In this document, We discuss about different methods of wind measurement

1. Wind Measurement
ATS409:Instrumentations in Atmospheric Studies
Submitted by:
Manu Jangid
2023MSATS012
Submitted to:
Dr. Chinmay Mallik
Assistant Professor
CIA-II PRESENTATION
Department of Atmospheric Science
School of Earth Sciences
Central University of Rajasthan

2. Introduction and Learning Objectives
Winds Fundamentals
Categories of Wind Sensors
The Cup Anemometer
Advantages and Limitations
References

3. Introduction and Learning Objectives
• Wind is the motion of air relative to Earth.
• Wind is a vector quantity with direction and speed, so multiple measurements are required to determine
the components of the vector in two or three dimensions
• Like all measurements, an observation of the wind should include appropriate “provenance”
SOURCE-Meted
 The map shows several local wind systems from around the world
• The normal unit of wind speed is the knot (nautical
mile per hour = 0.51 m/s = 1.15 mph).
• Wind direction is measured relative to true north (not
magnetic north) and is reported from where the wind is
blowing.
• An easterly wind blows from the east or 90 degrees, a
southerly from the south or 180 degrees and a westerly
from the west or 270 degrees.

4. Winds Fundamentals • Temperature, pressure, and wind are causally linked, so measurements of all three are often
needed to study the wind fields and especially dynamic changes in those fields.
• For example, the map shows the relationship between wind and pressure at a global scale
SOURCE-Meted

5. 1. Wind passage (L (m)): The distance that wind (air mass) covers over a given period of time (t).
2. Instantaneous wind speed (Vi (m/s)): Wind speeds change very quickly
3. Average wind speed (Vm (m/s)): The average wind speed is the average of the instantaneous wind speed over
a ten-minute period
4. Starting threshold speed (V0 (m/s)): The lowest wind speed at which a rotating anemometer mounted in its
normal position starts to turn continuously.
Units
Speed conversion table Wind-direction scale
 In synoptic reports, the average wind speed measured over a period of 10 minutes is reported every 0.5 m/s or
in knots (kt) and , the average wind direction in degrees to the nearest 10 degrees using a code number from
01 to 36.

6. Wind Estimation Beaufort Scale

7. Categories of Wind Sensors
S.N. Category Example(s) Common Uses
1 Mechanical sensors cup or propeller anemometer; wind
vane
measurements at weather stations
(official and home)
2 In situ electronic sensors hot-wire anemometer fast response measurements;
turbulence characterization
3 Drifting-position sensors radiosonde, driftsonde, pibal atmospheric soundings
4 Sensors based on impact
pressure
pitot tube measuring airspeed of moving
vehicles including aircraft
5 Sensors that use
measurements of a time
shift
ultrasonic anemometer modern official weather stations;
research that investigates
turbulence or fluxes
6 Sensors that use
measurements of a Doppler
shift
Doppler radar and lidar; wind
profiler
remote measurement of wind at a
range of positions from the
sensor
The instruments used to measure wind are known as Anemometers.

8. The Cup Anemometer
SOURCE-Meted
 The cup anemometer provides the wind speed and the vane
provides the wind direction
• The current accepted standard cup anemometer has three cups.
• The cup anemometer is similar to a first-order system that has an
exponential response to changes in wind speed, while the wind
vane resembles a second-order system with a dynamic response
toward an equilibrium position with damping.
The important characteristics of cup anemometers
1. Linear calibration: Cup anemometers are calibrated under
steady conditions in a wind tunnel
 Typical calibrations are linear; v = aω + b
where v=wind speed ,ω=angular rotation rate, a&b= calibration
coefficients
 There is also a “starting threshold” for v (typically <0.3 m/s)
below which the cups do not rotate. Typical values are a=0.4 m
and b=0.2 m/s
 The NCAR Earth
Observing Laboratory
wind tunnel,
specifically designed
for testing
meteorological
instrumentation.

9. 2. Response time: Although the cup anemometer
responds exponentially to a change in the wind, the
time constant varies with the magnitude of the wind
3. Overspeeding: The cup anemometer responds faster
to increases in wind speed than to decreases, which results
in a bias error in the average wind called “overspeeding.
 The green line (v) is the
assumed wind speed and
the blue line (M) is the
modeled measurement,
responding faster to an
increase in v than to a
decrease.
SOURCE-Meted

10. The Wind Vane:
 Wind vanes typically provide uncertainty of <3°, and like cup anemometers are characterized by a
distance constant called the delay distance (typically about 1 m; Finkelstein, 1981) that specifies the air
motion required to give 50% response to a wind direction change of 10°.

11. Advantages and Limitations
 The biggest disadvantage of mechanical anemometers is that the
bearings have to be replaced on a routine basis.
 In addition, whether cup or propeller, they have a minimum
starting threshold and both exhibit some non-linearity, albeit not
much.
 Response time is longer/slower than other anemometers, including
hot-wire and sonic anemometers.
SOURCE-Meted
 Exploded view of cup anemometer with 3D -printed parts

12. REFERENCES
 https://www.meted.ucar.edu/index.php
 https://www.metoffice.gov.uk/weather/guides/observations/how-we-measure-
wind
 https://www.jma.go.jp/jma/jma-eng/jma
center/ric/Our%20activities/International/CP4-Wind.pdf