Anemometers Assignment

D.I.T. Kevin St. Anemometry
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Department of Electrical Services Engineering
Aneomometry
Course Code / Year DT 018
Module Electrical services engineering and energy
management.
Lecturer Mr. Derek Kearney.
Student Name Wayne Doyle, Mark Stewart, Eamon Carroll
Paul Derwin
Student Number D06112499,D05110728,D06111916,
D07114349.
SubmissionDate 29th
November2011

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Word Count 9494
Declaration
I hereby certify that the material, which is submitted in this assignment/project,
is entirely my own work and has not been submitted for any academic
assessment other than as part fulfilment of the assessment procedures for the
program Bachelor of Science in Electrical Services and Energy Management
(BSc (Hons)) (DT 018).
Signature of student:…………….………
Date:…………………………

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Table of Contents:
Page No.
Declaration ......................................................................................................................2
Table of Contents:..........................................................................................................4
Table of Figures:.............................................................................................................6
1.0 Introduction..........................................................................................................7
1.1 Wind. ....................................................................................................................7
2.0 Anemometry........................................................................................................9
3.0 Rotational anemometers .................................................................................10
3.1 Cup anemometer .............................................................................................10
3.2 Propeller anemometer.....................................................................................13
4.0 Phase shift anemometers ...............................................................................14
4.1 LIDAR (Light Detection and Ranging) ..........................................................14
4.2 Sonic anemometers.........................................................................................17
5.0 Pressure Type Anemometers.........................................................................19
5.1 Pressure plate...................................................................................................19
5.2 Pressure Tube Anemometer (Pitot tubes) ...................................................20
6.0 International standards....................................................................................22
6.1 Cup & Propeller Anemometer Test Procedures..........................................22
6.1.1 IEC 61400-12-1.....................................................................................22
6.1.2 ASTM D5096-02...................................................................................24
6.2 Phase shift anemometers...............................................................................25
6.2.1 Sonic Anemometer Test Standards...................................................26
6.2.2 ASTM D 6011-96..................................................................................26

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6.2.3 ISO 16622..............................................................................................28
6.2.4 IEC standard 61400 .............................................................................30
6.3 Environmental conditions and inspections...................................................31
6.4 Standards Conclusion .....................................................................................31
7.0 Comparison of the performance ....................................................................32
7.1 Over speeding: .................................................................................................32
7.1.1 Dynamic filtering in Turbulent Winds .................................................33
7.1.2 Mechanical operation:..........................................................................33
7.2 Phase shift anemometers–Ultra Sonic anemometers, SODAR and
LIDAR anemometers. .............................................................................................34
7.2.1 2.1Ultra sonic anemometers...............................................................34
7.2.2 SODAR and LIDAR..............................................................................35
7.3 Thermoelectric anemometers ........................................................................36
7.3.1 Hot wire anemometers.........................................................................36
8.0 The development and effect of turbulence in relation to wind
measurement ....................................................................................................38
8.1 The Importance of Accurate Wind Measurement .......................................38
8.1.1 What is Turbulence ..............................................................................38
8.2 Turbulence Effect on Wind Measurement Devices ....................................40
8.2.1 Cup Anemometer..................................................................................40
8.2.2 Propeller Type.......................................................................................41
8.2.3 Sonic Anemometer...............................................................................42
8.2.4 SODAR...................................................................................................43
8.2.5 LIDAR Anemometer .............................................................................43
8.2.6 Cup vs LIDAR........................................................................................44
9.0 References ........................................................................................................46

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Table of Figures:
Page No.
Fig 1 (Anon., 2011) ........................................................................................................7
Fig 2 (Gripe, 2004) .......................................................................................................10
Fig 3 (Dines, 1911 ) .....................................................................................................11
Fig 4 (Anon., 2010) ......................................................................................................13
Fig 5 (wright, 2006) ......................................................................................................14
Fig 6 (technology, 2011) .............................................................................................16
Fig 7 (Johnson, 2001)..................................................................................................18
Fig 8 IEC performance requirements........................................................................23
Fig 9 (Brazier, 1914) ....................................................................................................23
Fig 10 ASTM D 5096-02 Calibration Test Speed Protocol, ascending and
descending speeds (Coquilla, 2009).........................................................................25
Fig 11 wind tunnel requirements for ASTM D 6011-96 sonic sensor testing
(Adam Havner, 2008) ..................................................................................................27
Fig 12 Otech Eng. Wind Tunnel Laboratories (ASTM Inernational, 1996) .........29
Fig 13(Webb, 2007) ....................................................................................................38
Fig 14(Horst, 2007) .....................................................................................................39
Fig 15(Horst, 2007) .....................................................................................................39

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1.0 Introduction
Measurement of wind speed is very important to people such as pilots, sailors,
and farmers and engineers. Accurate information about wind speed is important
in determining the best sites for wind turbines. Wind speeds must also be
measured by those concerned about dispersion of airborne pollutants. Wind
speeds are measured in a wide variety of ways, ranging from simple go-no go
tests to the most sophisticated electronic systems. The variability of the wind
makes accurate measurements difficult, so rather expensive equipment is often
required.
1.1 Wind.
What is wind? Wind is created by
different in pressure. When pressure
differential exists the air is accelerated
from a higher to a lower pressure. So
when the sun strikes the earth it heats
the soil near the surface. In turn the soil
warms up the surrounding air .With
warm air being less dense than cool
air,just like a helium balloon it rises. Cool air then rushes in to take
its place and is then heated its self and continues the cycle. The
cycle is continues just like a crank shaft in a car and as long as the solar engine
is driving . (Gripe, 2004) Due to it rotating sphere the error will be deflected by
the Cariolis Effect except exactly on the equator. Globally, there are two major
driving factors of large-scale winds the atmospheric circulation, and the
differential heat between the equator and a pulse and the rotation of the plants.
The wind rises from the moves north and south in the higher layers of the
atmosphere. At around 30° in both hemispheres the cariolis force prevents the
air from moving much further. At this latitude there is a high pressure area, as
the air begins sinking down again. As the wind rises from the equator there will
be a low-pressure area close to ground level attracting wins from the north and
Fig 1(Anon., 2011)

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south. Then at the north and South Pole there will be a high pressure due to the
cooling of the air at the poles.

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2.0 Anemometry
An anemometer is device fundamental used for measuring wind speed and is a
common weather station instrument .The term its self is derived for the Greek
word anemo which means wind. The first known descriptions seam to show that
an inventor by the name of Leon Battista gives a description of an anemometer
in the year 1450. (W.E. Knowles Middleton, 1968) Anemometers can be broken
down mainly into two categories those that measure wind velocity an those that
measure wind pressure these are close linked (W.E. Knowles Middleton, 1968)
As stated above Anemometers can be segregated into four categories
according to their operational and physical characteristics.
1. Rotational anemometers – cup anemometers, and propeller
anemometers.
2. Phase shift anemometers – ultra sonic anemometers, and laser
Doppler anemometers.
3. Pressure type anemometers – pressure tube anemometers, pressure
plate anemometers, and sphere anemometers.
4. Thermoelectric anemometers – hot wire anemometers, and hot plate
anemometers. (Kearney, 2011)
This document will also review international standards from the International
Organization for Standardization (IOS), International Electro technical
Commission (IEC) and American Society for Testing Materials (ASTM).
whom govern anemometry calibration and wind measurement. The purpose
of these standards is to provide the methodology that will ensure accuracy
and reproducibility in the measurement and analysis of anemometers. They
are intended to aid manufacturers, installers and purchasers of
anemometers.

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3.0 Rotational anemometers
3.1 Cup anemometer
Cup anemometers are one off the most common types of anemometer used
today worldwide. It is a very simple design and operation. The cup anemometer
was invited the Irish astronomer Thomas T. R. Robinson of Armagh
Observatory in 1846. Miditon (1969) identified that the first anemometers had
four hemispherical cups each mounted on a horizontal arms which are then
mounted on equal angles to each other. The
unit was then mounted on a vertical access.”
The wind would then flow past any the cups
in any of the horizontal access inducing a
radial motion which was proportional to the
wind velocity therefore allowing for counting
the cup turns over a set time which allow him
to then produce an average wind velocity
over a rage of wind velocities (Spilhaus,
1953) (Dines, 1911 ).Around the end of the
1920s much research and experimenting was
carried out in relation the number of cups and
also the length of the arms. When the
incident was designed the anemometer
wrongly claimed that no matter how big the
cups or how long the arms were cups would
always move warned that the speed of the wind. This is apparently confirmed
by some early independent experiments but it turned out to be very further from
the truth Brazier and Paterson found that a three arm cup rotor is optimal with
respect to sensitivity and suppression of the unevenness in the rotation
(“wobbling”).A modern cup is shown below in figure 3. (Brazier, 1914) Paterson
and Braziar also demonstrated the literate is better on a shorter diameter.
(Brazier, 1914) (Kristensen, 2005) Patrson also determined that optimum
Fig 2(Gripe, 2004)

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number of cups is three and can be proven
in his equation 𝑓 =
𝑢
𝑟𝑠
where r=radious of
the cup and U= angular velocity and S=
the cup rotor.
The wind would then flow past any one of
the cups in of the horizontal access
inducing a radial motion which was
proportional to the wind velocity therefore
allowing for counting the cup turns over a
set time which allow him to then produce
an average wind velocity over a rage of
wind velocities (Spilhaus, 1953).A modern
cup is shown in figure 3. The cup anemometers are probably the most common
type anemometer currently being used today; it can also be fitted with a vain to
determine the mean of the horizontal wind
velocity components. It has proven over time that such combinations sturdy,
reliable and robust Instrumentation package. They are simple to operate and
can be used in a wide range of applications in weather stations at airports wind-
farms, solar farms and can also be used on large structures such as high-rise
buildings and bridges which are under construction or the equipment being
used to construct them i.e. tower cranes.
The behaviour of a couple anemometers in turbulent wind can cause systematic
errors in the measurement of the wind speed. One of the main errors which
have been identified is a so-called over speeding. This is gives an increased
wind speed measurement or velocity than the actual wind speeds. This is due
to the anemometer responding quickly to an increased wind speed and
responding much slower to decrease in winds in the wind speed, this allows the
cup and anemometer to continue rotating at a faster velocity than the actual
wind speed it is measuring. “Based on an equation of the dynamic response of
cup anemometer and the contrast observations between cup anemometer and
sonic anemometer, it is shown that the error caused by the over speed of cup
anemometer is between 1% and 3 % and data processing error (DP error)
Fig 3(Dines, 1911 )

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associated with cup anemometer is the most important one because of distinct
calculated methods (vector mean and scalar mean). After the reduction for DP
error, the rational wind speed values could be obtained”. (Kristensen, 2005)
The following equation is used to demonstrate over speeding as a percentage
E = I². (1.8d – 1.4)
Where:
E is the percentage of over speeding error
I is the turbulence intensity
d is the distance constant for the anemometer(Energy, 2008)
In one form or another cup anemometers are often used with a wind vane for
determining the mean of the horizontal wind velocity component. Such
combinations are sturdy and reliable instrument packages. They are easy to
operate and are used at weather stations, airports, wind farms, and sites where
large structures, such as bridges, are under construction. Cup anemometers
are relatively in expensive to manufacture and are suitable for many wind
measurement applications. The three types of cup anemometer has now
become the standard for this type of anemometer. The cup anemometer is a
mechanical device or instrument with a long proven reliable track record which
is easy to find certification for the use in contractual applications. Researchers,
Educational Institutes, Meteorologists and many of the general public are
familiar with cup anemometers. Although they are one of the oldest ways of
measuring wind speed you will find that most people will have no problem
accepting easily understood mechanical designs. Cup anemometer designs
vary considerably according to the particular application. Several Cup
Anemometer Manufacturers offer different models which include low cost
portable wind speed measurement, homeowner anemometers , industrial wind
speed checking and high specification models for scientific research and
weather analysing High specification cup anemometers will normally be
designed to withstand changing conditions and more solid construction
materials and overall design will not only increase the lifetime of the device but

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also render it more valuable in terms of accuracy and repeatability in conditions
that are subject to change. (Tong, 2010)
3.2 Propelleranemometer
Propeller anemometer and sometimes also now as
wind mill anemometers or aero vanes usual
consist of four bladed propeller. The blades are
constructed of extremely light weight Martials such
as carbon fiber, aluminum or thermo setting
plastics. The device functions predominantly in on
the lift force. With airflow parallel to its axis the
propeller blades experience a lift force which turns
the propeller at a velocity or speed proportional to
the winds speed or velocity. In this case the wind
turns a propeller instead of cups. Small propeller anemometers are used to
check the velocity and direction of the turbulence. A propeller anemometer is
used where the direction of the wind changes, as it does out-of-doors. The
propeller blades indicate the correct wind velocity only when they face the flow
of the wind. The vane, which also shows the direction of the wind, keeps the
propeller properly aligned. Propeller types generally
have a driven shaft with an ac or dc generator integrated to the device. The
types of propeller used for wind applications have a fast response time and
produce a linear output for the changing speeds. These devices can be as
simple as a magnet on the rotating shaft passing a coil inducing a voltage which
can be represented as a wind speed depending how many times the magnet
passes the coil over a set time.
Figure 1
Fig 4(Anon., 2010)

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4.0 Phase shift anemometers
4.1 LIDAR (Light Detection and Ranging)
LIDAR (Light Detection and Ranging) was first demonstrated in the United
States of America in the late 1960 early 1970.The widespread use and
development of the technology has been hampered over the years due to the
complexity and the high cost associated with LIDAR systems. “However the
recent year’s developments of new LIDAR systems based on fibre optic
components which have been proven in the telecommunication’s industry seem
to show a large cost reduction and
improvement in the overall design and
also an improved compactness”.(wright,
2006)
LIDAR is a remote sensing technology
analogous radar .The range (distance)
to an object is determined by measuring
the time delay between transmission
and reflection of a signal. LIDAR is used
for remote sensing which will give
“temporal and spatial resolution”
(wright, 2006).Doppler LIDAR works by the emitting light energy and
backscattered from the microscopic particulates or aerosols being transmitted
by the wind such as dust pollen and water molecules. This difference in the
frequency being emitted and the frequency being received back is called the
Doppler shift which in turn is proportional to the velocity of the particles.
The need for atmospheric LIDAR to meet eye safety standards limits both the
intensity of the light energy and its highest frequency (shortest wavelength) that
can be focused and radiated. When these criteria are combined, LIDARs used
for atmospheric measurements use midrange infrared light generated by lasers
operating with wavelengths in the 1.5 to 2 μm range like High resolution
Fig 5(wright, 2006)

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Doppler LIDAR (HRDL).Modern equipment is highly sensitive, they are fitted
with electronic amplifiers which have allowed LIDAR technics like HRDL to
measure wind fields to a distance of several kilometres even when the air is
clean and it contains a very low number of particles that result in backscatter
(wright, 2006). Generally LIDAR is used to measure atmospheric wind in two
general forms continues wave (CW) or pulsed. CW LIDAR continuously emits
its light energy through its optics which focus the beam in a predetermined
radios ahead of the instrument. Within the focus of radios, the backscatter
energy is collected and the velocity of the wind is measured from using the
Doppler shift. (N.D. Kelley, 2007) CW wind-finding LIDARs typically perform a
conical scan sequence in which one or more 360º scans are performed at a
fixed elevation angle and focus position. (N.D. Kelley, 2007) CW LIDARS only
produce measurements of the mean horizontal wind vector at a few heights. But
as is highlighted in by the national renewable energy laboratory it has proven to
be very accurate when some optimal smoothing is applied.
Pulse LIDAR emits regular spaced emissions of highly regulated light energy
which is spaced apart at regular emissions of highly collimated light energy for a
specific and predetermined time (pulse length) similar to Doppler SODAR. The
return signals then isolated to a period of time which corresponds to a specific
segment of radial distance along a beam called “the range gate” (N.D. Kelley,
2007) The backscattered signals which are digital extracted from the gate are
then processed to “derive the line of sight (LOS) or radial velocities along the
path of the LIDAR(N.D. Kelley, 2007) Pulsed LIDAR typically operates with a
pulse repetition or sampling frequency ranging from 200 to 1000 pulses per
second. The resulting vertical wind profile derived from a pulsed LIDAR using a
conical scan incorporates a much greater vertical resolution than an equivalent
CW profile. (N.D. Kelley, 2007)Sound propagation in the atmosphere has been
studied for at least 200 years, but it has only been in the last 50 years
that acoustic scattering has been used as a means to study the structure of the
lower atmosphere. In the United States during World War II,
acoustic backscatter in the atmosphere was used to examine low-level
temperature inversions as they affected propagation in microwave
communication links. Beginning in the late 1960's and early 1970's, scientists at

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the U.S. National Oceanic and Atmospheric Administration demonstrated the
practical feasibility of using acoustic sounders to measure winds in the
atmosphere by means of the Doppler shift.(technology, 2011)
During the 1980s there was a similar development of Doppler SODAR systems
by other U.S companies. The Xondar SODAR system which was capable of
making wind profile and turbulence measurement. Another company was
developing their pulsed Doppler SODAR system, this system was an Invisible
Tower system.(technology, 2011)Like its cousin technologies, radar (radio
detection and ranging) and LIDAR (light detection and ranging), SODAR uses
waves for measurement; and, as the name suggests, it uses sound waves.
Over the past few decades SODAR has been typically used to research
atmospheric conditions which would include insect migration patterns and
pollution.
Commercial SODAR in today's wind industry are ground-based systems that
send up focused sonic beams in rapid succession, producing an audible chirp.
Wind turbulence sends a portion of the sound back towards the ground as an
echo. By precisely measuring the frequency and time delay of the echo (aka the
Doppler shift), the SODAR device using trigonometry measures the wind speed
and direction at any height up to around 200 meters. This is why the SODAR
are also called Doppler SODAR.(secondwind, 2011)Commercial SODAR
systems and other remote sensing systems were developed and
commercialized for the wind industry to help reduce to overall inaccuracy in
measuring wind velocity below the turbines hub height.
SODAR are now used as a resource assessment by
wind farm operators either in conjunction with a
microwave towers or as a standalone SODAR is
important to wind meteorologists because it is ideally
suited to measuring the lower bound below the sweep
of radar and above the ground. This is where wind
matters most to wind turbines as shown below in figure
6.SODAR have gained commercial acceptance in wind development
applications because they measure the wind at higher
Fig 6(technology, 2011)

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heights than is practical using meteorological towers.Sonic Detection and
ranging SODAR systems are classified as remote sensing as they do not have
to place a sensor at the location where the measurement is required They are
used to remotely measure the vertical turbulence structure turbulence structure
and the profile of the lower layer of the atmosphere. SODAR systems operate in
a similar manner to radar (radio detection and ranging) systems except that
sound waves rather than radio waves are used for detecting. (secondwind,
2011)
Because of their ability to be easily transported, SODAR systems are also well
suited to more specialized wind development application such as wind
prospecting (also known as scouting or site finding). Wind shear measurement,
because of their ability to measure wind at many different heights, SODAR is
particularly valuable to when looking for information in relation the amount and
the type wind shear and veer. Because of the extreme difference in the velocity
of the wind and the constant changing of direction has been identified as a
substantial factor in the increase in wear and tear of wind turbines. The
information gained to understand the wind shear on a particular site helps to
identify the suitably of the site for a wind turbine.(secondwind, 2011)
4.2 Sonic anemometers
Some articles show that sonic anemometers were developed first in the 1970s
others state that it was developed by a Dr Andreas Pflitsch in 1994. And in a
report written by the department of metrology Indian the sonic anemometer was
first developed in the 1950s with some
confusion over its origins but there is no
confusion over the usefulness of this
instalment its self. But whichever year it
was developed there is no doubt in the
benefits of the device.
Wind velocity is measured based on the
time it takes for sonic pulses to travel
between a pair of transducers.Using the

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combined measurements from several transducer pairs mount on the end of
arms mounted perpendicular to each other, we can then yield a measurement
of air flow in 1, 2 or 3 dimensions. The technic used are also based on the
principles of Doppler shift. The transducers emit acoustic signals which travel
up and down through the air and because the speed of the sound moving
through still air is different from that through still air.
A typical path length between the transducers is 10 - 20cms and this gives us
the special resolution. A temporal resolution of 20 Hz or better
can be achieved which makes this technology well suited for the purposes of
turbulence measurements.(Mathew, 2009)
One of the great advantages of ultrasonic anemometers is their lack of moving
parts which makes them appropriate for usage in Automatic Weather Stations
and in harsh environments. The lack of moving parts makes them appropriate
for use in automated weather stations in the wind turbine industry and
renewable energy industry. Some limitations of sonic anemometers are when
they are exposed snowy conditions the anemometer does not work.
Fig 7(Johnson, 2001)

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5.0 Pressure Type Anemometers
5.1 Pressureplate
The pressure plate or normal plate anemometer consists of a swinging plate
which is held at the end of a horizontal arm. The arm is attached to a shaft
which it is free to rotate around. A wind vane ensures that the pressure plate is
always facing perpendicular to the wind flow. The wind blows against the plate
and the distance that the arm travels is directly calibrated to the force of the
wind. It operates on the principle that the force of moving air on a plate held
normal to the wind is
Fw = cAρ u2/2
Where
Ais the area of the plate
ρis the density of air
uis the wind speed
cis a constant depending on the size and shape of the plate but not greatly
different from unity.
This force produced is then used to drive a recording device directly or as input
to a mechanical to electrical transducer. Research of gust studies is the main
application of this type of anemometer because of its very short response time.
Gusts with a duration of as little as 10ms can be examined with this type of
anemometer. A pressure plate anemometer is however not very sensitive to low
winds and is likely only to give an estimate of wind speed and is also not very
responsive to the turbulence dynamic of wind. A pressure plate anemometer is
useful for spraying agricultural chemical or for estimating wind chills. (Johnson,
2001)

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5.2 PressureTube Anemometer(Pitot tubes)
Pitot tubes are commonly used to measure air flow in ventilation systems
because they can be easily installed into ventilation systems through small ports
in the duct work. Accuracy can be as high as +/- 2% if great care is taken when
taking Pitot tube readings. The pressure tube anemometer measure the height
of a liquid in a u tube which has one bent into a horizontal direction to face the
wind and the other end would usually be open and facing up so the wind can
pass over, this will create a vacuum due to the Bernoulli effect. The height of
the liquid is usually measured with a float connected to a mechanical linkage to
a recording device. A disadvantage of the pressure tube anemometer is that the
moving parts can wear out. The liquid manometer can also be fragile. To get an
accurate reading the Pitot tube must be faced into the wind stream. External
weather conditions can have an effect on the performance of the pressure tube
anemometer.

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6.0 International standards
6.1 Cup & PropellerAnemometer TestProcedures
6.1.1 IEC 61400-12-1
The International Electro-technical Commission (IEC) is a global standards
organization that consists of committees that review operational practices in
electrical and electronic industry and research. The IEC also publishes
international standards in collaboration with the International Organization for
Standardization (ISO) (Coquilla, 2009).
Cup and Propeller Anemometer test procedures are carried out to determine
the transfer of the instruments voltage output to wind speed. According to the
IEC, these procedures should be conducted in a uniform, horizontal and steady
state flow of low turbulence levels these conditions are best achieved in a
purpose built wind tunnel.
 The anemometer shall be mounted on a stand similar to that used in the
field in the wind tunnel.
 Prior to every calibration the set up shall be verified by means of a
comparative calibration of a reference anemometer.
 The anemometer shall be run for five minutes prior to calibration to avoid
the effect of large temperature variations on the mechanical friction of the
anemometer bearings.
 Calibration shall be carried out in wind speeds ranging between 4 and
16m/s at 1m/s interval, the sequence of speeds are as follows, 4, 6, 8,
10, 12, 14, 16, 15, 13, 11, 9, 7, and 5m/s. This rising and falling speed
sequence is to identify any hysteresis during the test.
 For data collection at the desired speed, the sampling frequency shall be
at least 1 Hz at a sampling interval of 30 seconds (Coquilla, 2009).

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below lists the IEC performance requirements for a wind tunnel calibration
facility.
Wind
characteristic
tunnel
Description Minimum requirement
Blockage ratio Anemometer ratio plus mount
frontal area to the total wind
tunnel test section area
Not to exceed 0.1 for open test
sections, 0.05 for closed
sections
Flow uniformity Percent difference in wind speed
within the test section volume
Less than 0.2% in the
longitudinal, transversal, and
vertical directions
Horizontal wind
gradient
Dynamic pressure differential at
the area covered by the rotating
cup anemometer
Must be less than 0.2%
Turbulence
intensity
Ratio between the wind speed
standard deviation to the main
speed
Must be less than 2%
Fig 8IEC performance requirements
.
It is noted by the IEC that it is important that the anemometer calibration test is
carried out with a steady uniform horizontal flow across the cup or propeller
anemometer, with no vertical or cross flow conditions. The wind tunnel section
should be turbulence free. According to the IEC, cup anemometers are to be
calibrated to a pilot-static tube
system, which is also calibrated to
an appropriate test speed (Coquilla,
2009).The IEC standard states the
reference wind speed from a Pitot-
static tube system is calculated
using the differential pressure
Fig 9(Brazier, 1914)

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measured at the inlet of the Pitot-static tube and also the measurements of the
local conditions inside the wind tunnel test section. The IEC requires equipment
used to measure pilot tubes to be traceable back to a standards authority.
6.1.2 ASTM D5096-02
ASTM D 5096-02 is a Standard Test Method for Determining the Performance
of a Cup and Propeller Anemometer Test Procedures, which were published in
1990(Smith, 2009). The ASTM (American Society for Testing Materials) is a
non-profit voluntary standards organization, which develops and publishes
standards. The purpose of ASTM D5096-02 is to provide a method for
calibration and performance characteristics for the cup and propeller
anemometers. Some of the characteristics include starting threshold and off-
axis response. Wind tunnel requirements for ASTM 5096-02 cup and propeller
anemometer testing include some of the following criteria.
 Anemometer front area must be less than 5% of the test section cross-
section area of the wind tunnel testing equipment.
 Turbulence must be less than 1% in the test area.
 Wind speed-reading must maintain an accuracy of 0.1m/s.
 Air density profile in test area must be less than 3% difference.
 Flow uniformity in the test area must be constant to within 1% (Coquilla,
2009)
6.1.2.1Steps from ASTM calibration procedure
1. Install the anemometer at an angle of attack maintained within 0.50
2. Acquire wind tunnel speed and anemometer rotation rate along with test
section environmental conditions. Each test will run between 30 and100
seconds. At each test speed collect data.
3. Calibration is carried out at two times the threshold (U0) of the
anemometer and up to 0.5 times the max application speed (Umax).
Incremental test speeds are defined in table 2 that shows ascending and
descending speeds on the next page. They are 20 different test speeds.

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4. Calculate and report wind speed residuals by determining a wind speed
value for a range of anemometer rotation rates using linear transfer
functions and then subtracting the predicted value from the measured
wind speed.
5. Construction of new data beyond the range of measurement is not
required therefore if the max test speed is 50% of Umax, then the transfer
function only applies for that test speed.
Ascending speeds Descending speeds
2 times U0
3 times U0
4 times U0
5 times U0
6 times U0
0.1times Umax
0.2 times Umax
0.3 times Umax
0.4 times Umax
0.5 times Umax
0.5 times Umax
0.4 times Umax
0.3 times Umax
0.2 times Umax
0.1 times Umax
6 times U0
5 times U0
4 times U0
3 times U0
2 times U0
Fig 10ASTM D 5096-02 Calibration Test Speed Protocol, ascending and descending
speeds (Coquilla, 2009)
6.2 Phase shift anemometers
Standards that are available for the performance testing of sonic anemometers
are ASTM D 6011-96 and ISO 16622, which involves a test program that
evaluates the three-dimensional characteristics of sonic anemometers. For
sonic sensors used in research applications, where it may be necessary to map
complex flows at high resolution, such detailed test procedures for the sonic
instrument may be necessary. However, some of the most common industry

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applications for sonic anemometers generally only require a certain level of
uncertainty in two dimensional wind speed and direction measurements such as
on weather stations, airports, oceanic buoys, nuclear power plants, wind plants,
and many others. Thus, a more practical test protocol, extracted from published
test standards, may be applicable for verifying sonic anemometer measurement
6.2.1 Sonic Anemometer Test Standards
Two standards that define procedures for sonic anemometer testing are ASTM
D 6011-96 and ISO 16622. These standards describe the initial calibration for a
sonic anemometer in a zero-wind chamber, which involves the measurement of
the path length and transient times between the transmitter and receiver. ASTM
D 6011-96 is a sonic anemometer test standard, which was released in 1996
and is intended to assist wind instrument manufacturers in the development and
design of sonic anemometers. Test facilities also use it as a guide for evaluating
the performance of sonic anemometers used in specific applications.
6.2.2 ASTM D 6011-96
ASTM D 6011-96 procedures include measurements of the following
 Acoustic path length
 System delay
 System delay mismatch
 Thermal stability range
 Velocity resolution
 Shadow correction,
 Velocity calibration range
 The acceptance angle
The first five tests are done in a zero-wind chamber, which defines the initial
calibration transfer characteristics of the instrument. The following three tests,
shadow correction, velocity calibration range, and acceptance angle, define the

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necessary correction to the initial calibration transfer characteristics these are
determined in a wind tunnel
Wind tunnel
characteristic
Minimum requirement
Blockage Anemometer front area is less than 5% of the test section
C.S.A.
Wind speed
capability
Must be able to reach speeds up to 50% of the application
range and must maintain speed within +/- 0.2m/s. wind tunnel
speeds from 1.0 to 10m/s be maintained at +/- 0.1m/s.
Flow uniformity Flow profile in the test section must be constant to within 1%
Turbulence Must be less than 1% in the test section
Air density
uniformity
Density profile in test section must be less than 3% difference
Wind speed reading Maintain a relative accuracy of 0.1m/s to its traceable source
Fig 11wind tunnel requirements for ASTM D 6011-96 sonic sensor testing (Adam Havner,
2008)

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6.2.3 ISO 16622
ISO 16622, an international standard for used for anemometer performance
testing was released in September 2002 and is similar to ASTM D 6011-96, the
following steps define ISO 16622,
 “Zero wind chamber tests: the offset of the measured wind speed is
determined over the operational temperature range.
 Wind tunnel test: the deviation of the measured from the true velocity
(vector) is determined over the operational range of flow speed and
direction.
 Pressure chamber test: the operational range of air density is
determined. Although the measuring principle does not depend on air
density, a minimum density is required to transmit detectable sound.
 Field test: addresses the response to potentially adverse environmental
conditions, which are difficult to simulate in the laboratory” (ISO 16622
International Standard, 2002).
The ISO 16622 requirements for wind tunnels are similar to ASTM D 6011-96
but the wind tunnels shall be capable of producing wind speeds that cover the
full range of the anemometer to be calibrated. The wind speed must be kept
within +/- 0.2m/s. For angle testing the rotating fixture must have a 1° angular
resolution. The wind tunnel test procedures are as follows
 Senor positioned at zero angle of attack, low wind speed is selected. To
test for orientation +/- 360 degrees around its vertical axis at 5-degree
increments and step has an increase in wind speed (e.g. 18%, 32%,
56% and 100% of the max test speed).
 With the sensor positioned vertically at zero angle of attack and rotated
at the worst-case orientation. Tests are carried out at different
percentages of the test speed.
 The steps above are repeated with the sensor tilted 15 degrees into the
wind and 15 degrees away from the wind (Coquilla, 2009).

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Fig 12 Otech Eng. Wind Tunnel Laboratories (ASTM Inernational, 1996)

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6.2.4 IEC standard 61400
Technical requirements for LIDAR and SODAR anemometers have being
revised under the IEC standard 61400-12-1. The purpose of these standards is
to ensure traceability, repeatability of SODAR/LIDAR measurements and
uncertainties of measurements. The main requests of these standards are an
accuracy test and sensitivity test/classification (Albers, 2010).
Accuracy Test & Calibration
Unlike mechanical anemometers such as cup and propeller types, LIDAR and
SODAR anemometers cannot be tested in wind tunnels due to the large size of
the wind scanning volume. The only way to calibrate the instruments is to
compare each individual LIDAR and SODAR to calibrated reference sensors in
open field tests. According to IEC 61400-12-1the comparisons of the LIDAR
and SODAR anemometers against a reference sensor must capture the wind
speed range between 4 and 16m/s similar to wind tunnel test speeds.
If the difference of the measured wind speed exceeds the reference sensor
measurement, the relation of the LIDAR/SODAR wind speed measurement and
the reference sensor measurement should be applied for a calibration of
LIDAR/SODAR. This calibration is then linked to the following; statistical
uncertainly of the comparison and uncertainty of the reference sensor.
The test and calibration cannot be more accurate than the cup anemometer
reference sensor (Albers, 2010).
6.2.4.1Sensitivity Test/ Classification
Environmental conditions such as wind shear, turbulence intensity effects the
operation and accuracy of the LIDAR/SODAR anemometers, therefore
uncertainty of the LIDAR/SODAR wind measurements due to sensitivity to
environmental conditions needs to be assessed.
According to IEC 61400-12-1, the outline for the sensitivity test/classification is
the same as the accuracy test/calibration. The sensitivity of the LIDAR/SODAR
anemometers is based on set environmental variables. The percentage change

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of the LIDAR/SODAR and cup anemometer per 10-minute period is considered
as one environmental variable at a time.
6.3 Environmentalconditions and inspections
A wind vane/ sonic anemometer should be capable of use under the following
conditions.
a) Operating temperature range:
 Equipment installed outdoors − 25 °C to + 55 °C
 Equipment installed indoors − 15 °C to + 55 °C.
b) Operating time: continuous.
c) Operating power range: The operating level can be set from 100V to 240V
for AC voltage, or from 12V to 24V for DC voltage. The tolerance level for
the set figures shall satisfy the requirements of IEC 60945.
6.4 Standards Conclusion
In this report, the four published standards that define procedures for calibrating
anemometers are IEC 61400-12-1, ASTM D5096-02, ASTM D6011-96 and ISO
16622. According to Coquilla the only publication related to the wind industry is
IEC 61400-12-1. Most test facilities are able to perform test procedures from the
standards listed above. The test procedures explains and defines necessary
steps manufacturers need to carry out to calibrate anemometers, this ensures
that all anemometers are traceable back to international standards organization.
LIDAR/SODAR and sonic anemometers use the same standards, ISO 16622
and IEC 61400-12-1 for calibrating.

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7.0 Comparison of the performance
The cup anemometer is the preferred wind speed measurement instrument for
site assessments or proposed wind farm performance evaluations. This
anemometer is an inexpensive and rugged sensor appropriate for turbulence
measurements for wind-energy measurement applications. Both propeller and
cup anemometers are the most suitable for a wide variety of environments
including marine applications. The propeller anemometer differs in that they
require an orienting vane to keep the propeller facing into the wind thus
provides both wind speed and direction information in a single unit. The design
of the rotational anemometer is such that the rate of rotation is linearly
proportional to the wind speed. This means the anemometer responds primarily
to that portion of the wind vector that is parallel to the rotor axis.
Aspects of rotational anemometry which may cause concern when specifying
are:
 Over Speeding
 In-ability to sense vertical wind components
 Mechanical operation
 Dynamic filtering in turbulent winds. (Energy, 2008)
7.1 Over speeding:
Over speeding occurs during fluctuating wind speeds. Instruments have time
constant characteristics, i.e. the response to change of an input parameter.
Generally the time to react to change is not linearly proportional to the
magnitude of that change in parameter however this is not the case with cup
anemometers, with fluctuating wind speed the mean indication of a cup
anemometer will be higher than the actual average wind speed, the results
showing that a cup anemometer will respond more quickly to positive changes
in wind speed and not as quick to negative changes.

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7.1.1 Dynamic filtering in Turbulent Winds
As stated above cup anemometers cannot follow the wind speed fluctuations
exactly, wind fluctuations of higher magnitude reduce the ability of the
anemometer to provide an accurate reading and indication of the changes in
magnitude of the wind vector. However by reducing the arms that support the
cups shall improve the performance and ability to operate in turbulent
conditions. Sensitivity to the wind vector depends upon the ratio of torque to
rotational inertia. As a consequence to dynamic filtering in turbulent winds the
spectral power indicated by a cup anemometer will be lower than what is the
actual power of the wind resulting in an incorrect evaluation of the true
turbulence intensity. The inability to react to the turbulent dynamic is a main
disadvantage of a rotational anemometer. This will result in directional
overshoots that can place the rotor of the main wind axis resulting in a lower
wind speed reading that the actual wind speed. This is more common in low
wind speeds with variance flow conditions and the wind direction is consistently
changing rapidly. False wind speed measurements can also occur due to off
axis flows in a vertical direction. This is particularly true for propeller – vane
anemometers installed on sloping terrain or near abrupt topographical features
which can have a constant vertical wind component or frequent large vertical
velocities. The dynamic response of a helicoid propeller to wind speed changes
decreases when the angle between the flow and axis increases, for example
when the angle with respect to the rotor axis reaches 85 degrees, its distant
constant has tripled.
7.1.2 Mechanical operation:
In the absence of mechanical friction the performance and steady state
calibration results should be perfectly linear but friction is always present to
some extent. Rotational Anemometers like their counterparts can fail totally,
however more seriously can partially fail. Due to their mechanical construction
they are more susceptible to breakdown i.e. bearing seizure. Preventative

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maintenance is necessary for the anemometer and/ or introducing forms of
redundancy to the measurement system. Such preventative maintenance and
calibration should be performed on a regular basis to maintain the low-wind
speed performance and to detect increased drag from bearing wear. (Energy,
2008)
Environmental concerns must be taken into consideration. Low temperatures
can cause particular problems for cup anemometers. The accumulation of
ice/snow in the cups will cause a change in aerodynamic behaviour, and
appropriate measures need to be taken to detect when such conditions occur.
Lightning strikes must be considered to ensure that a strike does not damage
the test equipment, a lightning finial/spike should be mounted at the top of the
mast, complete with a down conductor installed to carry the strike to Earth and
surge arrestors installed should they not be incorporated in the data logging
equipment. Another particular disadvantage of the rotational anemometer is
relative to the necessity of the erection of a mast. It may prove difficult to attain
planning permission if the mast was to impose on the environmental landscape.
7.2 Phase shift anemometers–UltraSonic anemometers,
SODAR and LIDAR anemometers.
7.2.1 2.1Ultra sonic anemometers
Ultra sonic anemometers main operational attribute is that they are non-
mechanical, this in turn omits many of the problems associated with cup and
propeller anemometers explained previously as the lack of moving parts
reduces continued calibration and maintenance needs, although they are similar
in that, both rotational and Ultrasonic anemometers are both linearly
proportional to the wind speed.
Accurate measurement of the three-dimensional wind vector can be obtained
using the 3-axis sonic anemometer, and provide both wind speed and direction
from a single unit as with the bi-vane propeller, where cup anemometers

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cannot. Sonic anemometers do it in a time resolution much higher than both a
cup anemometer and propeller anemometer. Although hot wire anemometers
can have sampling rates in the order of 10 kHz, their fragility in harsh
environmental conditions and the necessity to keep the wire free of dust
deposits can pose a great problem in their operation. Due to their complex
construction the cost of these anemometers can be significant. Other notable
problems associated with sonic anemometers include false readings at the
sensor can be obtained should the complex structure cause flow distortions by
impeding the wind vector. Acoustic blockages of the transducers can also be
caused by rain drops, ice, snow and other debris on the transducers, and
therefore not suited for marine applications as with the cup anemometer.
7.2.2 SODAR and LIDAR
SODAR is classed as a remote sensing system as it does not use a sensor to
directly measure the wind speed (Manwell, et al., 2003)
SODAR and LIDAR both are remote sensing device systems that are ground
level based and capable of measuring wind speeds at a range of heights .A
clear advantage is not requiring a large mast to mount the measurement
devices on thus having less visual impact on the surrounding environment.
SODAR is also primarily only able to give information on mean wind speed and
does not provide information on wind gusts. (Anon., 2011) .
SODAR and Ultra sonic anemometers both operate using acoustic principles
however differ greatly in their operating measurement range. As discussed
earlier Sonic anemometers study wind structure by emitting frequency between
closely spaced transmitters and receivers, whereas SODAR instruments look at
larger scale structures using a combined transmitter/receiver and being a
remote sensing tool, SODAR does not disturb the flow in the way that a met
mast does.
Defining wind profiles and evaluating higher elevation wind speeds using
SODAR, proves to be much more cost effective than their counterparts using
mast mounted meteorological instruments therefore SODAR is of clear
relevance to MW scale turbines. SODAR and LIDAR are ideal for short term

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data collection as they are portable, however considerations should be taken
should they be required for longer terms as the instruments could be subject to
vandalism or theft. Although portable, SODAR requires a steady surface ruling
them out of off-shore. SODAR can also measure the three dimension wind
vector should more than one antenna orientated in a different direction be
utilised. Vertical wind profiling can be derived using the Doppler effect of both
SODAR and LIDAR anemometry by measuring the propagation time.
The typical uncertainty in measurement of wind speed using SODAR is about 2
to 4%. Recent developments in SODAR have indicated improvement in
accuracy in correlation with wind speed and direction of up to 80 m/s with a 2%
difference for mean wind speed between SODAR and cup anemometry. (Lang
& McKeogh, 2011)SODAR systems are not yet in widespread use for wind
energy applications. They are not cost effective for smaller turbines and the
choice of suppliers is limited.
7.3 Thermoelectric anemometers
7.3.1 Hot wire anemometers
A hot-wire anemometer as stated earlier consists of a tungsten-wire element
heated by an electrical current. The hot wire anemometers works on the
principle of temperature coefficient of resistance. There are two types of
circuitry utilised in the construction of the heated sensing element constant-
temperature or constant-power. The constant-temperature sensor maintains a
constant temperature differential between a heated sensor and a reference
sensor; the amount of power required to maintain the differential is measured as
an indication of the mass flow rate of the wind vector. Constant-temperature
anemometers are popular because of their high-frequency response, low
electrical noise level, immunity from sensor burnout when airflow suddenly
drops, compatibility with hot-film sensors, and their applicability to liquid or gas
flows but have also serious limitations. The hot wire anemometers are
susceptible to atmospheric contamination, are expensive, require large power
inputs and do not respond to low wind speeds resulting in false readings.

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Atmospheric contamination such moisture will cause the thermometer to be
inaccurate and will ultimately lead to corrosion. They are less popular because
their zero-flow reading is not stable, temperature and velocity response is slow,
and temperature compensation is limited. The importance to correct flow
temperature changes during calibration, as well as changes which occur
between calibration and measuringsituations to standard conditions is a cause
for concern. The main cause of error in thermal anemometry is not accounting
for flow temperature changes. To reduce this affect calibration by measuring
both velocity and temperature effects of the thermal anemometer or by taking
measurements should be carried out in the same temperature controlled
apparatus that the calibration of the anemometer was completed. (Finaishand,
1994).

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8.0 The development and effect of turbulence in
relation to wind measurement
In this section will discussed the development and effect of turbulence in
relation to wind measurement and discuss the how anemometers perform in
these conditions.
8.1 The Importanceof Accurate Wind Measurement
When assessing a site for a potential location for the introduction of wind energy
it is important to understand the necessity of collecting accurate information. In
turbulent environments it can be difficult to collect accurate data due to
problems such as volatile wind conditions. This type of problem can cause
errors in initial calculations of data collection for a proposed wind farm which
could lead to a project becoming a finical disaster.
8.1.1 What is Turbulence
Turbulence can be caused by surface ‘roughness’, this describes the nature of
the land in which the wind flows over (Katerina Syngellakis, 2007). It is a major
problem as it can cause wind turbine operation to perform irregularly and
ultimately cause the wind turbine to break down due to wear and tear caused by
the turbulent winds. Below table 1 gives an indication where hot spots for
turbulence may arise.
Fig 13(Webb, 2007)
In relation to wind energy/measurement the problem of turbulence can be found
in built up areas such as urban cities. In this section it is hope to explain the role
of the built environment in the creation of turbulence. For example Figure 1 and
2 show a graphic of wind flowing against a building; the arrows represent the

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current state of the wind flow at the point of interaction with the building. This is
hoped to highlight the danger of placing wind energy technology such as wind
turbines in turbulent environments without taking all the necessary
elements/data into account. The graphics in figure 1 and 2 show how this
turbulence occurs when wind flows around buildings and other obstacles found
in urban environments. These obstructions in the path of the wind flow cause
the wind flow to become distorted, this creates turbulence. These flow
disturbances can be seen in Figures 1 and 2. In Figure 1, a view of the side of
building can be seen; this shows how the wind flows over the top of the building.
The size of the arrows in the graphics demonstrates the intensity of the wind.
The shorter arrows and the arrow in the blue colour show how weak the wind
flow is while the longer arrows represent the wind at a high velocity. The section
with yellow arrows shows the area where there is the strongest wind, the
direction of this wind is mostly constant. It can be concluded from the two
graphics that if the turbine is best placed in the middle of the roof, this area is
the location with the least amount of turbulence and where the wind is also at its
strongest(Horst, 2007).
Fig 14(Horst, 2007)Fig 15(Horst, 2007)

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8.2 Turbulence Effecton Wind MeasurementDevices
Traditional large scale wind turbines are designed to be located in open areas
such as rural areas or off shore where the wind characteristics can be
measured accurately. Measuring and collecting wind data for wind turbines
located in turbulent areas such as an urban environment can be a problem. In
non-turbulent areas conventional methods of collecting wind data experiences
very little fluctuations in wind speed or direction. This is not the case when it
comes to turbulent environments, in these environments conventional methods
of collecting data experiences sudden changes in wind speed and direction
frequently. This leads to the technologies which are very successful in their
traditional roles such as a cup anemometer in an open rural area becoming
inaccurate and failing to provide the correct data when applied to a turbulent
area. The following section will focus on individual types of anemometer and
explain the effects of turbulence on these technologies and discuss their
performance in turbulence environment.
8.2.1 Cup Anemometer
A cup anemometer encounters certain difficulties when expose to turbulent
areas. There are two so called difficulties that affect the devices capability to
collect accurate data.
 Over speeding
 Vertical component of turbulent wind
The first problem discussed will be the concept of over speeding and its
possible effects on poor data collection. Over speeding occurs in turbulent
winds where the cup anemometers mean speed result is higher than the true
speed of the wind (B Maribo Pedersen, 2003). This is created by the
fundamental nature of how the cup anemometer works. For this device to work
at all it must respond quicker to an increase in wind speed rather than response
to a decrease in wind speed. These results in a distortion of the true wind speed
as the device spend more time measuring above the mean wind speed then the
time spent below the mean wind speed. This distortion occurs with the presence

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of turbulence and will mean that the reading produced from the cup
anemometer will be larger than the true wind speed (Kristensen, 2005). The
second difficulty with the cup anemometer is the response to the vertical
element of the wind encountered in turbulent areas. It is said that cup
anemometers struggle with the three dimensional nature of the wind flow in a
complex terrain. Cup anemometers are designed to measure the horizontal
wind flow whereas an additional factor is introduced in turbulent environments,
this being the vertical component of the wind (Walker, 2004). These difficulties
have been thought to be the main factors in the problems cup anemometers
have in turbulent areas. Although this may be true, articles featuring
experiments performed have disagreed with these being the main problems and
believe a more fundamental problem is the cause for the larger readings. One
document states that over speeding only accounts for 0.2% of the errors
encountered with over speeding (B Maribo Pedersen, 2003). While another
document puts forward that the design of the cup anemometer is partly the
cause of the higher readings. It details that the shape of the cup can be the
deciding factor on how much an affect the vertical component with have on the
overall reading, stating that a design of a certain type of cup exposed to
turbulent winds can create drag and affect the overall operation of the device.
(A. Albers, 2000).
8.2.2 Propeller Type
The propeller anemometer is a rotational anemometer similar to the cup
anemometer. From research it was found that not many projects trust to
incorporate propeller anemometers solely for wind measurement in turbulent
environments. This is due to them providing limited information on turbulence or
the vertical component of the wind. In turbulent locations propeller type devices
tend to register a lower wind speed; the reason for this is the device has
difficulty maintaining its alignment with the instantaneous wind direction (D.C
Anderson, 2008). Like the cup anemometer the propeller anemometer does not
react accurately to sudden changes in wind speed or direction, this type of
environment being commonplace in turbulent/urban areas. This will have a

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crippling effect and result in essential data not being recorded by the device.
Another interesting point was found in one such article where it stated that a
propeller anemometer cannot measure the vertical component of wind (M.C.H.
Hui, 2009). In turbulent/urban locations the presence of buildings adds a strong
vertical component to the wind (D.C Anderson, 2008). This can in addition to
the reasons shown above explain why a propeller type anemometer may not be
suited to turbulent applications unless incorporated with an additional device.
This statement is backed up by a journal article where it states a propeller
device “dynamic behaviour in turbulent environments may be less than
satisfactory” (Morris et al., Not Stated). Also in this article a cup, sonic and
propeller anemometer are compared in a turbulent environment with the result
being the propeller device been labelled inferior to the two other devices. The
reason stated being the wind speed discrepancy caused by under speeding
(Morris et al., Not Stated). It may also be mentioned that the propeller type
device has problems structurally when exposed to turbulent environments.
8.2.3 Sonic Anemometer
A sonic anemometer is seen as one of the best instrument for the measurement
of turbulence (Bowen, 2008). Advantages of the sonic anemometer include no
moving parts and the fact that it can detect the vertical component of wind
successfully over an extremely quick period of time (D.C Anderson, 2008).
Another advantage is its capability to capture wind and turbulence data in very
low wind. The sonic anemometer compared to cup anemometers in low wind
speed (2ms) shows that cup devices measure higher wind speed more than
sonic 93% of the time. This once again is a problem associated with turbulent
conditions and over speeding (Bowen, 2008). This has caused a lot of
organisations to replace traditional device such as cup anemometers with sonic
anemometers. As discussed above this type of anemometer has an advantage
over cup or propeller devices in that it can measures all three components of
wind (U, V, and W), W being the vertical component which means the sonic
anemometer does not produce non-linearity’s errors which is common with the
more mechanical type devices (B Maribo Pedersen, 2003). One problem with

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this device is how it is affected by the external environment, for example the
presence of rain can affect performance.
8.2.4 SODAR
When a SODAR anemometer is utilized to perform in a turbulent area the result
usually ends up with the device underestimating data. This is due to the devices
inability to detect small scale fluctuations. A SODAR anemometer has a low
sampling rate and when used in turbulent areas it is exposed to large sampling
rates. This causes the underestimation in the devices produced wind data (R
THOMAS, 1991). Another disadvantage of SODAR is that when placed in urban
areas they tend to pick up noise disturbance causes by passing cars etc. This
distortion can lead to the device underperforming in these conditions.
8.2.5 LIDAR Anemometer
LIDAR anemometers are challenging cup anemometers in some areas of wind
measurement as hub heights increase. Remote sensors are becoming popular
in this area. This type of situation would be located at wind farms where there is
a flat terrain. The performance of LIDAR in more complex terrain where there is
unpredictable wind flow is in question. LIDAR performance in flat terrain is good
where it only shows a small percentage of error (Ferhat Bingol, 2009). Its has
been found though when LIDAR is assigned to collecting wind data in more
turbulent areas the error level can go as high as ten per cent. This error occurs
as result of the workings of the LIDAR anemometer, LIDAR use the
“assumption of horizontally homogeneous flow” (Courtney, 2011) to calculate
horizontal wind speed. This works well in non-turbulent flat areas. The error of
up to ten per cent occurs in the unpredictable wind flow which is caused by
turbulence; this turbulence interrupts the element of horizontal wind flow which
the LIDAR usually uses to create good accurate results in settled flat terrain
(Ferhat Bingol, 2009). A possible solution to this problem would be to
incorporate many LIDAR anemometers and aim each one at one point. This will

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result in the assumption of homogeneity of the flow not being required. Also a
downside of the technology is its inability to measure the horizontal component
of wind as accurately as cup or sonic devices (Courtney, 2011)
8.2.6 Cup vs LIDAR
From research it was found that the leading devices in this field are cup and
LIDAR anemometers. It is universally recognised that the cup anemometer is
leading the way but only by a short distance from the emerging LIDAR
technology. It was thought the difference between the two was random noise on
the side of the LIDAR device which caused errors in result. Though one
document argues that evidence from experiments undertaking describe the
difference more to do with the two different probing methods. The cup employs
point measurements while the LIDAR using volume measurements (Courtney,
2008). This problem stands from the fact that when LIDAR measures in volume
it takes into account the vertical and horizontal extents with non-linear
weighting, the difference between the vertical and horizontal measurements
cannot be interpreted (Michael Courtney, 2008). This problem along with the
trouble measuring the horizontal component means the cup anemometer is the
most suited device for use in turbulent environments. It should be noted that all
the devices included in this section are evolving and improving at a rapid rate.

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9.0 References
A. Albers, H. K. D. W., 2000. Outdoor Comparison of Cup Anemometers.
Messung von Wind und Leistung, 1(1), pp. 107-111.
Adam Havner, R. V. C. a. J. O., 2008. Verification Testing of Wind Speed
Measurements from 2D Sonic Anemometers.
Albers, A., 2010. How to gain acceptance for LIDAR measurements. [Online]
Available at:
http://www.windguard.de/filedmin/media/pdfs/UEber_Uns/DEWK_2010/paper_
WindGuard_LIDAR_Acceptance_DEWEK10.pdf
[Accessed 14 november 2011].
Anon.,2010.Camblescientific.[Online]
Availableat:http://www.campbellsci.com.au/05103-l
[Accessed novmber2 7 november 2011].
Anon.,2011.AboutSODAR.Online]
Available:http://www.SODAR.com/about_SODAR.htm
[Accessed 2 October 2011].
Anon.,2011:waterencyclopedia.[Online]
Available_http://www.waterencyclopedia.com/Ce-Cr/Climate-and-the-
Ocean.html
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