SIST EN IEC 61400-50-2:2022

SLOVENSKI STANDARD
01-december-2022
Sistemi za proizvodnjo energije na veter - 50-2. del: Meritve vetra - Uporaba talne
tehnologije za daljinsko zaznavanje (IEC 61400-50-2:2022)
Wind energy generation systems - Part 50-2: Wind measurement - Application of ground-
mounted remote sensing technology (IEC 61400-50-2:2022)
Windenergieanlagen - Teil 50-2: Windmessungen - Anwendung der bodengestützten
Fernerkundungstechnologie (IEC 61400-50-2:2022)
Systèmes de génération d'énergie éolienne - Partie 50-2: Mesurage du vent - Application
de la technologie de télédétection montée au sol (IEC 61400-50-2:2022)
Ta slovenski standard je istoveten z: EN IEC 61400-50-2:2022
ICS:
27.180 Vetrne elektrarne Wind turbine energy systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 61400-50-2

NORME EUROPÉENNE
EUROPÄISCHE NORM October 2022
ICS 27.180
English Version
Wind energy generation systems - Part 50-2: Wind
measurement - Application of ground-mounted remote sensing
technology
(IEC 61400-50-2:2022)
Systèmes de génération d'énergie éolienne - Partie 50-2: Windenergieanlagen - Teil 50-2: Windmessungen -
Mesurage du vent - Application de la technologie de Anwendung der bodengestützten
télédétection montée au sol Fernerkundungstechnologie
(IEC 61400-50-2:2022) (IEC 61400-50-2:2022)
This European Standard was approved by CENELEC on 2022-10-04. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
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Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61400-50-2:2022 E

European foreword
The text of document 88/829/CDV, future edition 1 of IEC 61400-50-2, prepared by IEC/TC 88 "Wind
energy generation systems" was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN IEC 61400-50-2:2022.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2023-07-04
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2025-10-04
document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 61400-50-2:2022 was approved by CENELEC as a
European Standard without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated:
IEC 61400-12-1:2017 NOTE Harmonized as EN 61400-12-1:2017 (not modified)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod), the
relevant EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 61400-50-1 - Wind energy generation systems - Part 50- EN IEC 61400-50-1 -
1: Wind Measurement - Application of
Meteorological Mast, Nacelle and Spinner
Mounted Instruments
Under preparation. Stage at the time of publication: FprEN IEC 61400-50-1:2022.
IEC 61400-50-2 ®
Edition 1.0 2022-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –

Part 50-2: Wind measurement – Application of ground-mounted remote sensing

technology
Systèmes de génération d'énergie éolienne –

Partie 50-2: Mesurage du vent – Application de la technologie de télédétection

montée au sol
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.180 ISBN 978-2-8322-5602-2

– 2 – IEC 61400-50-2:2022 © IEC 2022
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Symbols, units and abbreviated terms . 10
5 General . 11
6 Classification of RSDs . 13
6.1 General . 13
6.2 Data acquisition . 14
6.3 Data preparation . 15
6.4 Principle and requirements of a sensitivity test . 15
6.5 Assessment of environmental variable significance . 21
6.6 Assessment of interdependency between environmental variables . 22
6.7 Calculation of accuracy class . 24
6.8 Acceptance criteria . 26
6.9 Classification of RSD . 27
7 Verification of the performance of RSDs . 27
8 Evaluation of uncertainty of measurements by RSDs . 30
8.1 General . 30
8.2 Reference uncertainty . 30
8.3 Uncertainty resulting from the RSD calibration test . 30
8.4 Uncertainty due to RSD classification . 32
8.5 Uncertainty due to non-homogenous flow within the measurement volume . 33
8.6 Uncertainty due to mounting effects . 34
8.7 Combining uncertainties in the wind speed measurement from RSD (u ) . 34
VR,i
9 Additional checks . 34
9.1 Monitoring the performance of the RSD at the application site . 34
9.2 Identification of malfunctioning of the RSD . 34
9.3 Consistency check of the assessment of the RSD systematic uncertainties . 34
9.4 In-situ test of the RSD . 35
10 Application to SMC . 36
11 Reporting. 36
11.1 Common reporting on classification test, calibration test, and monitoring of
the RSD during SMC . 36
11.2 Additional reporting on classification test . 37
11.3 Additional reporting on calibration test . 37
11.4 Additional reporting on SMC . 38
Annex A (informative) Uncertainty due to non-homogenous flow within the
measurement volume . 39
Bibliography . 40

Figure 1 – Tilt angular response V ∕V of a cup anemometer as a function of flow
α  α=0
angle α compared to cosine response (IEC 61400-50-1) . 17

IEC 61400-50-2:2022 © IEC 2022 – 3 –
Figure 2 – Deviation versus upflow angle determined for an RSD with respect to the
cup anemometer in Figure 1 . 17
Figure 3 – Example of sensitivity analysis against wind shear . 19
Figure 4 – Example of wind shear versus turbulence intensity . 23
Figure 5 – Example of percentage deviation of RSD and reference sensor

measurements versus turbulence intensity . 23
Figure 6 – Comparison of 10 min averages of the horizontal wind speed component as
measured by an RSD and a cup anemometer . 29
Figure 7 – Bin-wise comparison of measurement of the horizontal wind speed
component of an RSD and a cup anemometer . 29

Table 1 – Interfaces from other standards to IEC 61400-50-2 . 12
Table 2 – Interfaces from IEC 61400-50-2 to other standards . 12
Table 3 – Bin width example for a list of environmental variables . 18
Table 4 – Parameters derived from a sensitivity analysis of an RSD . 20
Table 5 – Ranges of environmental parameters for sensitivity analysis . 21
Table 6 – Example selection of environmental variables found to have a significant

influence . 22
Table 7 – Sensitivity analysis parameters remaining after analysis of interdependency
of variables . 24
Table 8 – Example scheme for calculating maximum influence of environmental
variables . 25
Table 9 – Preliminary accuracy classes of an RSD considering both all and only the

most significant influential variables . 26
Table 10 – Example final accuracy classes of an RSD . 26
Table 11 – Example of uncertainty calculations arising from calibration of an RSD in
terms of systematic uncertainties . 31

– 4 – IEC 61400-50-2:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
WIND ENERGY GENERATION SYSTEMS –

Part 50-2: Wind measurement – Application of
ground-mounted remote sensing technology

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
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Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC 61400-50-2 has been prepared by IEC technical committee 88: Wind energy generation
systems. It is an International Standard.
This first edition of IEC 61400-50-2 is part of a structural revision that cancels and replaces the
performance standards IEC 61400-12-1:2017 and IEC 61400-12-2:2013. The structural revision
contains no technical changes with respect to IEC 61400-12-1:2017 and IEC 61400-12-2:2013,
but the parts that relate to wind measurements, measurement of site calibration and assessment
of obstacle and terrain have been extracted into separate standards.
The purpose of the re-structure was to allow the future management and revision of the power
performance standards to be carried out more efficiently in terms of time and cost and to provide
a more logical division of the wind measurement requirements into a series of separate
standards which could be referred to by other use case standards in the IEC 61400 series and
subsequently maintained and developed by appropriate experts.

IEC 61400-50-2:2022 © IEC 2022 – 5 –
The text of this International Standard is based on the following documents:
Draft Report on voting
88/829/CDV 88/865/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 61400 series, published under the general title Wind energy
generation systems, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.

– 6 – IEC 61400-50-2:2022 © IEC 2022
INTRODUCTION
This part of IEC 61400 specifies procedures and methods which ensure that wind
measurements using ground-mounted remote sensing devices are carried out and reported
consistently and in accordance with best practice. This document does not define the purpose
or use case of the wind measurements. However, as this document forms part of the IEC 61400
series of standards, it is anticipated that the wind measurements will be used in relation to some
form of wind energy testing or resource assessment.
The main clauses of this document are not mutually dependent. Therefore, it is possible that a
user will refer to only certain of the main clauses rather than all clauses to adapt this document
to their specific use case. However, the main clauses are presented in a logical sequence that
could be applied in practice.
The technical content of this document could previously be found in IEC 61400-12-1:2017 [1] .
Because of the increasing complexity of this source document, IEC TC 88 decided that a re-
structuring of the IEC 61400-12 series of standards into a number of more specific parts would
allow more efficient management and maintenance going forward. This document has been
created as part of that re-structuring process.
___________
Numbers in square brackets refer to the Bibliography.

IEC 61400-50-2:2022 © IEC 2022 – 7 –
WIND ENERGY GENERATION SYSTEMS –

Part 50-2: Wind measurement – Application of
ground-mounted remote sensing technology

1 Scope
IEC 61400-50 specifies methods and requirements for the application of instruments to
measure wind speed (and related parameters, e.g. wind direction and turbulence intensity).
Such measurements are required as an input to some of the evaluation and testing procedures
for wind energy and wind turbine technology (e.g. resource evaluation and turbine testing)
described by other standards in the IEC 61400 series. This document is applicable specifically
to the use of ground-mounted remote sensing wind measurement instruments, i.e. devices
which measure the wind at some location generally above and distant from the location at which
the instrument is mounted (e.g. sodars, vertical profiling lidars). This document specifically
excludes other types of RSD such as forward facing or scanning lidars. This document specifies
the following:
a) the procedure and requirements for classifying ground-based RSDs in order to assess the
uncertainty pertaining from sensitivity of the RSD response to meteorological conditions that
can vary between the RSD calibration place and time and the use case (specific
measurement campaign – SMC) place and time;
b) the procedures and requirements for calibration of RSDs;
c) the assessment of wind speed measurement uncertainty;
d) additional checks of the RSD performance and measurement uncertainty during the SMC;
e) application of the wind speed uncertainty derived from the RSD calibration and classification
to the measurements taken during the SMC (e.g. interpolation of uncertainty or calibration
results to different heights);
f) requirements for reporting.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 61400-50-1, Wind energy generation systems – Part 50-1: Wind measurement –
Application of meteorological mast, nacelle and spinner mounted instruments
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp

– 8 – IEC 61400-50-2:2022 © IEC 2022
3.1
accuracy
closeness of the agreement between the result of a measurement and a true value of the
measurand
3.2
complex terrain
terrain surrounding the test site that features significant variations in topography and terrain
obstacles (3.10) that can cause flow distortion
3.3
data set
collection of data sampled over a continuous period
3.4
flow distortion
change in air flow caused by obstacles, topographical variations, or other wind turbines that
results in the wind speed at the measurement location being different from the wind speed at
the wind turbine location
3.5
hub height
height of the centre of the swept area of the wind turbine rotor above the
ground at the tower
Note 1 to entry: For a vertical axis wind turbine the hub height is defined as the height of the centroid of the swept
area of the rotor above the ground at the tower.
3.6
measurement period
period during which a statistically significant database has been collected for the use case
EXAMPLE power performance test
3.7
measurement uncertainty
parameter, associated with the result of a measurement, which characterizes the dispersion of
the values that could reasonably be attributed to the measurand
3.8
measurement volume
region within which wind flow characteristics can influence a wind speed
measurement and which is defined by the scan geometry, device configuration or arrangement
of the multiple beams penetrating the volume in order to acquire that measurement
3.9
method of bins
data reduction procedure that groups test data for a certain parameter into intervals (bins)
Note 1 to entry: For each bin, the number of data sets or samples and their sum are recorded, and the average
parameter value within each bin is calculated.
3.10
obstacle
obstruction that blocks the wind and creates distortion of the flow
Note 1 to entry: Buildings and trees are examples of obstacles.

IEC 61400-50-2:2022 © IEC 2022 – 9 –
3.11
pitch and roll angles
levelling angles
3.12
power performance
measure of the capability of a wind turbine to produce electric power and energy
3.13
probe volume
region from which a single constituent physical measurement of, for example, Doppler
shift or radial velocity, is acquired, several of which are typically required to derive a wind speed
measurement
Note 1 to entry: The probe volume is a characteristic of the basic physical interaction of the remote sensing device
with the atmosphere, rather than the wind speed measurement derived from these interactions, which is determined
by the flow within the measurement volume.
3.14
radial velocity
line of sight velocity
projection of the wind speed vector onto the RSD line of sight
3.15
standard uncertainty
uncertainty of the result of a measurement expressed as a standard deviation
3.16
swept area
projected area of the moving rotor upon a plane normal to the
axis of rotation
Note 1 to entry: For teetering rotors, it is assumed that the rotor remains normal to the low-speed shaft. For a
vertical axis wind turbine, it is the projected area of the moving rotor upon a vertical plane.
3.17
test site
location and surroundings where an RSD is deployed for the purpose of providing
measurements as part of a test of, for example, a wind turbine or testing of the RSD
3.18
wind shear
change of wind speed with height
3.19
wind shear exponent
α
exponent of the power law defining the variation of wind speed with height
Note 1 to entry: This parameter is used as a measure of the magnitude of wind shear and can be otherwise useful.
The power law equation is:
α
z

i
(1)
vv=
zi h
H
where
v is the hub height wind speed;
h
H is the hub height (m);
v is the wind speed at height z ;
zi i
α is the wind shear exponent.
– 10 – IEC 61400-50-2:2022 © IEC 2022
3.20
wind veer
change of wind direction with height
4 Symbols, units and abbreviated terms
Symbol Description Unit
avg 10 min average
c slope in linear regression m/s
d
data in bin i
i
number of environmental variables considered to have a relevant influence on the
M
accuracy of the remote sensing device according to the classification test
m slope in linear regression
slope describing the sensitivity of the wind speed measurement of the remote
m
sensing device on the environmental variable j as gained from the combination of
j
the results from a minimum of 3 classification tests
m
maximum slope
max
m
minimum slope a month
min
m
slope of the nth test
n
N total number of data points in dataset

N
number of classification tests
CT
n
number of bins according to the ranges of variables given in Table 3
b
n
number of data points in bin i
i
REWS rotor equivalent wind speed
RSD remote sensing device
r coefficient of determination in linear regression

SMC specific measurement campaign
std standard deviation
added category B standard uncertainty at measurement height j (not covered by
u
added_systematic,j,i
the meteorological mast)
u
added category B uncertainty at the height of the top of the meteorological mast
added_systematic,1,i
u
cumulated other category B uncertainties of the remote sensing device at height j
systematic,j,i
cumulated other category B uncertainties of the remote sensing device at the
u
systematic,1,i
height of the top of the meteorological mast
u
standard uncertainty of calibration test in bin i in accordance with 8.3 m/s
ver,i
u uncertainty components combined to calculate the category B uncertainty for wind
VR,i
speed measurements from an RSD
u
uncertainty related to the classification of the RSD

VR,class,i
u uncertainty related to the flow variation across the measurement volume of the
VR,flow,i
RSD
u
uncertainty due to the in-situ test
VR,isc,i
u
uncertainty related to the mounting of the RSD
VR,mnt,i
u
uncertainty related to the monitoring of the RSD
VR,mon,i
u
uncertainty due to the verification test
VR,ver,i
u uncertainty due to operational characteristics of the RSD at control mast height in
VRcls,mh,i
bin i
u
uncertainty of the RSD verification at control mast height in bin i
VRvrf,mh,i
IEC 61400-50-2:2022 © IEC 2022 – 11 –
Symbol Description Unit
V
mean value of the reference wind speed in bin i m/s
ref,i
V
cup wind speed
cup
v
wind speed based on remote sensing device measurements m/s
RSD
v
wind speed based on reference sensor measurement m/s
reference
v
wind speed measured by the reference wind speed sensor m/s
reference
v
wind speed of the RSD at control mast height in bin i
RSD,mh,i
v
wind speed of the control mast in bin i
MM,i
V
bin average of RSD at calibration test in bin i m/s
RSD,i
V
bin average of reference measurement at calibration test in bin i m/s
Ref,i
x centre of range covered by x and by the verification test x
centre SMC verification_test
expected upper range limit of not measured environmental variable j in wind
x
max,j,i
speed bin i
expected lower range limit of not measured environmental variable j in wind
x
min,j,i
speed bin i
maximum range of the environmental variable x between the SMC and the
x
range
verification test (i.e. maximum of ranges of x and x )

SMC verification_test
environmental variable considered in the RSD classification and measured during
x
SMC
the SMC
environmental variable considered in the RSD classification and measured during
x
verification_test
the SMC
x mean value of the environmental variable j in wind speed bin i as present during
SMC,j,i
the specific measurement campaign
mean value of the environmental variable j in wind speed bin i as present during
x
ver,ji,
the calibration test of the remote sensing device
α
upflow angle into the probe volume
α upflow angle out of the probe volume
Φ opening angle of the RSD from the vertical
standard deviation of the percentage wind speed deviations of the 10 min data in
σ(d )
i
bin i
5 General
This document defines methods and requirements for carrying out wind measurements using
ground-mounted remote sensing devices (sodars and lidars). Requirements for calibration,
classification and mounting are described. Wind measurements carried out in accordance with
this document are useable for many purposes in the field of wind energy (e.g. power
performance measurement, site assessment, load measurement, noise measurement). The
specific standard relating to the intended use case of the wind speed measurements should be
referred to for limitations and additional requirements (e.g. height of measurement relative to
turbine hub height in the case of power performance measurements). For wind measurements
carried out using cup or sonic anemometers mounted on a meteorological mast or turbine
nacelle, refer to IEC 61400-50-1. Interfaces between this document and other standards are
summarized in Table 1 and Table 2.

– 12 – IEC 61400-50-2:2022 © IEC 2022
Table 1 – Interfaces from other standards to IEC 61400-50-2
Interface description Reference to other Reference to Short use Format
standard IEC 61400-50-2 description
Mounting of sensors IEC 61400-50-1 Subclause 6.1 Mounting of reference
on meteorological sensors on
masts meteorological masts
for RSD calibration
and classification
Assessment of IEC 61400-12-5 Subclause 6.2 Filtering the dataset From [deg]
obstacles and terrain to [deg]
Side-mounted IEC 61400-50-1:2022, Assessing the
Subclause 6.2
instruments on Subclause 10.4 influence of
meteorological masts meteorological mast
wake on the RSD
measurement
Assessment of IEC 61400-50-1:2022, Subclause 6.2
sectors free of Subclause 9.3
meteorological mast
wake
Uncertainty of side- IEC 61400-50-1:2022, Subclause 6.2 Estimating additional
mounted instruments Clause 11 uncertainty due to
on meteorological correction of
masts meteorological mast
effect on reference
sensor in RSD
calibration and
classification
Classification of mast- IEC 61400-50-1:2022, Subclause 6.3
mounted wind Clause 6
sensors
Mounting of sensors IEC 61400-50-1 Clause 7 Mounting of reference
on meteorological sensors on
masts meteorological masts
for RSD calibration
and classification
Post-calibration or in- IEC 61400-50-1:2022, Clause 7 Application of RSD
situ calibration of Subclause 11.3.3 post-calibration or in-
Subclause 9.4
wind sensors situ calibration
Calibration of mast- IEC 61400-50-1:2022, Subclause 8.1 Estimating uncertainty
mounted sensors Clause 11 of reference sensors
in RSD calibration
Table 2 – Interfaces from IEC 61400-50-2 to other standards
Interface Reference to Reference to other Short use
Format
description IEC 61400-50-2 standard description
Definition of RSD Subclause 6.1 IEC 61400-12-1 Definition of RSD Heights in metres
measurement measurement [m]
Subclause 9.1
heights for a power heights for
curve measurement classification, hub
Clause 10
height, REWS
and/or shear
measurement for a
power curve
measurement
When compared to measurements from a meteorological mast-mounted cup anemometer,
remote sensing device (RSD) measurements typically display some degree of scatter. Some of
this scatter arises due to the sensitivity of the RSD to various environmental conditions (e.g.
temperature and wind shear). It is the task of the classification test (Clause 6) to identify and
quantify these sensitivities for a number of discrete heights covering the measuring range of
interest. As for cup anemometers it is assumed that these sensitivities will be type specific and

IEC 61400-50-2:2022 © IEC 2022 – 13 –
the classification test needs to be performed for each type of RSD for a minimum of two
instruments of each type and at a minimum of two locations.
The remaining scatter in the cup anemometer comparison is considered to be random noise.
This arises from a variety of sources. For example, the turbulent de-correlation in the wind due
to the distance between the measurement locations leads to scatter. Also, the distance between
the individual probe volumes of the remote sensor itself could contribute to such scatter. The
random noise is assumed to be unit and site specific, i.e. it can vary between different
evaluations of the same RSD.
Depending on the specific use case (e.g. resource assessment, power performance test, etc),
a particular unit of an RSD could require a verification test (Clause 7) before being deployed
for the specific measurement campaign (SMC). In some situations, it may alternatively be
possible to perform the verification test during the SMC (e.g. during the power performance
test). This test is a comparison of the RSD measurements to those from calibrated cup
anemometers mounted on a meteorological mast spanning a significant portion of the height
range of interest. The purpose of this test is to convey traceability to international standards to
this particular device, in the form of an uncertainty. Usually the SMC using the RSD will take
place at a different location and at a different time and therefore with a different distribution of
environmental conditions than for the RSD verification test. Depending on the sensitivities
identified during the classification test, the different environmental conditions will alter the
performance of the RSD, increasing the uncertainty in relation to that determined in the
verification test. Expressions for the uncertainty of the RSD are given in Clause 8.
Clause 9 describes how the cup anemometer measurements from a short meteorological mast
can be used to monitor the performance of the RSD. By ensuring at least one common
measuring height, it is possible to assess whether the uncertainty obtained in the classification
and the verification test is consistent with the performance of the RSD during the SMC. If
inconsistencies are identified from this monitoring, the corresponding uncertainties used in the
SMC are increased. This provides a useful "safety net" for the methodology and a feedback
mechanism that should promote realistic uncertainty assessments.
Reporting requirements for the complete methodology are given in Clause 11.
6 Classification of RSDs
6.1 General
The accuracy of the RSD can be influenced by meteorological variables. As the meteorological
conditions during the SMC can be different from those prevailing during the RSD performance
verification test, such influences are linked to additional uncertainty. It is therefore necessary
to investigate the sensitivity of the performance of the RSD to meteorological variables. The
results of such tests shall identify the variables that influence the performance of the RSD and
determine the classification of the instrument.
The simplest of these evaluations entails considering the difference between the RSD
measurement and a reference measurement as a function of one meteorological variable at a
time. An accuracy class of the RSD shall be evaluated for certain ranges of various
environmental variables similar to the classification of cup anemometers in accordance with
IEC 61400-50-1, based on the empirical analysis of the sensitivities observed during
classification tests. Care should be taken to allow for the possible interdependency of
environmental variables (e.g. wind shear and turbulence intensity) so that sensitivities are not
inadvertently double counted. The uncertainties arising due to RSD classification can then be
evaluated.
A case-specific accuracy class may also be evaluated based on the sensitivities of the remote
sensing system and the variation of the environmental variables observed during the RSD
performance verification and SMC. It should be clearly stated whether a classification result
has been derived generically on multiple units or whether it is based on a case-specific
evaluation.
– 14 – IEC 61400-50-2:2022 © IEC 2022
6.2 Data acquisition
The classification test is based on concurrent measurements obtained by the RSD and a tall
reference meteorological mast with which it is compared. The measurements shall be co-
located, such that they characterize flow within the same volume of air. The degrees of
concurrency and co-location that shall apply to the measurements are those that enable the
determination of the most precise and well understood relationship between them. In particular,
the following apply.
a) The same averaging intervals shall be used for the RSD and reference sensor being
compared: 10 min averages shall be recorded. In addition to 10 min averages, the standard
deviations and extreme values of the measured variables within the 10 min periods shall be
recorded.
b) The number of samples acquired by each instrument during each averaging interval to
obtain an average shall be recorded.
c) It shall be noted whether the individual samples acquired within the averaging interval by
the RSD are cumulative values, representing, for example, a spectrum integrated from the
beginning of the averaging interval to the moment at which the sample is acquired. This will
have a bearing on statistics that require successive samples to be independent, such as
standard deviation used in, for example, turbulence assessments.
d) The device shall be sited and analysis of the measurements conducted in a manner that
minimizes extraneous influences on the relationship between the RSD and reference sensor
measurements. These influences can include, but are not limited to, flow perturbations, fixed
echoes, and real variations in the flow between the RSD measurement volume and the
reference instrument measurement location. The distance between the meteorological mast
and the RSD shall be a compromise allowing good correlation between meteorological mast
and RSD measurements, while at the same time preventing or limiting the influence of the
meteorological mast on the RSD.
e) The meteorological mast-mounted reference sensors shall comply with the requirements of
IEC 61400-50-1. This applies especially to the calibration, classification and mounting.
f) The reference meteorological mast should have a constant cross section and solidity across
its height. In this way, the influence of the meteorological mast on boom-mounted
anemometers remains constant with height and allows a more accurate comparison of the
measured wind shear between the meteorological mast and the RSD.
The RSD and reference sensors shall be synchronized to within 1 % of the averaging interval,
and this degree of synchronization shall be verified and tested for drift at least once a week. If
comparison of time stamps indicates drift has occurred, the RSD system clock shall be reset to
synchronize with the reference sensor system clock and remote sensing data time stamps
adjusted to compensate for the drift over the period during which it is evident by linear
interpolation.
Data shall be acquired until the following data coverage requirements are fulfilled.
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