ASTM D5741-96(2002)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
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.
Note1—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 2002)
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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Editorially added a new Reference item in October 2002.
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 andAnalysis 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
This practice is under the jurisdiction of ASTM Committee D22 on Sampling the unbiased estimate of the standard deviation of wind
and Analysis of Atmospheres and is the direct responsibility of Subcommittee
direction samples about the mean horizontal wind direction.
D22.11 on Meteorology.
The circular scale of wind direction with a discontinuity at
Current edition approved May 10, 1996. Published July 1996.
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 (2002)
north may bias the calculation when the direction oscillates latitude with a resolution of1sofarc (about 30 m or less) or
about north. Estimates of the standard deviation such as a station number which will lead to that information in the
suggested by (2, 3) are acceptable. station description file. When redundant sensors or microscale
3.1.8 standard deviation of wind speed (s , m/s)—the network stations (for example, airport runway sensors) are
u
estimateofthestandarddeviationofwindspeedsamplesabout available, they will have individual labels which unambigu-
the mean wind speed. ously identify the data they produce.
3.1.9 starting threshold (u , m/s)—as related to anemom-
0 4.1.2 The anemometer and wind vane shall be located at a
eter, the lowest speed at which the sensor begins to turn and
10-m height above level or gently sloping terrain with an open
continues to turn and produces a measurable signal when
fetch of at least 150 m in all directions, with the largest fetch
mounted in its normal position (see Test Method D5096).
possible in the prevailing wind direction. Compromise is
3.1.10 starting threshold(u ,m/s)—as related to system,the
0 frequently recognized and acceptable for some sites. Obstacles
indicated wind speed when the anemometer is at rest.
in the vicinity should be at least ten times their own height
3.1.11 starting threshold(u ,m/s)—as related to wind vane,
0 distant from the wind sensors.
the lowest speed at which the vane can be observed or
4.1.3 Thewindsensorsshallpreferablybelocatedontopof
measured moving from a 10° offset position in a wind tunnel
a solitary mast. If side mounting is necessary, the boom length
(see Test Method D5366).
shouldbeatleastthreetimesthemastwidth.Intheundesirable
3.1.12 wind direction (u, degrees)—the direction, refer-
case that locally no open terrain is available and the measure-
enced to true north, from which air flows past the sensor
ment is to be made above some building, then the wind sensor
location if the sensor or other obstructions were absent. The
heightabovetherooftopshouldbeatleast1.5timesthelesser
wind direction distribution is characterized over each 10-min
of the maximum building height and the maximum horizontal
period with a scalar (non-speed weighted) mean, standard
dimension of the major roof surface. In this case, the station
deviation, and the direction of the peak 1-min average speed.
description file shall indicate the height above ground level
The circular direction range, with its discontinuity at north,
(AGL) of the highest part of the building, the height of the
requires special attention in the averaging process. A unit
wind sensors above ground, AGL, and the height of the wind
vector method is an acceptable solution to this problem.
sensors above roof level. Site characteristics shall be docu-
3.1.12.1 Discussion—Wind vane direction systems provide
mented in sectors no greater than 45 nor smaller than 30 in
outputswhenthewindspeedisbelowthestartingthresholdfor
width around the wind sensors. The near terrain may be
thevane.Forthispractice,reportthecalculatedvalues(see4.3
characterized with photographs, taken at wind sensor height if
or4.4)whenmorethan25%ofthepossiblesamplesareabove
possible,aimedradiallyoutwardatlabeledcentralangles,with
the wind vane threshold and the standard deviation of the
respecttotruenorth.Averageroughnessofthenearest3kmof
acceptable samples, s , is 30° or less, otherwise report light
u
each sector shall be characterized according to the roughness
and variable code, 000.
class as tabulated above (4). The z numbers in Table 1 are
3.1.13 wind speed (u, m/s)—the speed with which air flows
typical and not precise statements.
pastthesensorlocationifthesensororotherobstructionswere
4.1.4 Importantterrainfeaturesatdistanceslargerthan3km
absent. The wind speed distribution is characterized over each
(hills, cities, lakes, and so forth, within 20 km) shall be
10-minperiodwithascalarmean,standarddeviation,peak3-s
identified by sector and distance.Additional information, such
average, and peak 1-min average.
as aerial photographs, maps, and so forth, pertinent to the site,
3.2 For definitions of additional terms used in this practice,
is recommended to be added to the basic site documentation.
refer to Terminology D1356.
NOTE 2—Cameras using 35-mm film in the landscape orientation will
4. Summary of Practice
have the following theoretical focal length to field angle relationships:
4.1 Siting of the Wind Sensors:
50 mm yields 40°
4.1.1 The wind sensor location will be identified by an 40 mm yields 48°
28 mm yields 66°
unambiguous label which will include either the longitude and
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 (2002)
Printsortransparenciesmaynotutilizethetotaltheoreticalwidthofthe
method is consistently used, it must be defined. The data
image. It is desirable to label known angles in the photograph. For
outputs are listed as follows:
example, a 45° sector photograph could have a central label of 360 with
4.3.1 Ten-minute scalar averaged wind speed.
marker flags located at 337.5° and 022.5° true.
4.3.2 Ten-minute unit vector or scalar averaged wind direc-
4.2 Characteristics of the Wind Systems—There are two
tion.
categories of sensor design within this practice. Sensitive
4.3.3 Fastest 3-s gust during the 10-min period.
describes sensors commonly applied for all but extreme wind
4.3.4 Time of the fastest 3-s gust during the 10-min period.
conditions. Ruggedized describes sensors intended to function
4.3.5 Fastest 1-min scalar averaged wind speed during the
during extreme wind conditions. The application of this prac-
10-min period (fastest minute).
tice requires the starting threshold (u ) of both the wind vane
4.3.6 Average wind direction for the fastest 1-min wind
and the anemometer to meet the same operating range cat-
speed.
egory.
4.3.7 Standard deviation of the wind speed samples (1 to 3
4.2.1 Operating Range:
s) about the 10-min mean speed (s ).
u
4.3.8 Standarddeviationofthewinddirectionsamples(1to
Category Starting Threshold, u Maximum Speed, u
0 m
3 s) about the 10-min mean direction (s ).
u
Sensitive 0.5 m/s 50 m/s
4.4 Optional Condensed Data Output for Archives—Some
Ruggedized 1.0 m/s 90 m/s
networks will not be able to save eight 10-min data sets (48
4.2.2 Dynamic Response Characteristics—Dynamic re-
values plus time and identification) each hour. For those cases,
sponse characteristics of the measurement system may include
an abbreviated or condensed alternative is provided. When the
both the sensor response and a measurement circuit contribu-
condensed output is employed the following outputs are
tion. The specified values are for the entire measurement
required.
system, including sensors and signal conditioners (5).Itis
4.4.1 Sixty-minute scalar averaged wind speed.
expected that the characteristics of the sensors, which can be
4.4.2 Sixty-minute unit vector or scalar averaged wind
independently determined by the referenced Test Methods
direction.
D5096 and D5366, will not be measurably altered by the
4.4.3 Fastest 3-s gust during the 60-min period.
circuitry.
4.4.4 Wind direction for the fastest 3-s gust.
Anemometer Distance constant, L <5 m
Wind vane Damping ratio, h >0.3 4.4.5 Fastest 1-min scalar averaged wind speed during the
Wind vane Damped natural wavelength, l <10 m
d
60-min period.
4.4.6 Average wind direction for the fastest 1-min wind
4.2.3 Measurement Uncertainty:
speed.
Wind speed Between 0.5 (or 1) and 10 m/s 60.5 m/s 4.4.7 Ending time of the fastest 1-min wind speed.
Wind speed >10 m/s 5 % of reading
4.4.8 Root-mean-square of six 10-min standard deviations
Wind direction Degrees of arc to true north 65° (see Note 5)
of the wind speed samples about their 10-min mean speeds.
NOTE 3—The relative accuracy of the position of the vane with respect
4.4.9 Root-mean-square of six 10-min standard deviations
tothesensorbaseshouldbelessthan 63°foraveragedsamples.Thebias
of the wind direction samples about their 10-min mean
of the sensor base alignment to true north should be less than 62°.
directions.
4.2.4 Measurement Resolution:
4.5 Nonstandard Data Outputs for Archives—When some,
Average Standard De-
but not all, of the required outputs are reported from a station
viation
which meets all of the measurement and sensor performance
Wind speed 0.1 m/s 0.1 m/s specifications, they may be reported as conforming to the
Wind direction 1° 0.1°
standard with
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