-square of six 10-min standard deviations
NOTE 3—The relative accuracy of the position of the vane with respect
of the wind direction samples about their 10-min mean
to the sensor base should be less than 63° for averaged samples.The bias
directions.
of the sensor base alignment to true north should be less than 62°.
4.5 Nonstandard Data Outputs for Archives—When some,
4.2.4 Measurement Resolution:
but not all, of the required outputs are reported from a station
Average Standard
which meets all of the measurement and sensor performance
Deviation
specifications, they may be reported as conforming to the
Wind speed 0.1 m/s 0.1
...
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