1. Wind Measurements Local right-hand Cartesian coordinateUp
North y V x U O
East O
Polar coordinate

2. Conversion to speed and direction
Conversion to U and V

3. Dynamic force anemometers
Unites of wind speeds
m/s, mile/h, km/h, knot, …
Wind sensors
There are three classes of instruments:
1. dynamic force anemometers
2. pressure pulse frequency anemometers
3. thermal anemometers
Dynamic force anemometers
cup anemometers, vane windmill, and gill-type anemometers
Drives an electrical generator
Threshold

4. Cup anemometer
Vane windmill
Gill-type
anemometer

5. Four Cup anemometer It was invented (1846) by
Dr. John Thomas Romney Robinson
But he wrongly claimed that no matter
how big the cups or how long the arms,
the cups always move with one-third
of the speed of the wind.
Anemometer factor :
the actual relationship between the
speed of the wind and that of the cups.
It depends on the dimensions of the cups and arms

6. Three Cup anemometer Three cup anemometer was developed
by the Canadian John Patterson in 1926
Patterson found that each cup produced
maximum torque when it was at 45
degrees to the wind flow. The three cup
anemometer also has a more constant
torque and responds more quickly to
gusts than the four cup anemometer
Wind direction:
1. Australian Derek Weston added a tag to one cup, which causes the
cupwheel speed to increase and decrease as the tag moves alternately
with and against the wind. Wind direction, then, can be calculated
from these cyclical changes in cupwheel speed, while wind speed is
as usual determined from the average cupwheel speed.
2. Add a separate of wind vane for directional readings.

7. Windmill anemometers
For windmill, the axis of
rotation must be parallel
to the direction of the wind
and therefore horizontal.
Furthermore, since the
wind varies in direction
and the axis has to follow
its changes, a wind vane
or some other contrivance
to fulfill the same purpose
must be employed.
The R.M. Young Wind Monitor
It combines a propeller and a tail on the same axis to obtain
accurate and precise wind speed and direction.

8. Gill Propeller Anemometer
Gill Propeller Anemometer utilizes a fast
response helicoid propeller whose rotation
is linearly proportional to air velocity.
However, the propeller responds only to
the component of the air flow which is
parallel to its axis of rotation. For
perpendicular air flow, the propeller
does not rotate. Thus, using three
parallels, one can measure 3-D winds.
The standard expanded polystyrene (EPS)
propeller offers maximum sensitivity at
low wind speeds.
Propeller response as a function of winds approximates the cosine
curve, allowing true wind velocity and direction to be calculated.
The propeller anemometer is especially suited for measuring the
vertical wind component.

9. Pressure pulse frequency anemometers (sonic anemometer )
It measures the variation of speed of sound with wind
The best way to get the wind direction is to measure the
components in all three directions

10. 2-D sonic anemometer
3-D sonic anemometer
The spatial resolution is given by the path length between
transducers, which is typically 10 to 20 cm
Sonic anemometers can take measurements with very fine
temporal resolution, 20 Hz or better, which make them well
suited for turbulence measurements.
Their main disadvantage is the distortion of the flow itself by the
structure supporting the transducers, which requires a correction
based upon wind tunnel measurements to minimize the effect.

11. The transducers are usually made by piezoelectric crystals and completely sealed for rugged outdoor operation. The electronics are all contained within the probe bar. This allows it to be operated as a tower mounted instrument, capable of withstanding hostile environmental conditions. The transducer operation and sonic functions, as well as all computation and transmission of data, are under microprocessor control.
Most sonic anemometer can also measure temperature

12. Thermal anemometers (hot wire anemometers )
It uses a very fine wire (on the order of several micrometers)
electrically heated up to some temperature above the ambient.
Air flowing past the wire has a cooling effect on the wire. As
the electrical resistance of most metals is dependent upon the
temperature of the metal (tungsten is a popular choice for
hot-wires), a relationship can be obtained between the resistance
of the wire and the flow velocity.
CCA (Constant-Current Anemometer)
CVA (Constant-Voltage Anemometer)
CTA (Constant-Temperature Anemometer)

14. Velocity pressure probe
Five-hole pressure probe

15. Seven-hole pressure probe

16. Laser Doppler anemometers
use a beam of light from a
laser. Particulates flowing
along with air molecules
near where the beam exits
reflect, or backscatter, the
light back into a detector,
where it is measured
relative to the original laser
beam. When the particles
are in great motion, they produce a Doppler shift for measuring wind
speed in the laser light, which is used to calculate the speed of the
particles, and therefore the air around the anemometer.

17. Wind profilers
A wind profiler is a type of sensitive Doppler radar that uses
electromagnetic waves or sound waves to detect the wind speed
and direction at various elevations above the ground, up to the
troposphere (i.e., between 8 and 17 km above mean sea level)
Detection of the signal backscattered from refractive
index in-homogeneities in the atmosphere
In clear air the scattering targets are the temperature and
humidity fluctuations produced by turbulent eddies

18. Scattering Mechanism
Scattering from atmospheric targets:
irregularities in the refractive index of the air
hydrometeors, particularly wet ones (rain, melting snow, water coated ice)
Scattering from Non-atmospheric targets:
birds and insects (frequency dependant)
smoke plumes
Interfering signals:
Ground and sea clutter
Aircraft and migrating birds
RFI (depends on frequency band)
RFI: Radio Frequency Interference is generated from spikes/surges
that usually come from - Lightning, man-made electrical equipment
noise and various transmitting equipment.

19. Scattering Mechanism When a pulse encounters a target...
It is scattered in all directions.
Of interest is the signal component
received back at the radar.
This signal is typically much weaker
than the original sent from the
transmitter and is called the "return
signal".
The larger the target, the stronger
the scattered signal.

20. Doppler Shift Doppler Formula: fd = - 2 *Vr / 
Doppler Measurement of wind speed based on the Doppler shift in the received signal:
where Vr is the radial velocity of the scatterers
 is wave length
Examples of Wind Profiler Doppler shift (radial velocity 10m/s)
50MHz, wavelength 6m, Doppler shift 3.34Hz
449MHz, wavelength m, Doppler shift 29.9Hz
1290MHz, wavelength 0.23m, Doppler shift 86Hz

21. Measuring horizontal winds using three beams

22. Typical frequencies used in wind profiling
45-65 MHz
MHz
MHz
MHz
The 915 MHz (33 cm, UHF) profiler measures the wind at low
levels, typically up to 1-3 km above ground level, depending on
atmospheric conditions, especially humidity. The top of the
atmospheric boundary layer marked by the entrainment zone is
very visible because the large humidity and temperature gradient
there cause a large change in index of refraction. The 915 MHz
profiler has fairly small antennas (at most 2x2 or 3x3 m), making
it transportable and less expensive.

23. A VHF wind profiler (50 MHz or 6 m) measures wind profiles
between 2 and 16, occasionally 20 km above the ground level
(AGL), but the antenna occupies 2 soccer fields (100x100m).
The US NOAA operates a network of 400 MHz wind profilers.
These are smaller (antenna size about 10 x10 m). The higher
the frequency, the smaller the antenna, the smaller the turbulent flow scale that is resolved.
Frequency 50 MHz 405 MHz 915 MHz
Wavelength 600 cm 74 cm 33 cm
Antenna 100 m 13 m 2 m

24. Moments of the Average Doppler

25. Challenges …
Identification of Atmospheric Targets but not the Clear Air echoes
Precipitation echoes
Identification Interference Signal
Identification of Clutter
Identification of Non-Atmospheric Targets
Birds, Planes, non-stationary objects from near by buildings , roads (from Radar Side lobes)

26. NWS NOAA Profiler Network
Typical NPN Profiler Site Equipped With RASS
Profiler Equipment Shelter
404 MHz Coaxial-Colinear Antenna
449 MHz Coaxial-Colinear Antenna

28. Complete Layout of a 404 MHz Co-Co Antenna

30. The vertical velocity of the atmosphere is directly measured by the vertical beam.
Wind Profilers detect minute fluctuations in atmospheric density, caused by the
turbulent mixing of volumes of air with slightly different temperature and moisture
content.

31. The signal power is a measure of the amount of backscattered power received from
the atmosphere. High signal power values (greater than 60 dBZ) are typically
associated with high moisture content or the presence of precipitation particles, while
low power values (less than 40 dBZ) usually indicate a dry or stable atmosphere.
Meteorological features such as moisture advection and cloud layers, vertical extent
of convection, and bright bands (inferring the 0 degree C level) are all visible at
times in the signal power displays.

32. RASS (Radio Acoustic Sounding System)
A profiler site equipped with the RASS
option has the capability to measure and
produce vertical temperature profiles.
The speed of sound is affected by the
temperature of the atmosphere. Sound
travels through the atmosphere at
slightly different speeds at different
temperatures. RASS uses this principal
to track the speed of the acoustic
energy emitted from the RASS
Transducers as the sound waves
propagate up through the atmosphere.
The temperatures of the atmosphere at
specific heights are extrapolated from
the speed of the RASS wave propagation.

33. Vertical RASS Temperature Profile (One Week)

34. NPN site locations