ASTM D5741-96(2007)e1
(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
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. 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 2007)
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.
´ NOTE—Editorially added the term “degrees” to subection 4.1.3 in October 2007.
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 characteris-
three-second and peak one-minute speeds, and standard devia- tic 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
1.2 This practice may be used with other kinds of sensors if profile validity, would predict the wind speed would become
the response characteristics of the sensors, including their zero (1). It can be estimated for direction sectors from a
signal conditioners, are equivalent or faster and the measure- landscape description.
ment uncertainty of the system is equivalent or better than 3.1.2 damped natural wavelength (l , m)—a characteristic
d
those specified below. ofawindvaneempiricallyrelatedtothedelaydistanceandthe
1.3 The characterization prescribed in this practice will damping ratio. See Test Method D5366 for test methods to
provide information on wind acceptable for a wide variety of determine the delay distance and equations to estimate the
applications. damped natural wavelength.
3.1.3 damping ratio (h, 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
Oct. 29–30, 1992. response where no overshoot occurs. See Test Method D5366
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
3.1.4 distance constant (L, m)—the distance the air flows
responsibility of the user of this standard to establish appro-
past a rotating anemometer during the time it takes the cup
priate safety and health practices and determine the applica-
wheelorpropellertoreach(1−1/e)or63%oftheequilibrium
bility of regulatory limitations prior to use.
speed after a step change in wind speed. See Test Method
2. Referenced Documents D5096.
2 3.1.5 maximum operating speed (u , m/s)—as related to
m
2.1 ASTM Standards:
anemometer,thehighestspeedaswhichthesensorwillsurvive
D1356 Terminology Relating to Sampling and Analysis of
the force of the wind and perform within the accuracy
Atmospheres
specification.
D5096 Test Method for Determining the Performance of a
3.1.6 maximum operating speed (u , m/s)—as related to
m
Cup Anemometer or Propeller Anemometer
wind vane, the highest speed at which the sensor will survive
D5366 Test Method for Determining the Dynamic Perfor-
the force of the wind and perform within the accuracy
mance of a Wind Vane
specification.
3.1.7 standard deviation of wind direction (s , degrees)—
u
ThispracticeisunderthejurisdictionofASTMCommitteeD22onAirQuality
the unbiased estimate of the standard deviation of wind
and is the direct responsibility of Subcommittee D22.11 on Meteorology.
direction samples about the mean horizontal wind direction.
Current edition approved Oct. 1, 2007. Published December 2007. Originally
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The circular scale of wind direction with a discontinuity at
approved in 1996. Last previous edition approved in 2002 as D5741-96(2002) .
DOI: 10.1520/D5741-96R07E01.
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.
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D5741–96 (2007)
north may bias the calculation when the direction oscillates 4.1.1 The wind sensor location will be identified by an
about north. Estimates of the standard deviation such as unambiguous label which will include either the longitude and
suggested by (2, 3) are acceptable.
latitude with a resolution of1sofarc (about 30 m or less) or
3.1.8 standard deviation of wind speed (s , m/s)—the
a station number which will lead to that information in the
u
estimateofthestandarddeviationofwindspeedsamplesabout
station description file. When redundant sensors or microscale
the mean wind speed.
network stations (for example, airport runway sensors) are
3.1.9 starting threshold (u , m/s)—as related to anemom-
available, they will have individual labels which unambigu-
eter, the lowest speed at which the sensor begins to turn and
ously identify the data they produce.
continues to turn and produces a measurable signal when
4.1.2 The anemometer and wind vane shall be located at a
mounted in its normal position (see Test Method D5096).
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,
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 (u, degrees)—the direction, refer-
a solitary mast. If side mounting is necessary, the boom length
enced to true north, from which air flows past the sensor
shouldbeatleastthreetimesthemastwidth.Intheundesirable
location if the sensor or other obstructions were absent. The
wind direction distribution is characterized over each 10-min case that locally no open terrain is available and the measure-
period with a scalar (non-speed weighted) mean, standard ment is to be made above some building, then the wind sensor
deviation, and the direction of the peak 1-min average speed.
heightabovetherooftopshouldbeatleast1.5timesthelesser
The circular direction range, with its discontinuity at north,
of the maximum building height and the maximum horizontal
requires special attention in the averaging process. A unit
dimension of the major roof surface. In this case, the station
vector method is an acceptable solution to this problem.
description file shall indicate the height above ground level
3.1.12.1 Discussion—Wind vane direction systems provide
(AGL) of the highest part of the building, the height of the
outputswhenthewindspeedisbelowthestartingthresholdfor
wind sensors above ground, AGL, and the height of the wind
thevane.Forthispractice,reportthecalculatedvalues(see4.3
sensors above roof level. Site characteristics shall be docu-
or4.4)whenmorethan25%ofthepossiblesamplesareabove
mented in sectors no greater than 45 degrees nor smaller than
the wind vane threshold and the standard deviation of the
30 degrees in width around the wind sensors. The near terrain
acceptable samples, s , is 30° or less, otherwise report light
u
may be characterized with photographs, taken at wind sensor
and variable code, 000.
height if possible, aimed radially outward at labeled central
3.1.13 wind speed (u, m/s)—the speed with which air flows
angles, with respect to true north. Average roughness of the
pastthesensorlocationifthesensororotherobstructionswere
nearest 3 km of each sector shall be characterized according to
absent. The wind speed distribution is characterized over each
the roughness class as tabulated above (4). The z numbers in
10-minperiodwithascalarmean,standarddeviation,peak3-s
Table 1 are typical and not precise statements.
average, and peak 1-min average.
4.1.4 Importantterrainfeaturesatdistanceslargerthan3km
3.2 For definitions of additional terms used in this practice,
(hills, cities, lakes, and so forth, within 20 km) shall be
refer to Terminology D1356.
identified by sector and distance.Additional information, such
4. Summary of Practice
as aerial photographs, maps, and so forth, pertinent to the site,
4.1 Siting of the Wind Sensors: is recommended to be added to the basic site documentation.
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.
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D5741–96 (2007)
NOTE 2—Cameras using 35-mm film in the landscape orientation will NOTE 5—Asample of the wind direction may be used ONLYwhen the
have the following theoretical focal length to field angle relationships: sample of wind speed is at or above the wind direction starting threshold.
50 mm yields 40°
4.3 Standard Data Output forArchives—Timelabelsshould
40 mm yields 48°
28 mm yields 66° use the ending time of the interval. If a different labeling
method is consistently used, it must be defined. The data
Printsortransparenciesmaynotutilizethetotaltheoreticalwidthofthe
outputs are listed as follows:
image. It is desirable to label known angles in the photograph. For
4.3.1 Ten-minute scalar averaged wind speed.
example, a 45° sector photograph could have a central label of 360 with
marker flags located at 337.5° and 022.5° true.
4.3.2 Ten-minute unit vector or scalar averaged wind direc-
tion.
4.2 Characteristics of the Wind Systems—There are two
4.3.3 Fastest 3-s gust during the 10-min period.
categories of sensor design within this practice. Sensitive
4.3.4 Time of the fastest 3-s gust during the 10-min period.
describes sensors commonly applied for all but extreme wind
4.3.5 Fastest 1-min scalar averaged wind speed during the
conditions. Ruggedized describes sensors intended to function
10-min period (fastest minute).
during extreme wind conditions. The application of this prac-
4.3.6 Average wind direction for the fastest 1-min wind
tice requires the starting threshold (u ) of both the wind vane
speed.
and the anemometer to meet the same operating range cat-
4.3.7 Standard deviation of the wind speed samples (1 to 3
egory.
s) about the 10-min mean speed (s ).
u
4.2.1 Operating Range:
4.3.8 Standarddeviationofthewinddirectionsamples(1to
3 s) about the 10-min mean direction (s ).
u
Category Starting Threshold, u Maximum Speed, u
0 m
4.4 Optional Condensed Data Output for Archives—Some
Sensitive 0.5 m/s 50 m/s networks will not be able to save eight 10-min data sets (48
Ruggedized 1.0 m/s 90 m/s
values plus time and identification) each hour. For those cases,
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
circuitry. 4.4.5 Fastest 1-min scalar averaged wind speed during the
60-min period.
Anemometer Distance constant, L <5 m
Wind vane Damping ratio, h >0.3
4.4.6 Average wind direction for the fastest 1-min wind
Wind vane Damped natural wavelength, l <10 m
d
speed.
4.2.3 Measurement Uncertainty: 4.4.7 Ending time of the fastest 1-min wind speed.
4.4.8 Root-mean-square of six 10-min standard deviations
of the wind speed samples about their 10-min mean speeds.
Wind speed Between 0.5 (or 1) and 10 m/s 60.5 m/s
Wind speed >10 m/s 5 % of reading
4.4.9 Root-mean-square of six 10-min standard deviations
Wind direction Degrees of arc to true north 65° (see Note 5)
of the wind direction samples about their 10-min mean
NOTE 3—The relative accuracy of the position of the vane with respect
directions.
tothesensorbaseshouldbelessthan 63°foraveragedsamples.Thebias
4.5 Nonstandard Data Outputs for
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