i

ii

Introduction
In the Fifth Strategic Energy Plan adopted by the Japanese Cabinet on July 3, 2018, it was decided that the
government will continue to take the measures necessary for the utilization of wind power as a large-scale powersource in the future, such as speeding up environmental assessments and reconsidering scale requirements, andthat it will also work on the promotion of competition and efficiency through the use of the FIT system. For
offshore wind power in particular, it is written that, “Measures will be taken to support the introduction of
offshore wind power generation through the preparation of rules for the use of sea areas and the introduction ofa bidding system. With reference to the measures in Europe, where there has been a rapid reduction of costs inrecent years, we will combine efforts for coexistence with the local regions through the establishment of rules
for the use of sea areas and system constraints, action for base ports and harbors, the acceleration of related
procedures, and price bidding.” In response to this, the Marine Renewable Energy Utilization Act* was enacted
on April 1, 2019. The Sixth Strategic Energy Plan, approved by the Cabinet on October 22, 2021, calls for thepromotion of offshore wind power generation as “a trump card for making renewable energy the main powersource” and a further expansion of its introduction is expected from now on.
When considering a business plan for an offshore wind farm, it is important to obtain accurate wind condition
data in order to evaluate the business feasibility. However, the installation of a meteorological mast at sea
generally requires coordination with the local community, permission and authorization procedures, and highcosts, so measurements using Doppler LiDAR and other remote sensing technologies are being conducted inJapan and overseas. However, with the current remote sensing technology, there have not yet been methods
established to observe the turbulence component of wind speed or the vertical distribution of wind speeds
offshore.
The New Energy and Industrial Technology Development Organization’s “Project to Support Fixed-Bottom
Offshore Wind Farm Development (Establishment of offshore wind resource assessment method)” aims todevelop technologies to establish a rational measurement method for offshore wind conditions in Japan's ocean
areas by utilizing remote sensing technologies such as those mentioned above, and to compile a guidebook of
information that can be used as a practical reference for persons implementing wind measurement.
This “Offshore Wind Measurement Guidebook” (hereinafter referred to as the “Guidebook”) has been
compiled based on the results of this project and with reference to the latest knowledge in Japan and overseas.
It presents the recommended methods (recommended practice) of offshore wind measurement for persons
conducting the wind measurement necessary for offshore wind farm business planning and wind turbine design.
The structure of this Guidebook is as follows.
Chapter 1 describes the positioning and basic concept of this Guidebook and gives an outline of offshore
wind measurement. Chapter 2 describes the measurement of wind conditions and the evaluation of windconditions. From there, Chapter 3 describes measurement using offshore meteorological masts, Chapter 4
describes measurement using dual scanning LiDAR, Chapter 5 describes measurement using single scanning
LiDAR, Chapter 6 describes measurement using vertical LiDAR, and Chapter 7 describes measurement using
a floating LiDAR system. Chapter 8 explains methods for complementing data and evaluating accuracy whenmeasurement data are missing and Chapter 9 describes the items to be included in reports.
*Act on Promoting the Utilization of Sea Areas for the Development of Marine Renewable Energy Power
Generation Facilitiesiii

Members of Technical Committee on Establishment of Offshore Wind Resource Assessment Method
Committee member
Akihiro Honda(Chairperson)
Takeshi Ishihara

Affiliation
Hirosaki University
Professor, Institute of Regional Innovation
The University of Tokyo
Professor, Department of Civil Engineering, Graduate School of Engineering

Hiroyuki Kusaka

University of Tsukuba
Professor, Center for Computational Sciences

Shigehito Nakamura

Japan Wind Power Association
Managing Director

Fumiyo Harada

Development Bank of Japan
Managing Executive Officer(Japanese syllabary order, honorifics omitted)

iv

Revision History
Revision

Revised

RevisedNumberDate

Sections-

2022.06-

Reason for Revision
Published as interim report
Prepared as the deliverable against the project for-2022.09-“Establishment of offshore wind resource assessment
method”

02023.03-0.1

2023.06

4.3.3
Reference

Newly published
Corrected a typo of the equation (4.3)
Unified a notation (no change of contents)v

Table of Contents
1.

Outline ....................................................................................................................................... 1
1.1

Scope ................................................................................................................................. 1

1.2

Contents and relationship of each chapter .......................................................................... 2

1.3

Relevant laws and regulations ............................................................................................ 3

1.3.1 Relevant laws, regulations and ordinances, and their interpretations and explanations .. 3
1.3.2 Japanese standards and guidelines related to laws and regulations ............................... 4
1.3.3 Technical standards ........................................................................................................ 4
1.3.4 Guidelines and recommended standards ........................................................................ 4
1.4
2.

3.

4.

Terms and abbreviations .................................................................................................... 5

Wind measurement and wind condition evaluation .................................................................... 9
2.1

Wind measurement items and evaluation items .................................................................. 9

2.2

Representativeness of wind conditions and selection of measurement points ...................13

2.3

Measurement data evaluation ............................................................................................14

Measurement using offshore meteorological masts ..................................................................15
3.1

Selection of measurement points .......................................................................................15

3.2

Measurement of wind speed and wind direction ................................................................16

3.3

Data analysis .....................................................................................................................18

Offshore measurement using Dual Scanning LiDAR .................................................................19
4.1

Selection of measurement points .......................................................................................194.1.1 Selection of measurement points ...................................................................................19
4.1.2 Installation of equipment ................................................................................................20
4.1.3 Hard target adjustment...................................................................................................20
4.2

Measurement of wind speed and wind direction ................................................................21

4.3

Data analysis .....................................................................................................................224.3.1 Flow of data analysis .....................................................................................................22
4.3.2 Filtering ..........................................................................................................................23
4.3.3 Calculation of horizontal wind speed and wind speed standard deviation ......................23
5.

Offshore measurement using Single Scanning LiDAR ..............................................................25
5.1

Selection of measurement points .......................................................................................25

5.1.1 Selection of measurement points ...................................................................................25
5.1.2 Installation of equipment ................................................................................................25
5.1.3 Hard target adjustment...................................................................................................25
5.2

Measurement of wind speed and wind direction ................................................................26

5.3

Data analysis .....................................................................................................................26

5.3.1 Flow of data analysis .....................................................................................................26
5.3.2 Filtering ..........................................................................................................................27
5.3.3 Calculation of horizontal wind speed ..............................................................................27

6.

Offshore measurement using vertical LiDAR ............................................................................29
6.1

Selection of measurement points .......................................................................................29

6.1.1 Selection of measurement points ...................................................................................29
6.1.2 Installation of equipment ................................................................................................29

7.

6.2

Measurement of wind speed and wind direction ................................................................30

6.3

Data analysis .....................................................................................................................30

Offshore measurement using a Floating LiDAR System ...........................................................32
7.1

Selection of measurement points .......................................................................................32

7.1.1 Selection of measurement points ...................................................................................32
7.1.2 Installation of equipment ................................................................................................33

8.

7.2

Measurement methods ......................................................................................................37

7.3

Data analysis methods ......................................................................................................37

Complementation of missing data and its accuracy verification ................................................38
8.1

System utilization rate and effective data rate ...................................................................38

8.2

Complementation of missing data ......................................................................................38

8.3

Accuracy KPIs and acceptance criteria..............................................................................40

8.3.1 Wind speed and wind direction ......................................................................................40
8.3.2 Wind speed standard deviation ......................................................................................41
8.3.3 Correction of wind speed standard deviation .................................................................429.

Reporting ..................................................................................................................................43
9.1

Installation and measurement reports ................................................................................43

9.2

Evaluation report ...............................................................................................................44

9.3

Verification report ..............................................................................................................44

References .......................................................................................................................................45
Annex A.

Hard target adjustment...................................................................................................47

A.1

Cases when a hard target exists near an offshore measurement point .......................47

A.2

In case of three hard targets ...........................................................................................48

A.3

In case of two or fewer hard targets ...............................................................................50

Annex B.

Pre-deployment verification of accuracy.........................................................................52

B.1

Pre-deployment verification of accuracy ............................................................................52

B.2

Accuracy KPIs and acceptance criteria ..........................................................................52

B.2.1

Wind speed and wind direction ...................................................................................52

B.2.2

Wind speed standard deviation ..................................................................................52

Annex C.

Data acquisition rate check ............................................................................................53

C.3

Data acquisition rate check ................................................................................................53

Annex D.

Example FLS installation work .......................................................................................54

1. Outline
In this Guidebook, the matters to be satisfied are described in the frames at the beginning of each section.
The details outside of the frames supplement and explain the matters to be satisfied.
1.1 Scope
The scope of this Guidebook is the wind measurement necessary for the planning and development ofoffshore wind farms.
In the planning of offshore wind power generation, in order to achieve the purposes below, it is important tounderstand the wind condition characteristics of the installation sea area and to obtain accurate windmeasurement data for the site.
• Consideration of business feasibility• Consideration of wind turbine design conditions• Obtaining permissions and authorizations for construction plans, etc., submitted based on the Electricity
Business Act
The wind measurement data obtained from a site is essential for the reduction of the project risk and theimprovement of the profitability of a project. It is also recommended that wind measurement be conducted forlong period after the operation of an offshore wind farm is started.
The methods for measuring offshore wind conditions are classified into the “direct measurement” using by
cup anemometers and wind vanes, and the “indirect measurement (remote sensing)” performed using
technology such as LiDAR. At present, the use of a fixed-bottom metrological mast can be described as themeasurement method with the highest accuracy, sufficient empirical proof, and possibility of quantifying
uncertainty. However, the installation of a meteorological mast at sea generally requires coordination with thelocal community, permission and authorization procedures, and high costs, so it is desirable that a low costmeasurement method using a remote sensing device (RSD) be established. In addition, the establishment of ameasurement method using a floating wind measurement system is desirable for deep sea areas where floating
offshore wind generation is assumed.
This Guidebook only covers the wind measurement devices which are judged to be technically usable at thepresent time, and other measurement devices are excluded.
This Guidebook has been produced with reference to the latest Japanese and overseas research, guidelines,
and international standards related to offshore wind measurement, and is positioned as a resource that persons
implementing wind measurement can refer to in their work. It has been compiled based on the latest knowledge
with the aim of presenting measurement methods to assist in the optimum wind measurement from theviewpoints of reliability and economic efficiency.

11.2 Contents and relationship of each chapter
The contents and relationship of each chapter of this Guidebook are as shown in Table 1.1.
Table 1.1 Contents of each chapter and relationship with other chapters
Chapter2

Contents
Wind measurement andwind condition evaluation

Explanation
 This chapter summarizes the items to be satisfied

Chapters to bereferenced
Select fromas the evaluation of the wind conditions,

Chapters 3 to 7

regardless of the requirements for the wind

Chapters 8 andmeasurement and the measurement method9adopted.
3

Measurement using
meteorological mast

 This chapter summarizes the requirements when
adopting a measurement mast as the wind

Chapters 2, 8,
and 9

measurement method.
 This is the most reliable measurement.
 High accuracy measurement of turbulence
intensity is possible.
4

Measurement using Dual

 This chapter summarizes the requirements when

Chapters 2, 8

Scanning LiDAR (DSL)

adopting DSL (a method of measurement using

and 9, Annexes

two scanning LiDARs (SL)) for indirect

A, B and C

measurement (remote sensing) as the windmeasurement method.
 It is possible to install the equipment on land andperform offshore measurement, but the observable
range is limited.
 High accuracy measurement of turbulence
intensity is possible by reducing the elevation
angle to below the threshold.
5

Measurement using Single

 This chapter summarizes the requirements when

Chapters 2, 4, 8

Scanning LiDAR (SSL)

adopting SSL (a method of measurement using

and 9, Annexes

just one scanning LiDAR (SL)) for indirect

A, B and C

measurement (remote sensing) as the windmeasurement method.
 It is possible to install the equipment on land andperform offshore measurement, but themeasurable range is limited.
6

Measurement using This chapter summarizes the requirements whenvertical LiDAR (VL)

adopting VL for indirect measurement (remote

Chapters 2, 8,
and 9

sensing) as the wind measurement method.
 To perform offshore measurement, it is necessary
to install the equipment on a fixed or floating
platform.
7

Measurement using a This chapter summarizes the requirements when

Chapters 2, 6, 8

Floating LiDAR System

adopting an FLS equipped with VL (a method ofand 9, Annex D(FLS)

measurement using VL installed on a floating
buoy, etc.) for indirect measurement (remotesensing) as the wind measurement method.
 This can be installed in a wide area ranging fromshallow sea areas to deep sea areas.

28Complementation methods
and accuracy verification

complementing the measurement data when using

when measurement data

any of the measurement methods in Chapters 3 toare missing9

 This chapter summarizes the requirements for

Reporting

Chapters 2, 3 to7, and 97.
 This chapter summarizes the contents included in

Chapters 2 to 8

reports on wind measurement and wind condition
evaluation.
A

Hard target adjustment

 This section summarizes the method of hard target
adjustment for RSD.

B

Pre-deployment
verification of accuracy

C

Data acquisition rate
check

D

Example of FLS
installation work

 This section summarizes the method of the predeployment verification of RSD accuracy.
 This section summarizes the method of checking
the RSD data acquisition rate.
 This section summarizes of example of FLS

Chapters 4 and
5Chapters 4 and
5Chapters 4 and
5Chapter 7

installation work

1.3 Relevant laws and regulations
1.3.1 Relevant laws, regulations and ordinances, and their interpretations and explanations
 Ministerial Ordinance Prescribing Technical Standards for Wind Power Generation Facilities (Ordinanceof the Ministry of International Trade and Industry No. 53 of 1997)
 Ministerial Ordinance Prescribing Technical Standards for Electric Facilities (Ordinance of the Ministryof International Trade and Industry No. 52 of 1997)
 Interpretation of Technical Standards for Wind Power Generation Facilities (Ministry of Economy, Tradeand Industry, No. 20140328, Bureau of Commerce No. 1, 2014)
 Annotations to the Ministerial Ordinance Prescribing Technical Standards for Wind Power Generation
Facilities and its Interpretation (2021, Ministry of Economy, Trade and Industry, partially revised on June21, 2021)
 Regulation for Enforcement of the Port and Harbor Act (Ministry of Transport Order No. 98 of 1951)
 Ministerial Ordinance Prescribing Technical Standards for Port Facilities (Ordinance of the Ministry ofLand, Infrastructure, Transport and Tourism No. 15 of 2007)
 Public Notice Establishing Necessary Matters Concerning Standards for Publicly Offered Facilities, etc.
and Their Maintenance and Management Methods (Public Notice of the Ministry of Land, Infrastructure,
Transport and Tourism No. 858 of 2016)
 Public Notice Prescribing Details of Technical Standards for Port Facilities (Public Notice of the Ministryof Land, Infrastructure, Transport and Tourism No. 395 of 2007)
 Regulation for Enforcement of the Act on Promoting the Utilization of Sea Areas for the Development ofMarine Renewable Energy Power Generation Facilities (Ordinance of the Ministry of Land, Infrastructure,
Transport and Tourism and Ministry of Economy, Trade and Industry No. 1 of 2019) Public Notice Establishing Necessary Matters Concerning Standards for Marine Renewable Energy Power
Generation Facilities and Their Maintenance and Management Methods (Ministry of Land, Infrastructure,
Transport and Tourism Notice No. 388 of 2020)3

 Technical Standards for Floating Offshore Wind Power Generation (Safety Policy Division, Maritime
Bureau, Ministry of Land, Infrastructure, Transport and Tourism, No. 194, 2020)
1.3.2 Japanese standards and guidelines related to laws and regulations
 Recommendations for Loads on Buildings (2015, Architectural Institute of Japan)
 Guidelines and explanation for the design of support structures of wind power generation facilities (2010,
Japan Society of Civil Engineers) Recommendations for Design of Building Foundations (2019, Architectural Institute of Japan)
 Recommendations for Design of Chimney Structures (2007, Architectural Institute of Japan)
1.3.3 Technical standards
 JIS C 1400-1: 2017 Wind Energy Generation systems -- Part 1: Design requirements
 IEC 61400-1:2019 Wind energy generation system - Part1: Design requirements
 IEC 61400-3-1:2019 Wind energy generation system - Part3-1: Design requirements for offshore windturbines
 IEC TS61400-3-2:2019 Wind energy generation system - Part3-2: Design requirements for floating
offshore wind turbines
 JIS C 1400 -12 -1: 2010 Wind turbines- Part 12-1: Power performance measurements of electricity
producing wind turbines
 IEC 61400-12-1:2017 Wind energy generation system – Part12-1: Power performance measurements ofelectricity producing wind turbines
 IEC 61400-50-1(RFDIS) Wind energy generation system – Part50-1: Application of meteorological mast,
nacelle and spinner mounted instruments
 IEC 61400-50-2(TPUB) Wind energy generation system – Part50-2: Application of Ground Mounted
Remote Sensing Technology
 IEC 61400-50-3:2022 Wind energy generation system – Part50-3: Use of nacelle-mounted lidars for windmeasurements
 IEC 61400-50-4(ACD) Wind energy generation system – Part50-4: Use of floating lidars for windmeasurements
1.3.4 Guidelines and recommended standards
 MEASNET, Evaluation of site-specific wind conditions, Version 2, April 2016.
 IEA Wind Expert Group Report on Recommended Practices 18. Floating LIDAR systems, First Edition,
2017.
 Carbon Trust Offshore Wind Accelerator Roadmap for the Commercial Acceptance of Floating LiDAR
Technology, Ver.2.0, 2018.
 Carbon Trust, Remote Wind Measurements Offshore Using Scanning LiDAR Systems, 2014.
 NEDO Guidebook of Bottom Fixed Offshore Wind Turbine Introduction, 2018.
 NEDO Guidebook of Floating Offshore Wind Turbine Technology, 2018.
 Ministry of Economy, Trade and Industry Manual for the Introduction of Floating Offshore Wind Power
4

Generation, 2019.
 Committee on Study of Developing Offshore Wind Power Generation Facilities Official Explanation ofTechnological Standards for Offshore Wind Power Generation Facilities, 2020
 Ministry of Land, Infrastructure, Transport and Tourism Maritime Bureau Technical Standards for
Floating Offshore Wind Power Generation Facilities, 2020.
 Japan Coast Guard Guidelines for the Installation and Management of Navigational Aids, November 2021.
 Nippon Kaiji Kyokai NKRE-GL-WFC01 Wind Farm Certification Onshore Wind Power Plant Edition,
July 2021 edition
 Nippon Kaiji Kyokai NKRE-GL-FOWT01 Guidelines for Floating Offshore Wind Power Facilities,
December 2021 edition.

1.4 Terms and abbreviations
The definitions of the main terms and abbreviations used in this Guidebook are given in Table 1.2 and Table
1.3, respectively.
Table 1.2 Terms
Term
Wind shear
Wind shear exponent
Wind shear law
Wind profile

Wake

Aerosol
OffsetCup anemometer

Carrier to noise ratio

Definition and description
The change in wind speed on a plane perpendicular tothe direction of the wind.
The exponent of the exponential law (power law) for
wind shear.
The mathematical representation assumed for changes
in wind speed relative to the height above ground.
Usually the logarithmic law or exponential law is used.
Vertical distribution of wind speed.
The flow with velocity defects that occurs in the flow
behind an object. In the field of wind power generation,
it often refers to the flow that occurs behind a windturbine for power generation. If a meteorological mastis in a position where it enters a wind turbine wake, it isaffected by a decrease in the speed and an increase in
the turbulence.
A mixture of small liquid or solid particles suspended ina gas and the surrounding gas.
Offset b of the linear equation (y = ax + b) for
correlation analysis
Hemispherical or conical cups (wind cups) arranged inthree or four directions around a vertically supported
axis of rotation. It rotates when the wind hits the windcups and the wind speed is measured by counting therotations. In the field of wind power generation, thestandard is the measurement method using a cup
anemometer.
An indicator of the quality of the carrier (carrier wave)of an optical or electrical signal, also referred to as the
CN ratio. The power of the carrier divided by the powerof the noise is usually expressed in dB, with higher
values indicating better quality.

5

Idiom or synonym
Wind shear, shear
Exponent, αHeight distribution ofwind speed

Intercept

TermElevation angle
Radial velocity
Ambient turbulence intensity

Scanning lidar

Sector size
Double bias correction

Dual scanning lidar

Hard target
Hub height

Filtering

Meteorological mast

Floating lidar system

Wind vane

Vertical lidar

Environmental condition

Definition and description
The angle formed by the installation surface of thescanning LiDAR and the line connecting the laser lineof sight and the measurement point.
The component of the wind velocity in the direction of
the laser light emission.
The value that is the standard deviation of the main
wind direction component of the wind speed divided by
the wind speed.
The component of the wind velocity in the direction of
the laser light emission (the radial velocity) is measured
by measuring the Doppler shift of the waves reflected
due to aerosols in the air, and then the horizontal windspeed is calculated from the results of radial velocity
measurements in a plurality of directions. A scanning
LiDAR measures the wind speed by scanning the laser
in the horizontal direction or the vertical direction.
The azimuth (sector) angle when the azimuth angles of
the wind direction are divided by a certain angle.
One of the models used in the MCP method for
turbulence intensity.
A measurement system that uses two scanning LiDAR
units to determine the wind velocity vector from theradial velocity at the intersection of two lasers. It is also
possible to measure multiple points in the height
direction.
A physical target used to determine the intersection of
the two lasers in dual scanning LiDAR.
The height of the center of the swept area of a windturbine rotor above the ground.
The analysis process in which the observer determines
whether the radial velocity is valid or invalid, separatelyfrom the status information. The abnormal values are
sorted from the radial velocity or CNR output raw
values from the LiDAR. The standard deviation andquantile values for 10 minutes are used to judge theabnormal values.
A freestanding mast that is installed for themeasurement of wind speed and direction. Cupanemometers and wind vanes, etc., are installed at
multiple heights. Refer to IEC 61400-12-1 and the
Measnet guidelines for the method of equipment
installation.
A system in which a vertical LiDAR is installed on a
floating buoy, etc.
A vertically supported rotating shaft that is equippedwith a horizontal bar that has a weight and a plate
installed at its two ends. It is an instrument formeasuring wind direction.
The component of the wind velocity in the direction of
the laser light emission (the radial velocity) is measured
by measuring the Doppler shift of the waves reflected
due to aerosols in the air, and the horizontal wind speed
is calculated from the results of radial velocity
measurement in a plurality of directions. A vertical
LiDAR rotates the laser around an upward vertical axis.
Characteristics of the environment (wind, altitude,
temperature, humidity, etc.) that may affect the
behavior of the wind turbine.

6

Idiom or synonym

Degree of turbulenceWind direction bin
width

Hub height

Weather mast,
weather measurement
mast, windmeasurement towerTerm
Flow inclination angle
Slope
Verification

Calibration

Swept area

Key performance indicator (KPI)

Obstacles
Accuracy
Atmospheric stability

Surface roughness

Roughness length

Annual average

Annual average wind speed
Uncertainty

Wind speed distribution

Mean wind speed

Flow model
Turbulence intensity
Turbulence standard deviation

Definition and description
The inclination of the air current to the horizontal.
The slope a of the linear equation (y = ax + b) for
correlation analysis.
To confirm that the specified requirements are satisfied
by providing objective evidence. For example, that the
manufacturer’s specifications are satisfied.
The act of comparing the value from a standard
measuring instrument with the value indicated by themeasuring instrument being evaluated to determine howmuch variation exists.
The plane drawn by the rotor during one revolution
projected perpendicular to the direction of the wind.
A quantitative indicator for the measurement andmonitoring of the degree to which the performancetargets for a device are being achieved, in order toevaluate the performance of that device.
The objects such as buildings and trees that shield thewind and cause distortion in the airflow.
The degree of agreement between the measurement
results and the true values of the item being measured.
The degree to which the atmosphere is affected by thetemperature difference between the upper and lower
layers.
This means the roughness of the ground surface.
Surface roughness is divided into the four categories of
I to IV.
The extrapolated height at which the mean wind speed
is zero when it is assumed that the vertical wind profile
varies logarithmically with respect to height.
This is an average calculated from measurement data
sets with a sufficient amount of data collected over a
sufficient period of time, and can be used to estimate
the expected value of the item being measured. It is
desirable that the period for calculating the average be
an integral multiple of whole year units, in order tosmooth out transient effects such as seasonal
differences.
The wind speed averaged according to the definition of
the annual average.
A parameter that characterizes the variability of values
that are reasonably tied to a target quantity.
A probability distribution function used to describe the
distribution of wind speeds over a long period of time.
The functions that are frequently used are the Rayleighdistribution function and Weibull distribution function.
The statistical average of instantaneous values of windspeed averaged over a given period of time, which may
range from seconds to years.
A model that represents the motion of airflow
numerically.
The ratio of the standard deviation of the wind speed tothe mean wind speed.
The standard deviation of the main wind direction
component of the wind speed.

7

Idiom or synonym
Blowup angle, flow
tilt angle
Slope
Verification

Frequency
distribution by windspeed class, windspeed distribution

Wind condition
simulation, windcondition analysis
Degree of turbulenceTerm

PPI (Plan-Position-Indicator)
measurement

Roll angle
Tilt angle

Definition and description
A method of fan-shaped scanning in which the elevation
angle is fixed and the azimuth angle is varied. There isalso RHI (Range Height Indicator) measurement. RHI
measurement is a method of scanning in which theazimuth angle is fixed and the elevation angle is varied.
PPI scans are used to obtain high resolution samples in
the azimuth angle direction. RHI scans are used toobtain high resolution samples in the elevation angle
direction.
The angle of rotation about the north-south axis when ascanning LiDAR is installed on a platform.
The angle of rotation about the east-west axis when ascanning LiDAR is installed on a platform.

Idiom or synonym

Table 1.3 Abbreviations
Abbreviation
CNR
DBC
DBS
DSL
FLS
GNSS
KPI
LiDAR
MM
MCP
MEASNET
MSL
OWA
PPI
RHI
RSD
SL
SSL
TSL
VL

Definition
Carrier to Noise Ratio
Double Bias Correction
Doppler Beam Swinging
Dual Scanning LiDAR
Floating LiDAR System
Global Navigation Satellite System
Key Performance Indicator
Light Detection and Ranging
Met Mast
Measure-Correlate-Predict
Measuring Network of Wind Energy Institutes
Mean Sea Level
Offshore Wind Accelerator
Plan-Position Indicator
Range Height Indicator
Remote Sensing Device
Scanning LiDAR
Single Scanning LiDAR
Triple Scanning LiDAR
Vertical LiDAR

8

Term

Global Navigation Satellite System
Key Performance Indicator
LiDAR
Meteorological mast
MCP (Measure-Correlate-Predict) method
Mean Sea Level
Horizontal scan
Vertical scanRemote Sensing Device

2. Wind measurement and wind condition evaluation
2.1 Wind measurement items and evaluation items
For the planning of offshore wind farms, Table 2.1 shows the items that are to be evaluated based on
offshore measurements as the wind conditions necessary for the prediction of the energy yield and for thewind turbine design. The measurement equipment that can be used for the measurement of the offshore windconditions is (a) meteorological masts (MM) and dual scanning LiDAR (DSL), and (b) single scanning
LiDAR (SSL), vertical LiDAR (VL) and floating LiDAR systems (FLS). In order to evaluate the items
described in Table 2.1, the measurement of the offshore wind is performed with either of (a) or (b) shown in
Table 2.2, or with a combination thereof. Measurement data are recorded continuously and statistical values
based on the 10-minute values obtained from the measurement data are used as the wind condition evaluation
data necessary for the prediction of the energy yield and the wind turbine design.
Table 2.1 Wind condition evaluation items
necessary for power generation prediction and wind turbine design
Evaluation item

Measurement
devicesthat can be used*1

Explanation

Mean wind speed

Annual average wind speeds per direction and in all(a), (b)directions
Wind speed distribution

Weibull parameters direction and in all directions(a), (b)Appearance frequency

Appearance frequency distribution per direction(a), (b)Ambient turbulence intensity per direction and in all(a)distribution by wind direction
Turbulence intensity

directions (90% quantile)
Wind shear exponent

Wind shear exponent per direction and in all directions(a), (b)Flow inclination angle

Flow inclination angle per direction and in all directions- *2*1: Equipment that is judged to be technically usable at the current time.
*2: In the case of offshore measurement, 0 degrees is acceptable.

Table 2.2 Wind measurement items(a) Meteorological Mast (MM) and Dual Scanning LiDAR (DSL)
Measurement item

Statistical value

Number of measurement points

Wind speed

Mean, standard deviation

Multiple heights (Three or more heights)

Wind direction

Mean value

Multiple heights (Three or more heights)(b) Single Scanning LiDAR (SSL), Vertical LiDAR (VL) and Floating LiDAR System (FLS)
Measurement item

Statistical value

Number of measurement points

Wind speed

Mean value

Multiple heights (Three or more heights)

Wind direction

Mean value

Multiple heights (Three or more heights)

9

The increase in the size of wind turbines has made it necessary to observe the wind conditions at high heights,
and reasons such as the expensive cost of using a meteorological mast for measurement at high heights havemeant that the use of remote sensing devices (hereinafter referred to as RSD) is advancing. In particular, smaller
sizes and lower costs have been achieved for LiDAR equipment that measures the wind with a laser, and this isbecoming the main equipment used. The LiDAR technology measures the wind by irradiating the aerosols in
the air with a laser and measuring the laser scattering.
The RSD covered in this Guidebook are dual scanning LiDAR (DSL), single scanning LiDAR (SSL), vertical
LiDAR (VL) and floating LiDAR systems (FLS) that have VL installed on a floating platform. DSL means
measurement by two scanning LiDARs, and SSL means measurement by one scanning LiDAR.
The use of three scanning LiDARs in triple scanning LiDAR (TSL) makes it possible to observe threecomponents, so, in principle, it is possible to measure the turbulence intensity. However, if the elevation angle
is reduced to the threshold value or less, then even just two scanning LiDARs can measure the turbulence
intensity with high accuracy (two components in the horizontal plane), so this Guidebook deals only with DSL
and just introduces reference documents for TSL1).
Figure 2.1 shows examples of the RSD measurement modes. It shows the PPI measurement mode, which isscanning in the azimuth angle direction with the elevation angle fixed, RHI measurement mode, which isscanning in the elevation angle direction with the azimuth angle fixed, fixed measurement mode, in which boththe elevation angle and the azimuth angle are fixed, and DBS measurement mode, where a vertical profile isscanned for each of the north, east, south, and west directions.

Figure 2.1 Examples of the RSD measurement modes10

At present, the technologies that can measure with sufficient accuracy for the turbulence intensity evaluationnecessary for wind turbine design are a cup anemometer installed on a meteorological mast and DSL. To
perform the turbulence intensity evaluation that is necessary for wind turbine design, examples include an
offshore meteorological mast satisfying 2/3 or more of the hub height, an offshore meteorological mast that is
at less than 2/3 of the hub height combined with a VL installed on the mast platform, and offshore measurement
using DSL installed on land.
Measurement errors occur in the measurement of turbulence intensity by VL, so it is necessary to correct thisby the method proposed by Yamaguchi et al2).
With an FLS, in addition to the turbulence intensity errors of vertical LiDAR, there is also an effect from theswaying motion, so the measurement error becomes larger than that of a cup anemometer. Several previous
studies have been conducted on motion compensation to eliminate this effect3) -4). However, correction isnecessary for the same reason as for the VL described above.
There is also a problem with the accuracy of turbulence intensity measurement using SSL.
The wind condition evaluation items necessary for the prediction of the energy yield and the wind turbine
design are as shown in Table 2.1. Together with these, it is also desirable to include energy density distribution
per direction.
For the measurement heights, at least three heights must be used in order to properly evaluate the wind shear
on the wind turbine rotor plane.
From the viewpoints of reducing the uncertainty in the calculation of wind measurement data statistics,
redundancy (measures in case of failure, etc.), and the evaluation of atmospheric stability, it is better to have alarge number of measurement points. However, increasing the number of measurement devices increases thepower consumption and leads to an increase in the measurement costs, so the information given here shows theminimum number of measurement points necessary.
Temperature and air density are also important in the wind condition evaluation necessary for the predictionof the energy yield and the wind turbine design, but this Guidebook only covers wind measurement.
Table 2.3 shows examples of wind measurement items on offshore meteorological masts in Japan. At all of
the measurement sites, vertical LiDAR measurements were also conducted adjacent to the meteorological mast.
At the Choshi meteorological mast, an SSL measurement demonstration was conducted. In this project, thedemonstration of measurement by DSL, SSL and an FLS is being carried out.

11

Table 2.3 Examples of wind measurement items on offshore meteorological masts in Japan
NEDO
Measurement
Mutsu Ogawara offshore
item
meteorological mast
Cup anemometers:

Wind
speed

NEDO
Choshi fixed-bottom
meteorological mast
Cup anemometers:

NEDO
METI
Kitakyushu fixed-bottom Fukushima floating typemeteorological mast
meteorological mast
Cup anemometers:

Cup anemometers:- 63 m high, two directions- 90 m high, three directions- 80 m high, two directions- 60 m high, three directions- 59 m high, one direction- 80 m high, three directions- 70 m high, two directions- 50 m high, three directions- 50 m high, one direction- 70 m high, three directions- 60 m high, two directions- 40 m high, three directions- 25 m high, four directions- 60 m high, three directions- 50 m high, two directions

Ultrasonic anemometer:- 61 m high, one direction- 50 m high, three directions- 40 m high, two directions- 40 m high, three directions- 30 m high, two directions- 30 m high, three directions- 20 m high, one direction
Ultrasonic anemometers:

Ultrasonic anemometers:- 80 m high, one direction- 60 m high, one direction- 80 m high, one direction- 40 m high, one direction- 60 m high, one direction- 20 m high, one direction- 40 m high, one direction
Wind vanes:

Wind vanes:

Wind vanes:- Apex- 95 m high, one direction- 80 m high, one direction- 50 m high, one direction- 90 m high, three directions- 70 m high, two directions- 60 m high, three directions- 80 m high, three directions- 60 m high, one direction- 50 m high, three directions- 70 m high, three directions- 50 m high, two directions- 40 m high, three directions- 60 m high, three directions- 40 m high, one direction

Ultrasonic anemometer:- 61 m high, one directionWind
direction

Wind vanes:- 61 m high, one direction- 50 m high, three directions- 40 m high, three directions- 30 m high, two directions
Ultrasonic anemometers:- 30 m high, three directions- 80 m high, one direction- 20 m high, one direction- 60 m high, one direction

Ultrasonic anemometers:- 80 m high, one direction- 60 m high, one direction- 40 m high, one direction

12- 40 m high, one direction- 20 m high, one direction

2.2 Representativeness of wind conditions and selection of measurement points
Conduct offshore wind measurement at one or more offshore points that are representative of the plannedsite, either by using cup anemometers and wind vanes installed on meteorological masts, or by using a remotesensing device (RSD) that has the point(s) as the measurement position(s). Use measurement devices thathave had their accuracy verified in advance.
The period of the offshore wind measurements must be a sufficient period to evaluate annual statistics andmust be at least one year, to allow for seasonal effects. In addition, in order to obtain the statistical values
based on 10-minute values that are the wind condition evaluation data necessary for the prediction of theenergy yield and the wind turbine design, the measurement height used must be 2/3 or more of the plannedwind turbine hub height, and the measurement must be conducted at a total of three or more heights in orderto properly evaluate wind shear. One measurement point can represent the planned wind turbines within 10
km of that point.
It is necessary for the wind measurement plans for a site to provide enough quality information for the power
generation and wind condition evaluations for all the wind turbines in the wind farm. The measurement devices
used must have been verified in advance in accordance with the existing standards (including documents underdevelopment). Table 2.4 shows the IEC standards for wind measurement by various measurement devices. The
IEC standards for wind measurements were published in the 61400-12 series, and the text of the 61400 series
was reconstructed. The only document in Table 2.4 that has been issued at the current time is IEC61400-50-3.
There is no previous applicable standard for prior accuracy verification by scanning LiDAR, so follow thisGuidebook.
Table 2.4 IEC standards for wind measurement
Measurement device

Fixed platform

Floating platform

Meteorological mast

IEC61400-50-1-

Vertical LiDAR
RSD

IEC61400-50-2 *1

IEC TS61400-50-4

LiDAR mounted on nacelle

IEC61400-50-3-

Scanning LiDAR--*1: The scope of this is RSD installed on land, so it is not limited to vertical LiDAR.

It is recommended that the wind measurement planning (measurement devices, heights, positions, sensor
arrangements, etc.) be carried out based on analysis of the site-specific influencing factors, which is influencing
factors such as the topographic factors, geographical factors, and meteorological factors of the planned windfarm site.
When predicting the wind conditions at each wind turbine position in the planned wind farm, if the distancefrom the wind turbine position in the wind farm to the measurement point is within the representative radius,then it is assumed that it will be within the range of allowable uncertainty.
When using RSD, it is desirable to use the planned hub height as the measurement height to obtain statisticalvalues based on 10-minute values, which are the wind condition evaluation data necessary for the prediction of
the energy yield and the wind turbine design. In addition, for the measurement heights added for the evaluation13

of wind shear, it is desirable to perform measurements of an appropriate height within the rotor plane above andbelow the hub height of the planned wind turbine. However, the specific heights are set according to the situationof the field measurements.
Although the representative radius is considered to be greatly dependent on the site-specific conditions, thevalue of the representative radius defined by Measnet, etc., for flat topography (10 km) is applied offshore inthis document. However, in a sea area close to the coastline, the spatial variation of wind conditions increases
due to changes in surface roughness and the influence of the topography in the coastal area, so it is thought thatthe representative radius becomes smaller than 10 km. Therefore, it is necessary to consider these factors when
deciding the number of wind measurement points for a planned wind power plant.
2.3 Measurement data evaluation
1)

For the wind condition measurement data to obtain the statistical values based on 10-minute values thatare the data used as the wind condition evaluation data necessary for the prediction of the energy yieldand the wind turbine design, the wind measurement data should be data for a period of one year or amultiple thereof, and the effective data rate used should be 95% or more.

2)

If there is a period in which the wind condition measurement data is missing or shows abnormal values,
such as due to a failure of the measurement devices or weather conditions, etc., and the conditions of 1)
above cannot be satisfied, perform data compensation using measurement data. However, if
compensation using measurement data is performed, verify the accuracy of that complementation andshow the validity of the complemented data.

The evaluation items are as shown in Table 2.1.
The details of the complementation method, the accuracy verification method for the data after
complementation, the key performance indicator (KPI) for the accuracy verification, and the acceptance criteria
are given in Chapter 8. Compared to meteorological masts, RSD are more affected by weather conditions andtend to have a lower effective data rate.

14

3. Measurement using offshore meteorological masts
3.1 Selection of measurement points
In the case of measurement using offshore meteorological masts, in addition to the details in item 2.2,
attention must also be paid to the following matters.
 If the topography and surface roughness are not uniform in the area around the site, the measured values
at the measurement point may be affected differently from the wind turbine position. Appropriate priorconsideration should therefore be made, such as by conducting airflow analysis at the stage of themeasurement point selection.
 If measurements must be made in the vicinity of an existing wind turbine that is in operation, select apoint that is not affected by the wake of that wind turbine.
If the planned site is close to the shore, it may be affected by topography such as coastal cliffs and coastal
terraces. In such a case, the representative radius of 10 km may not be valid, so it is desirable to consider the
installation site in advance with airflow analysis.
According to JIS C 1400-1:2017, when considering the influence of the wake of adjacent wind turbines, if
the distance between the wind turbines is 10 times or more the rotor diameter of the wind turbine, the influenceof the wake is not taken into account. This is one indicator that can be used for the separation distance when
considering the effect of the wake. However, for offshore sites, there is a risk that the wake may have an effectat points further away than the effect on land, so this point should be kept in mind when considering the effectsof wake. Figure 3.1 shows the installation site of the offshore meteorological mast on the breakwater of the
Mutsu Ogawara Port as a reference.

• Offshore meteorological mast (63 m asl)

• Vertical LiDAR

Figure 3.1 Example of offshore wind measurement point (Mutsu Ogawara Port)15

3.2 Measurement of wind speed and wind direction
The measurement of wind speed is carried out by a cup anemometer or an anemometer for which theaccuracy is guaranteed to be equivalent to a cup anemometer. The cup anemometers used must be calibrated
before the measurement period. Perform the calibration of cup anemometers according to the procedure in
JIS C 1400-12-1:2010, or in a procedure recognized as equivalent, and attach the calibration results to thereport.
Install a cup anemometer at a position that is not less than 2/3 of the hub height from the ground surface.
If this is difficult, measurement in combination with RSD will be necessary. However, even in that case, thecup anemometer should be installed at the highest position possible. In order to evaluate the vertical profileof the wind speed at the site, add two or more anemometers below the topmost anemometer at intervals of
approximately 10 m.
In the installation of anemometers on the measurement mast, the attachment must be in a manner thatminimizes the effects on the anemometer from the meteorological mast and the boom. A lightning rod must
be installed in a position where it will not affect the anemometers.
For the wind speed, measure the 10-minute mean value and standard deviation. The sampling frequency
used should be 1 Hz or higher.
In cold regions where the temperature of the planned site falls below zero, in order to maintain the response
characteristics specified in the anemometer regulations, it is necessary to take measures against freezing,such as the installation of heaters.
Measure the wind direction with a wind vane. In the installation of wind vanes on the measurement mast,
the attachment must be in a manner that minimizes the effects on the wind vane from the meteorologicalmast and the boom.
For the wind direction, measure the 10-minute mean value. The sampling frequency used should be 1 Hzor higher.
It is desirable that the installation of anemometers and wind vanes is performed in accordance with JIS C
1400-12-1:2010 Annex G. The anemometer at the top of an measurement tower is attached to a vertical circulartube of the same external shape as that at the time of calibration. For the direction of the booms to whichanemometers are attached, in order to properly evaluate wind shear, it is desirable that all the booms are installedin the same direction. It is desirable to install an anemometer as a backup for the anemometer installed at the
top of an measurement tower. The backup anemometer should either be mounted on another boom at the sameheight, or installed at a height below the boom with a separation of at least 4 m.
For the installation of booms, it is recommended that the boom be installed in a direction 45° from the main
wind direction on a cylindrical mast, and at 90° on a truss structure. When the wake effect of the measurement
tower is large, it is desirable to install booms in three directions or more to conduct the measurement. It is betterto avoid installing other instruments on a boom where an anemometer is installed. When a wind vane is installed,
azimuth determination is important in order to direct the north mark to the accurate azimuth.
It is desirable to conduct wind measurements in cold regions in accordance with IEC 61400-12-1:2017
Annex O Power performance testing in cold climate.
When installing a meteorological mast, it is necessary to appropriately evaluate the external conditions at16

the installation site, and to confirm that the meteorological mast, its supporting structure, platform, and frame
are structurally safe against loads due to extreme wind and extreme wave height, and against loads due towind and wave fluctuations.
Wind measurements at sea are more likely to be affected by salt damage, wave splashing, and sandscattering than those on land, so higher weather resistance is required. Measurement sensors, cables, loggers,
and power supply systems (including fuel cells) must have adequate measures implemented for waterproofing,
dustproofing, and protection against salt damage (such as shielding, painting, and insulation strengthening),
and it is desirable to prepare replacement items to enable a rapid response in the event of a failure.
For the power supply system, assume that access difficulties will occur due to stormy weather, andappropriately implement suitable redundancy measures and emergency response measures.
After the end of an measurement period, the anemometer should be recalibrated as necessary. If the resultof the recalibration is different from the calibration result before the start of the measurement period, perform
a comparison with other anemometers installed on the mast to identify the time when the difference began toappear. When this is complete, narrow down the evaluation period for the measurement data to the period
when the measurement performance of the anemometer is within the allowable uncertainty. If recalibration is
not performed, an alternative method is to check that the performance of an anemometer has not deteriorated
during the entire measurement period by comparing it with other anemometers installed nearby. This isverified by evaluating any significant correlation changes over time.
Figure 3.1 shows the installation example of the offshore meteorological mast on the breakwater of the
Mutsu Ogawara Port as a reference.

Figure 3.2 Example of offshore meteorological mast (Mutsu Ogawara Port)17

3.3 Data analysis
Evaluation of the measurement results is conducted in accordance with the items in Table 2.2.
Before performing analysis, perform filtering to remove any abnormal values and calculate the effective
data rate. Indicate the data removal method and criteria applied at the time of the calculation in the report.

When the wind measurement is affected by the wake of the tower, appropriately select the anemometers andwind vanes to be used for the analysis according to the wind direction. Examples of methods for selecting theanemometers installed on offshore wind measurement towers include the data processing performed at theEgmond aan Zee offshore wind farm in the Netherlands5), the processing performed at FINO3 in Germany6),
and the processing performed at the site off Choshi, which was evaluated with reference to these two examples7).

18

4. Offshore measurement using Dual Scanning LiDAR
4.1 Selection of measurement points
4.1.1 Selection of measurement points
Decide the measurement points based on the wind turbine layout and with consideration of therepresentative radius and the data acquisition rate at the offshore point.
The measurement point in DSL measurement is the point where the laser beams from two SL units intersect.
Install the SL in locations where there are no obstacles such as structures and trees along the line of sight
between the installation location of each SL and the measurement point.
For the measurement heights, in order to properly evaluate the wind shear on the wind turbine rotor plane,
perform measurements for a total of at least three heights.
It is desirable that the angle formed by the two lasers is between 30° and 150°8),9), and 90° is ideal.
For the obstacles in the vicinity, care should also be taken to avoid the laser entering the range of motion of
objects that are moved by the wind, such as electric wires, guy wires, and tree branches. Figure 4.1 shows anexample of an offshore wind measurement point using DSL (Mutsu Ogawara Port).
The effective data rate depends on the measurement distance and the weather conditions, so it is preferable
to determine the measurement distance based on the performance of the equipment and the past weather data(such as fog, rain, snow, and aerosols) for the site. The data acquisition rate decreases in dense fog, heavy snow,
snowstorms, and heavy rainfall21).

SL2.54 km64°

Measurement
point SL

1.61 km
SL
Figure 4.1 Example of an offshore wind measurement point using DSL (Mutsu Ogawara Port)19

4.1.2 Installation of equipment
When installing equipment, ensure that the levelness is maintained. The levelness of the equipment mustalso be maintained during the measurement period.
A slight deviation in the elevation angle of the laser causes a large deviation in the measurement height, so it
is necessary to design the platform on which the equipment is installed so as to maintain the levelness during
the measurement period. In Japan in particular, it is necessary to consider the situation regarding earthquakes
in the local area.
Also, when installing equipment on a platform , perform adjustment so that the tilt angle and roll angle on
the inclinometer inside the equipment become less than ±0.02°, and confirm that these are being maintained
during the measurement period. The tilt angle and roll angle definitions are shown in Figure 4.2. (Positive andnegative may be reversed, depending on the model.) Fix the equipment to the platform firmly so that it does notshift during the measurement period.
It is desirable to install fences around the equipment and platform so that animals and people other thanrelated staff cannot enter.
If the planned site is an area where snow accumulates, set an appropriate platform height based on past
weather records.

Figure 4.2 Definitions of RSD roll and tilt

4.1.3 Hard target adjustment
Set the azimuth angle and elevation angle for the laser irradiation from an SL in accordance with theprocedures in Annex A and include the results of the verification in the report.

In order to set the azimuth angle and elevation angle accurately, use GNSS surveying equipment to measure
the latitude, longitude and height of the SL installation site and the fixed objects (hard targets) to be used foralignment. It is desirable to use three or more hard targets.
If the distance from the SL installation site to a hard target is too short, it is not possible to maintain sufficient
positional accuracy. The guideline is to use a distance of around 1 km. The surveying instruments selected20

should have sufficient measurement accuracy. When the laser beam of the SL hits a fixed object, a strong CNR(carrier-to-noise ratio) value is observed. The offset value to be added to the settings on the SL for the azimuth
angle and elevation angle can be calculated by checking the deviation between the azimuth angle and elevation
angle of the hard target outputted by SL and the azimuth angle and elevation angle of the hard target (truevalues) when viewed from the actual SL installation location. This is called hard target adjustment.
4.2 Measurement of wind speed and wind direction
Conduct wind speed and wind direction measurement with devices that have had their accuracy verified inadvance and the data acquisition rate confirmed. Perform the pre-deployment verification of accuracy inaccordance with the procedures in Annex B and attach the results of the verification to the report. Perform theconfirmation of the data acquisition rate in accordance with the procedures in Annex C and attach the resultsof the confirmation to the report. After the end of the measurement period, confirm that the measurement
accuracy has been maintained.
For the measurement height, in order to evaluate the wind shear at the wind turbine rotor plane, set theelevation angle so that measurements are made at three points near the hub height, the rotor top tip height,
and the rotor bottom tip height. Set the time intervals used in the switching between each measurement height(or elevation angle) with consideration of the accuracy and the effective data rate. Perform timesynchronization so that the two SLs simultaneously observe the same measurement height.
For the wind speed, measure the 10-minute mean value and standard deviation. The SL sampling frequency
for the radial velocity should be about 1 Hz or more.
Also, in cold regions where the temperature of the planned site falls below zero, implement measures againstsnow accumulation and freezing.
It is desirable for the elevation angle for measurement using DSL to be within 5°. Set the measurement heightwith consideration of the measurement distance and the heights of the hub, the rotor upper tip and the rotor
bottom tip on the planned wind turbine.
The data acquisition rate and the measurement accuracy depend on the measurement settings, so the settings
for the measurements at the planned site should be the same as the measurement settings (for range gate,
integration time, and switching time of measurement heights) used in the pre-deployment verification of
accuracy. If the measurement distance or the angle between the two lasers is significantly different between the
pre-deployment verification of accuracy and the measurements at the planned site, then there is a risk that theaccuracy at the time of the verification will not be guaranteed.
At present, there are cases in which just the standard measures on SL against snow accumulation and freezing(such as the wiper operation settings and wiper washer fluid concentration) do not have a sufficient effect, so it
is hoped that solutions will be found in the future. Conduct periodic monitoring and corrective action to ensurethat there are no long periods of missing measurement data in the winter.

21

4.3 Data analysis
4.3.1 Flow of data analysis
Perform the evaluation of the measurement results in accordance with the items related to wind speed andwind direction in Table 2.1.
Clearly indicate the procedure for calculating the 10-minute average horizontal wind speed, wind direction,
and wind speed standard deviation from the radial velocity obtained from each SL. Also include filtering in
the procedure.
An example of the data analysis procedure is shown in Figure 4.3. When there is more than one filtering
process, clearly indicate them so that it is possible to know their order.

Figure 4.3 Example flowchart of data analysis procedure224.3.2 Filtering
In order to calculate the 10-minute average horizontal wind speed, wind direction, and wind speed standard
deviation, perform filtering to remove abnormal values.
Remove data from the measurement data set if it is data from a time when the equipment was in an abnormal
state, from a time when the CNR value exceeded the threshold value, from a time when the radial velocities
from the two SL units were not simultaneous, from a time when the instantaneous value of the radial velocity
exceeded 3σ, or from a time when the 10-minute data acquisition rate was less than the threshold value. Here,the 10-minute data acquisition rate is the ratio of the number of valid data to the maximum number of data
during a 10-minute period. For the 10-minute data acquisition rate, in order to ensure that the wind speed,
wind direction and wind speed standard deviation are sufficiently accurate, set a threshold value withconsideration of the time intervals used in the switching between each measurement height.
Additional filtering may be performed as needed.
Calculate the effective data rate after the filtering. Describe the filtering performed in the report.
In addition to the above, other possible filtering methods given to remove abnormal values and unreliabledata include the use of the quantile value of the radial velocity, and the use of the difference between the
maximum value and the average over a 10-minute period10)-16).
The 3σ filter is the general method used in quality control to remove abnormal values. An instantaneous valueof radial velocity is excluded if it exceeds 3σ from the 10-minute average value or median value13).
In addition, it has been reported that high measurement accuracy can be achieved when the threshold value
for the 10-minute data acquisition rate is set to 10% or more (so that the number of valid data items for 1 secondof sampling must be 60 or more) and the time interval used in the switching between each measurement heightis set to 10 to 20 seconds13).

4.3.3 Calculation of horizontal wind speed and wind speed standard deviation
Calculate the horizontal wind speed and wind speed standard deviation from the radial velocity of eachSL.
The relationship between the radial velocity Vr and the horizontal components u, v and vertical component
w of the wind velocity can be expressed by the equation (4.1) using the azimuth angle 𝜙𝜙 and the elevation
angle 𝜃𝜃.

𝑉𝑉𝑉𝑉 = 𝑢𝑢 𝑠𝑠𝑠𝑠𝑠𝑠 𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃 + 𝑣𝑣 𝑐𝑐𝑐𝑐𝑐𝑐 𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃 + 𝑤𝑤 𝑠𝑠𝑠𝑠𝑠𝑠 𝜃𝜃(4.1)

Here, the definitions of the radial velocity, azimuth angle and elevation angle are shown in Figure 4.4. The
calculation of the horizontal components u, v of the wind velocity from the radial velocity of the two SL units
may be performed by omitting the third term on the right-hand side of equation (4.1) and using the following
equations (4.2) and (4.3)9).
𝑉𝑉𝑟𝑟 𝑐𝑐𝑐𝑐𝑐𝑐 𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃 −𝑉𝑉𝑟𝑟 𝑐𝑐𝑐𝑐𝑐𝑐 𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃

2
2
2
1
1
𝑢𝑢 = 𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃 1𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃 (𝑠𝑠𝑠𝑠𝑠𝑠
𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜙𝜙 −𝑠𝑠𝑠𝑠𝑠𝑠 𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜙𝜙 )
1

2

1

23

2

2

1

(4.2)

𝑉𝑉𝑟𝑟 𝑠𝑠𝑠𝑠𝑠𝑠 𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃 −𝑉𝑉𝑟𝑟 𝑠𝑠𝑠𝑠𝑠𝑠 𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃

1
1
1
2
2
𝑣𝑣 = 𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃 2𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃 (𝑠𝑠𝑠𝑠𝑠𝑠
𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜙𝜙 −𝑠𝑠𝑠𝑠𝑠𝑠 𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜙𝜙 )
1

2

1

2

2

1

(4.3)

Here, the subscripts indicate the outputs from the first and second scanning LiDAR units.

Figure 4.4 Relationship between the radial velocity and the horizontal and vertical components of the wind velocity

The calculation of the scalar wind speed U and the wind direction α from the horizontal component of thewind velocity can be performed using equations (4.4) and (4.5).
(4.4)

𝑈𝑈 = √𝑢𝑢2 + 𝑣𝑣 2𝑢𝑢
𝛼𝛼 = arctan � � + 𝛼𝛼0
𝑣𝑣

+180;
𝛼𝛼0 = �−180;

𝑢𝑢

𝑓𝑓𝑓𝑓𝑓𝑓 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 �𝑣𝑣 � < 180𝑢𝑢𝑓𝑓𝑓𝑓𝑓𝑓 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 �𝑣𝑣 � > 180(4.5)

The instantaneous values obtained for the scalar wind speed and the wind direction are used to calculate the
10-minute values of the average horizontal wind speed, the average horizontal wind direction, and the windspeed standard deviation. There is a risk that the length of the range gate may lead to an underestimation of thestandard deviation of the wind speed17),18). In this case, correction should be performed in accordance with 8.3.3.

24

5. Offshore measurement using Single Scanning LiDAR
5.1 Selection of measurement points
5.1.1 Selection of measurement points
Decide the measurement points based on the wind turbine layout and with consideration of therepresentative radius and the data acquisition rate at the offshore point.
The measurement point in SSL measurement is the center of the measurement azimuth sector.
Install the SL in a location where there are no obstacles such as structures and trees along the line of sight
between the installation location of the SL and the measurement point.
The measurement azimuth sector should be decided with consideration of the wind direction appearance
frequency distribution and the wind speed uniformity at the planned site.
For the measurement heights, in order to properly evaluate the wind shear on the wind turbine rotor plane,
perform measurements for a total of at least three heights.
It is desirable that the size of the measurement azimuth sector (the arc range to be scanned) be from 30° to
60°10).
The measurement error becomes large for wind that is blowing in the direction orthogonal to the laser
irradiation, so it is desirable to select an installation location where the direction of the laser irradiation will not
be orthogonal to the main wind direction. It is desirable to avoid a laser irradiation direction that is within ±15°of the direction orthogonal to the main wind direction.
In PPI measurement using SSL, in order to assume the uniformity of the wind speed within the measurement
azimuth sector, the installation site is selected so that the changes in the topography and surface roughness
within a sector are as small as possible.
The other recommendations are the same as in 4.1.1.

5.1.2 Installation of equipment
See 4.1.2.

5.1.3 Hard target adjustment
See 4.1.3.
Two or more hard targets are required in order to estimate the tilt angle and roll angle of the measurement
sector plane.
In PPI measurement using SSL, if the tilt angle and the roll angle of the measurement sector plane are known,
the azimuth with small inclination can be used for the measurement, and the height correction in the analysis
can be considered.

25

5.2 Measurement of wind speed and wind direction
See 4.2.
Set the size of the measurement azimuth sector and the scan speed so that the requirements for accuracy
and effective data rate are satisfied.
In measurement using SSL, it is possible to observe the wind speed and the wind direction by using the PPI
mode, in which the elevation angle is fixed and the azimuth angle is gradually varied.
Wherever possible, it is desirable that the same measurement conditions (measurement distance,measurement azimuth sector size, and wind speed distribution) be used for the measurements at the planned site
and the accuracy verification. In particular, there is a risk that the accuracy at the time of the verification will
not be guaranteed if there is a significant difference between the accuracy verification conditions and themeasurement distance or wind speed distribution (wind speed uniformity) at the planned site.
At present, there are cases in which just the standard measures on SL against snow accumulation and freezing(such as the wiper operation settings and wiper washer fluid concentration) do not have a sufficient effect, so it
is hoped that solutions will be found in the future. Conduct periodic monitoring and corrective action to ensurethat there are no long periods of missing measurement data in the winter.

5.3 Data analysis
5.3.1 Flow of data analysis
Perform the evaluation of the measurement results in accordance with the items related to wind speed andwind direction in Table 2.1.
Clearly indicate the procedure for calculating the 10-minute average horizontal wind speed and winddirection from the radial velocity obtained from the SL. Also include filtering in the procedure.
An example of the data analysis procedure is shown in Figure 5.1. When there is more than one filtering
process, clearly indicate them so that it is possible to know their order.

26

Figure 5.1 Example flowchart of data analysis procedure

5.3.2 Filtering
See 4.3.2. However, it is not necessary to use the item for the removal of data when the radial velocities
from the two units are not synchronized.
It has been reported that sufficient measurement accuracy can be achieved when the threshold value for the
10-minute data acquisition rate is set to 10% or more and the number of radial velocity data to be input toequation (5.5) is set to 4 or more22).

5.3.3 Calculation of horizontal wind speed
The horizontal wind speed is calculated from the radial velocity from the SL.

The calculation of the horizontal components u, v of the wind velocity from the radial velocity Vr may also
be performed using PPI22). As in the case of DSL measurement, the relationship between the radial velocity andthe horizontal components and vertical component of the wind velocity can be expressed using the azimuth
angle φ and the elevation angle θ. The calculation formulas include Velocity Volume Processing (VVP) and
Velocity Azimuth Processing (VAP)10). The example of VVP is shown here.

27

𝑉𝑉𝑉𝑉 = 𝑢𝑢 𝑠𝑠𝑠𝑠𝑠𝑠 𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃 + 𝑣𝑣 𝑐𝑐𝑐𝑐𝑐𝑐 𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃 + 𝑤𝑤 𝑠𝑠𝑠𝑠𝑠𝑠 𝜃𝜃(5.1)

𝑉𝑉𝑉𝑉 = 𝑢𝑢 𝑠𝑠𝑠𝑠𝑠𝑠 𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃 + 𝑣𝑣 𝑐𝑐𝑜𝑜𝑜𝑜 𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃(5.2)

Here, if the third term on the right-hand side is omitted, the equation (5.1) becomes:

The horizontal components u, v of the wind speed can be calculated using the least squares method from theplurality of sets of observed values of the radial velocity and the azimuth angle that are obtained from one PPI
scan. Specifically, if the sum of squares of the estimated error is:
1′
2
𝐽𝐽 = ∑𝑁𝑁
𝑖𝑖=1{𝑉𝑉𝑟𝑟 − (𝑢𝑢 𝑠𝑠𝑠𝑠𝑠𝑠 𝜙𝜙 + 𝑣𝑣 𝑐𝑐𝑐𝑐𝑐𝑐 𝜙𝜙)}
2

and

𝜕𝜕𝜕𝜕

𝜕𝜕𝜕𝜕

𝜕𝜕𝜕𝜕

= 0,

𝜕𝜕𝜕𝜕

(5.3)

(5.4)

=0

are given as conditions, then u and v become:∑ 𝑐𝑐𝑐𝑐𝑐𝑐 2 𝜙𝜙𝑢𝑢
1� �=∑ 2 ∑ 2
�𝑠𝑠𝑠𝑠𝑠𝑠 𝜙𝜙 𝑐𝑐𝑐𝑐𝑐𝑐 𝜙𝜙−(∑ 𝑐𝑐𝑐𝑐𝑐𝑐 𝜙𝜙⋅𝑠𝑠𝑠𝑠𝑠𝑠 𝜙𝜙)2 − ∑ 𝑐𝑐𝑐𝑐𝑐𝑐 𝜙𝜙 ⋅ 𝑠𝑠𝑠𝑠𝑠𝑠 𝜙𝜙𝑣𝑣− ∑ 𝑐𝑐𝑐𝑐𝑐𝑐 𝜙𝜙 ⋅ 𝑠𝑠𝑠𝑠𝑠𝑠 𝜙𝜙 ∑ 𝑠𝑠𝑠𝑠𝑠𝑠 𝜙𝜙 ⋅ 𝑉𝑉𝑟𝑟 ′���∑ 𝑠𝑠𝑠𝑠𝑠𝑠2 𝜙𝜙∑ 𝑐𝑐𝑐𝑐𝑐𝑐 𝜙𝜙 ⋅ 𝑉𝑉𝑟𝑟 ′(5.5)

Here, Vr′ is Vr/cos θ. As in the previous section, the calculation of the scalar wind speed U and the winddirection α from the horizontal component of the wind velocity is performed using equations (4.4) and (4.5).
The short-time average values obtained for the scalar wind speed and the wind direction (for example, theaverage over 15 seconds if it is a 45° horizontal scan performed at 3° per second) are used to calculate the 10minute values of the average horizontal wind speed and the average horizontal wind direction.

Figure 5.2 Relationship between the radial velocity and the horizontal and vertical components of the wind velocity

28

6. Offshore measurement using vertical LiDAR
6.1 Selection of measurement points
6.1.1 Selection of measurement points
Select the measurement points based on the wind turbine layout and with consideration of therepresentative radius. When simultaneous measurement will be performed with a meteorological mast, theinstallation should be in a location adjacent to the meteorological mast.
It is desirable that measurements by VL be performed in accordance with IEC 61400-12-1:2017 Annex L
The application of remote sensing technology. The laser must be installed so that it does not hit an obstacle.
The further the distance from the meteorological mast becomes, the lower the correlation becomes for thewind speeds and wind directions.

6.1.2 Installation of equipment
See 4.1.2.
It is desirable for the installation of VL to be performed in accordance with IEC 61400-12-1:2017 Annex L.
When VL is installed, azimuth determination is important in order to direct the north mark to the accurate
azimuth. If the north mark is installed in a direction other than north, measure the exact offset value. Also, when
installing equipment on a platform, perform adjustment so that the roll angle and tilt angle on the inclinometer
inside the equipment become less than ±0.2°, and confirm that these are being maintained during themeasurement period. The definitions of the tilt angle and roll angle are the same as in Figure 4.2. Fix theequipment to the platform firmly so that it does not shift during the measurement period.
It is desirable to install fences around the equipment and platform so that animals and people other thanrelated staff cannot enter.
If the planned site is an area where snow accumulates, set an appropriate platform height based on past
weather records.
When installing a vertical LiDAR on the platform of an offshore meteorological mast, evaluate the external
conditions at the site and take steps to prevent the equipment and power systems being directly hit by highwaves or breaking waves. Wind measurements at sea are more likely to be affected by salt damage, wave
splashing, and sand scattering than those on land, so higher weather resistance is required. Measurement
sensors, cables, loggers, and power supply systems (including fuel cells) must have adequate measures
implemented for waterproofing, dustproofing, and protection against salt damage (such as shielding, painting,and insulation strengthening), and it is desirable to prepare so that a rapid response can be made in the eventof a failure.
For the power supply system, assume that access difficulties will occur due to stormy weather, andappropriately implement suitable redundancy measures and emergency response measures.

29

6.2 Measurement of wind speed and wind direction
Conduct wind speed and wind direction measurement with devices that have had their accuracy verified
in advance. Perform the pre-deployment verification of accuracy for VL in accordance with the procedure in
IEC61400-12-1:2017, or in a procedure recognized as equivalent, and attach the verification results to thereport. After the end of the measurement period, confirm that the measurement accuracy has been maintained.
For the measurement height, in order to evaluate the wind shear at the wind turbine rotor plane, set multiple
measurement heights that include three points near the hub height, the rotor top tip height, and the rotor
bottom tip height.
For the wind speed, measure the 10-minute mean value.
Also, in cold regions where the temperature of the planned site falls below zero, implement measuresagainst snow accumulation and freezing.
For VL, the measurement height is set with consideration of the measurement height of the meteorologicalmast and the hub height and rotor diameter of the planned wind turbine.
When VL and a meteorological mast are combined to handle the data as measurement data at the hub height
and use it as input data for airflow analysis for the calculation of the site wind conditions, it is necessary tosatisfy requirements for the effective data rate after complementation that are equivalent to those for cup
anemometers and wind vanes.
Also, in cold regions where the temperature of the planned site falls below zero, measures must be taken
against freezing, such as the installation of heaters, the installation of wiper blades for winter, the setting ofappropriate wiper operation, and the adjustment of the concentration of wiper washer fluid.
Measurement errors occur in the measurement of turbulence intensity by VL, so it is necessary to correct thisby the method proposed by Yamaguchi et al2).

6.3 Data analysis
Perform the evaluation of the measurement results in accordance with the items related to wind speed andwind direction in Table 2.1.
Before performing analysis, perform filtering to remove any abnormal values and calculate the effective
data rate. Indicate the data removal method and criteria applied at the time of the calculation in the report.
Example methods for calculating the horizontal wind speed from the radial velocity of VL are the DBS
method and the VAD method. The equation shown here is the equation for calculating the horizontal wind speed
components u, v from the radial velocity in the north, south, east, and west directions by the DBS method. In
addition, the equation for calculating the vertical wind velocity component w is also shown. The definitions ofradial velocity and elevation angle are given in Figure 6.1.

𝑢𝑢 =𝑢𝑢𝑟𝑟𝑟𝑟 −𝑢𝑢𝑟𝑟𝑟𝑟

(6.1)

𝑢𝑢

(6.2)

2 𝑠𝑠𝑠𝑠𝑠𝑠 𝜃𝜃−𝑢𝑢𝑣𝑣 = 2𝑟𝑟𝑟𝑟𝑠𝑠𝑠𝑠𝑠𝑠 𝜃𝜃𝑟𝑟𝑟𝑟

30

𝑤𝑤 =

𝑢𝑢𝑟𝑟𝑟𝑟 +𝑢𝑢𝑟𝑟𝑟𝑟 +𝑢𝑢𝑟𝑟𝑟𝑟 +𝑢𝑢𝑟𝑟𝑟𝑟(6.3)

4 𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃

or,

(6.4)

𝑤𝑤 = 𝑢𝑢𝑟𝑟𝑟𝑟

Where:

𝑢𝑢𝑟𝑟𝑟𝑟 : radial velocity in northerly direction, 𝑢𝑢𝑟𝑟𝑟𝑟 : radial velocity in southerly direction, 𝑢𝑢𝑟𝑟𝑟𝑟 : radial velocity
in easterly direction, 𝑢𝑢𝑟𝑟𝑟𝑟 : radial velocity in westerly direction, 𝑢𝑢𝑟𝑟𝑟𝑟 : radial velocity in vertical direction,𝜃𝜃: elevation angle

Figure 6.1 Definitions of radial velocity and elevation angle31

7. Offshore measurement using a Floating LiDAR System
7.1 Selection of measurement points
7.1.1 Selection of measurement points
Select the measurement points based on the wind turbine layout and with consideration of the representative
radius. When simultaneous measurement will be performed with an offshore meteorological mast, theinstallation should be in a location adjacent to the offshore meteorological mast. In addition to the naturalenvironmental conditions, sufficient consideration should also be given to social environmental conditions
such as the volume of vessel traffic, fishing areas, and seabed obstacles.
It is desirable that the selection and installation of FLS measurement points be conducted in accordance withIEA RP 18. Floating LIDAR systems (2017) and Carbon Trust OWA Roadmap for the Commercial Acceptanceof Floating LiDAR Technology (2018) (hereinafter referred to as the “Carbon Trust OWA Roadmap for FLS”).
In the selection of an FLS, gain a sufficient understanding of the natural environmental conditions at the
installation site, such as the weather and sea conditions, water depth, and distance from the shore, and thenselect a model suitable for the investigation purpose and the application.
When simultaneous measurement is performed with an offshore meteorological mast, the further the distance
between the FLS and the offshore meteorological mast becomes, the lower the correlation becomes for the windspeed and the wind direction, so the FLS and the offshore meteorological mast should be placed as close together
as possible. When performing FLS accuracy verification or calibration, it is desirable that the distance between
the FLS and the offshore meteorological mast be within 500 m. In the same way, a distance of within 500 m isalso desirable when an FLS and an offshore meteorological mast are combined to handle the data asmeasurement data at the hub height and use it as input data for airflow analysis for the calculation of the site
wind conditions. It is desirable that the distance between the FLS and the offshore meteorological mast be within
the recommended distance described above, but the distance should be set according to the situation of the sitemeasurement such as the local water depth and the mooring system of the FLS.
In FLS measurement, once the measurements have begun at sea, the aspect of access means that it is not easy
to carry out maintenance work at the site. For this reason, it is necessary to carefully perform accuracy
verification and operation checks for each system to be used on the FLS before installing the FLS in the site sea
area.
Figure 7.1 shows an example FLS layout for reference.

32

Figure 7.1 Example FLS layout

7.1.2 Installation of equipment
When installing an FLS, it is necessary to conduct the prescribed authorization procedures with the Japan
Coast Guard and the relevant prefectural departments. In addition, before installing the equipment, perform
sufficient coordination with the users of the sea area, such as those involved in fisheries, harbors, andmaritime affairs, and also widely publicize information on the specifications and schedule of themeasurements.
The installation work involves various related parties such as the requesting party, the manufacturer, andthe contractor conducting the installation work, so it is important to clarify the division of work and thesystem of instructions at the stage of the execution planning, and to incorporate these into the execution plan,
including the safety management aspects.
Constantly monitor the position information for the FLS during the measurement period and put in place
an emergency system to immediately respond to any problems such as mooring failure.
An accident of FLS mooring failure could have far-reaching effects in Japan’s coastal waters. In particular,
it is necessary to avoid causing damage to other users of the sea area, and this resulting in an impact on theentire power generation business. The following points are important in order to prevent mooring failure
accidents, and to minimize the impact if such an accident occurs.
• Gaining an understanding of the sea conditions and weather conditions in the installation sea area
• Implementing a detailed mooring analysis and careful design checks to ensure a high safety factor• Improving the efficiency of the work on site during the execution and avoiding human error based on achecklist• Constant monitoring of the FLS position and the construction of an alert communication system in case ofmooring failure• Preparation of a crisis management manual and an emergency contact network and a prompt initial33

response in the event of a mooring failure• Investigation of the impacts of mooring failure and responses for the relevant parties• Resumption of measurement based on careful investigation of the cause of a mooring failure andconsideration of recurrence prevention measures
Figure 7.2 shows an example of the flow of FLS installation work for reference.

Figure 7.2 Example flow of FLS installation work

Installation and maintenance work at sea often involve periods having to wait on standby due to stormy
weather. In FLS measurements, it is desirable to carry out process control with the top priority given to safety
and a reasonable schedule for matters such as authorization procedures and the arrangement of various work.
Examples of FLS installation work are shown in Annex D.
Table 7.1 shows an example of the flow of authorization procedures for FLS for reference. At present, there
are few previous examples of FLS installation, so there are concerns that the procedures may not advancesmoothly. It is important to gain an understanding of the local issues through prior consultation.

34

Table 7.1 Example of the flow of authorization procedures for FLS installation
No.
1

Item
Preparation

Counterparty-

Contents

Main related laws
and regulations

Preparation of FLS installation plan,
information survey using NeoWins, etc.*1,
understanding of contents of eachguidebook, understanding of sea area of
installation*22

Prior consultation

Prefecture

Explanation of FLS installation plan,check of utilization procedures,

Coast Guard Officeunderstanding the fishery personnel andsea area users

Fisheries

Explanation of FLS installation plan,

cooperative

consultation on facility lights,

Fishery Act

understanding the fishery personnel andsea area users
Greetings and explanations to fisheryrepresentatives from fishery cooperatives,
etc., understanding the situation of thelocal fishing industry and the sea areas
where fishery rights are applicable3

Application for

Coast Guard Office

Application for installation of permission

Navigation Aid

signs and simplified signs, etc.

Act

Permission to use a sea area by installing

Prefecturalpermission to occupy aa floating body and mooring lines and theordinances andsea areapayment of costs

controlpermission to installnavigational aids*3
4Application forPrefecture*4

regulations
5

Dissemination ofFishery personnel

Preparation and distribution of materials

information to related

Water area users

to disseminate information on the FLS

parties6

installation plan

Application for

Coast Guard OfficePermission application or notification

Port Regulations

construction work

(Station)submission for maritime construction,

Act or Maritime

work, etc.

Traffic Safety Act

Use of port facilities such as quays andPort and Harbor

yards

Act

permission*5
7Application for port
facility use

Port administrator*1. Use resources such as NeoWins (the NEDO Offshore Wind Conditions Map) to investigate the social and environmental
information for the target sea area in advance (such as the fishery rights, port area, fishing port area, passage, QuasiNational Parks, etc.).
*2. The sea areas where FLS are installed are mainly divided into two types: port areas and general sea areas. General sea
areas are areas of the territorial sea and inland water that are not a port area or any other area provided for in a relevantlaw.
*3. A lot of FLS products come from overseas, so the Coast Guard Office procedures for lighting may take some time. It is
desirable to make the application with sufficient time. Also, confirm that the communication equipment complies with
the Radio Act (the Ministry of Internal Affairs and Communications).
*4. The ordinances and control regulations, etc., enacted by individual prefectures are applied to the permission to occupy
general sea areas. Caution is required as the contact point responsible differs from prefecture to prefecture.
*5. The period required for the procedures for No. 3 to No. 6 is about two to three months.

35

The method for determining the water area occupied depends on the mooring method. The case of the Aomori
Prefecture Kamikita District Administration Office is shown below.
Table 7.2 Example methods of occupied area calculation
Mooring typeContents

Single point catenary mooring buoy

Drifting radius squared x 3.14

Three point catenary mooring buoys

Main body: Drifting radius squared x 3.14
Mooring lines: Width x Length x Quantity
Anchors: Length x Width x Quantity[Example methods of occupied area calculation]
Drifting radius:

102 mOccupied area:

102 m × 102 m × π ＝ 32,669 m2(a) Single point catenary mooring buoy

[Example methods of occupied area calculation]
Drifting radius: 20 m
Occupied area:(Main body) 20 m × 20 m × π ＝ 1,256 m2(Mooring lines) 0.2 m × 320 m × 3 ropes ＝ 1,536 m2(Anchors) 5 m x 1.5 m x 3 places = 24 m2
Total 2,816 m2(b) Three point catenary mooring buoy
Figure 7.3 Example methods of occupied area calculation

36

7.2 Measurement methods
See 6.2.
An FLS is an measurement system in which an measurement part including VL and a floating body platform
are integrated. Therefore, the wind condition measurement method using an FLS is the same as themeasurement method using VL.
Although the Carbon Trust OWA Roadmap for FLS has established a methodology for evaluating thetechnical maturity of FLS equipment, there are still not many systems that have achieved Stage 3, which is thehighest technical maturity.
The turbulence intensity obtained from an FLS tends to be excessive due to the swaying motion of thefloating body. In order to remove this effect, there are FLS that have a function to compensate for the swaying
motion, and methods for correction by post-processing the measurement data3),4). Correction is necessary inthe same way as for the VL described above2).

7.3 Data analysis methods
Perform the evaluation of the measurement results in accordance with the items related to wind speed andwind direction in Table 2.1.
Before performing analysis, perform filtering to remove any abnormal values and calculate the effective
data rate. Indicate the data removal method and criteria applied at the time of the calculation in the report.

37

8. Complementation of missing data and its accuracy verification
8.1 System utilization rate and effective data rate
The system utilization rate ξ [%] during the measurement period is the number of 10-minute data sets when
the system was operating divided by the total number of 10-minute periods during the measurement period,and is defined by equation (8.1).
𝜉𝜉 =Number of 10-minute periods the system
Total number of 10-minute periods during the measurement period

× 100 (%)

(8.1)

The effective data rate during the measurement period after filtering η [%] is the number of 10-minute data
sets after applying the aforementioned filter for removing abnormal values from the acquired data, divided
by the total number of 10-minute periods during the measurement period, and is defined by equation (8.2).
𝜂𝜂 =Number of 10-minute periods which data is valid
Total number of 10-minute periods during the measurement period

× 100 (%)

(8.2)

The abnormal values are removed from the measurement data before they are evaluated as the windconditions necessary for the prediction of the energy yield and for the wind turbine design. As described in 2.3,
it is necessary to have an effective data rate of 95% or more after the filtering to remove abnormal values. Whenthe effective data rate does not satisfy 95%, complementation is performed using nearby measurement data.
Compared to meteorological masts, RSD are more affected by weather conditions and tend to have a lower
effective data rate, so there is a high necessity for complementation. For the measurement data used for thecomplementation, it is recommended to use the measurement data from meteorological masts and vertical
LiDAR installed on the land in the vicinity of the offshore measurement point. See Chapters 3 and 6,
respectively, for the requirements for the meteorological masts and VLs. However, the matters concerning
offshore measurement are unnecessary.

8.2 Complementation of missing data
If there is a period in which the wind condition measurement data is missing or shows abnormal values,
such as due to a failure of the measurement devices or weather conditions, etc., and the effective data rate
does not satisfy 95%, perform compensation using nearby measurement data. The effective data rate after thecomplementation should be at least 95%. If compensation using measurement data is performed, verify theaccuracy of that complementation and show the validity of the complemented data.
It is desirable that there are no particular periods during the year when the wind condition measurement datais missing or is abnormal values.
For reference, Table 8.1 shows the Key Performance Indicators (hereinafter referred to as KPI) andacceptance criteria in the Carbon Trust OWA Roadmap for FLS for the effective data rate after filtering. ThisKPI here means the key performance indicators for evaluating the RSD system utilization rate, effective data
38

rate, and accuracy.
When evaluating the wind conditions over the year, the recommended value for the monthly effective data
rate should be set with reference to Table 8.1.
Table 8.1 KPIs and acceptance criteria for the effective data rate for FLS after filtering
KPI

Acceptance criteria

Monthly effective data

Stage 2: ≥ 80%

rate after filtering

Stage 3: ≥ 85%

Annual effective data

Stage 2: ≥ 85%

rate after filtering

Stage 3: ≥ 90%

If the annual effective data rate does not satisfy 95%, perform complementation using measurement data frommeteorological masts and VL installed in the vicinity of the measurement point.
The complementation of the wind speed and wind direction is generally performed using the MeasureCorrelate-Predict (hereinafter referred to as “MCP”) method. The MCP method is a method in which the missing
data of the complementing target is predicted from the data of the complementing source by using a linear
regression equation that is calculated using the data of the complementing source and the data of thecomplementing target when those data exist for the same points in time.
For the correction of the standard deviation of wind speed, as the error of the 90% quantile value of turbulence
intensity by the linear regression equation is large, Watanabe14) et al. proposed a method using double bias
correction (DBC)26).

39

8.3 Accuracy KPIs and acceptance criteria
8.3.1 Wind speed and wind direction

Table 8.2 shows the KPIs and acceptance criteria for wind speed and wind direction accuracy in all winddirections. For wind speed, the KPIs are the regression equation slope and coefficient of determination bycorrelation analysis. For wind direction, the KPIs are the regression equation slope, intercept, and coefficientof determination. The intercept of the regression equation for the wind direction is the difference between the
average value of the reference wind direction and the LiDAR wind direction average.
Table 8.2 Accuracy KPIs and acceptance criteria
KPI

Evaluated item

Slope of theWind speeds of 4 m/s or more andMinimum: 0.97 to 1.03

Wind

regression equation

less than 16 m/s

Best practice: 0.98 to 1.02

speed

Coefficient ofdetermination

Accuracy acceptance criteria

Minimum: ≥ 0.97

As above

Best practice: ≥ 0.98

Slope of theWind speeds of 4 m/s or more andMinimum: 0.95 to 1.05

regression equation

less than 16 m/s

Best practice: 0.97 to 1.03

Wind

Intercept of thedirection

regression equation
Coefficient ofdetermination

Minimum: < 10°

As above

Best practice: < 5°
Minimum: ≥ 0.95

As above

Best practice: ≥ 0.97

If data complementation is used, check whether the complementation method is appropriate. Evaluate thecomplemented measurement data by using accuracy KPIs and acceptance criteria.
Accuracy verification methods that take into account the effective data rate of the measurement data
include the research by Enoki and Ishihara25) and the research by Watanabe et al.14).
The wind speed range when performing accuracy verification should be 4 m/s or more and less than 16 m/s.
For reference, Table 8.3 shows the wind speed range for accuracy verification in the Carbon Trust OWA
Roadmap for FLS. In the Carbon Trust OWA Roadmap for FLS, the purpose is to evaluate the performance of
the FLS as a device, so evaluation at 2 m/s or higher is included. In the IEC61400-50-2 classification tests, therange is 4 m/s or more and less than 16 m/s. As described in Chapter 2, the purpose in this Guidebook is thewind condition estimation necessary for the prediction of the energy yield and the wind turbine design, so therange covered is 4 m/s or more and less than 16 m/s, which is the wind speed range that contributes greatly topower generation and load.

40

Table 8.3 Accuracy KPIs and acceptance criteria in the Carbon Trust OWA Roadmap for FLS
KPI
Slope of the regression
Wind
speed

equation
Coefficient ofdetermination
Slope of the regression
equation

Wind

Intercept of thedirection

regression equation
Coefficient ofdetermination

Evaluated itema) Wind speeds of 4 m/s or more
and less than 16 m/sb) 2 m/s or more

Accuracy acceptance criteria
Minimum: 0.97 to 1.03
Best practice: 0.98 to 1.02
Minimum: ≥ 0.97

As above

Best practice: ≥ 0.98
Minimum: 0.95 to 1.05

2 m/s or moreBest practice: 0.97 to 1.03
Minimum: < 10°

As above

Best practice: < 5°
Minimum: ≥ 0.95

As above

Best practice: ≥ 0.97

8.3.2 Wind speed standard deviation
In the accuracy verification for turbulence intensity, perform evaluation based on the following indices andalso present charts comparing the RSD with a cup anemometer regarding the wind speed standard deviation
per wind speed class (mean value and 90% quantile value) and the frequency distribution by wind speed
class.
The range for the evaluation should be the wind speed data that is 4 m/s or more and less than 16 m/s.
90% quantile of standard deviation of wind speed for kth bin (𝜎𝜎90𝑘𝑘 )= 𝜎𝜎𝑘𝑘 + 1.28 ⋅ 𝑠𝑠𝑠𝑠𝑠𝑠(𝜎𝜎𝑘𝑘 )Bin weighted average error (-)= ∑𝑁𝑁
𝑘𝑘=1 𝑓𝑓𝑘𝑘 ⋅ �𝜎𝜎90𝑅𝑅𝑅𝑅𝑅𝑅,𝑘𝑘 − 𝜎𝜎90𝑐𝑐𝑐𝑐𝑐𝑐,𝑘𝑘 �

(7.3)
(7.4)

Where:

𝑁𝑁: Number of wind speed bins (k = 1, 2, ..., N)

𝜎𝜎90𝑅𝑅𝑅𝑅𝑅𝑅,𝑘𝑘 : 90% quantile of the standard deviation of the wind speed of the kth bin of the LiDAR

𝜎𝜎90𝑐𝑐𝑐𝑐𝑐𝑐,𝑘𝑘 : 90% quantile of the standard deviation of the wind speed of the kth bin of the cup anemometer
𝑓𝑓𝑘𝑘 : Frequency ratio of the kth bin of the cup anemometer𝜎𝜎𝑘𝑘 : Average value of standard deviation of wind speed for kth bin

𝑠𝑠𝑠𝑠𝑠𝑠(𝜎𝜎𝑘𝑘 ): Standard deviation of standard deviation of wind speed for kth bin
In addition to a chart comparing the standard deviations of the wind speeds, it is desirable to also show achart comparing the turbulence intensities.

41

8.3.3 Correction of wind speed standard deviation
If the result of the verification of the turbulence intensity accuracy is that it is an underestimate, correction
must be performed. If a correction is made, repeat the verification of the accuracy to show the validity of thecorrected data.
The possible correction methods when the DSL turbulence intensity is an underestimate include to add thedifference between the standard deviations of the wind speeds of the DSL and cup anemometer by wind speed
class17),18). Caution is required if the measurement height at the time of the accuracy verification differs fromthe measurement height at the offshore measurement point at the planned site, because the error may differ
depending on the height.
After a correction, in addition to a chart comparing the standard deviations of the wind speeds, it is desirable
to also show a chart comparing the turbulence intensities.

42

9. Reporting
9.1 Installation and measurement reports
Reports of the measurements at a site and reports of the evaluation of measurement results should comply
with IEC61400-12-1 and indicate at least the following items.
(1) Site situation


Exact coordinates of the measurement points (including datum)Photographs taken in a 360° circumference around all the measurement points



Topographic map of the site showing the measurement points(2) Description of the measurement systemSpecifications of the measurement devices and data collection systems (including calibration reportfor the measurement devices and RSD verification results)

The installation, layout and setting heights of the measurement apparatus (all the sensors and
RSDs)



If a scanning LiDAR is used, a document showing the accuracy of the measurement

Measurement device layout diagram and drawings including the main dimensions



Document indicating that the accuracy of the wind speed measurement during the measurement
period was maintained(3) Description of the measurement procedureDescription of the measurement procedure, sampling frequency, averaging time, measurement
period

Records (dates and times) of all significant events and maintenance during the measurement period

With respect to the install and layout of the instruments, indicate the height level such as the ground level
and/or the mean sea level. If an RSD is to be mounted on a platform, the height of the platform should also be
indicated, and the height set for the device and the height above the ground should be indicated.
The RSD validation results referred to here are the results of the pre-shipping testing by the manufacturer. If
no RSD verification results are provided by the manufacturer, this should be indicated. Section 8.3 describes
the report of RSD verification at a site.
It is desirable to indicate the measurement point, the planned wind turbine position, and the separation
distance.

43

9.2 Evaluation report
At least the following items should be included in the evaluation of the measurements.
(1) Effective data rate
Include the effective data rate for the entire measurement period and for each month. Include thedata removal criteria applied when calculating the effective data rate.
(2) Wind direction and wind speed
Include the average value, minimum value and maximum value of the wind speed in tabular form

for the entire measurement period and for each month.
Include the Weibull shape coefficients and scale coefficients by directional and the frequency

distribution by directional in a tabular form (with wind direction sectors that do not exceed 30°).
Include a wind rose.
(3) Turbulence intensity
Include the ambient turbulence intensity by directional in a tabular form (with wind direction

sectors that do not exceed 30°).
Include a comparison of the ambient turbulence intensity with the IEC Turbulence Category(NTM), considering all directions.
The number of measurement heights included in the evaluation report should be at least three heights forwind speed and one height for turbulence intensity.

9.3 Verification report
When an RSD is used, show the results of checks of the requirements for accuracy verification shown in
Chapter 7.
(1) Measurement device installation report for the verification siteFollow section 8.1.

(2) Evaluation report for the measurement data used in the verification


Follow section 8.2.

(3) Verification resultsInclude the results of wind speed and wind direction correlation analysis (parameters and scatterplots) and the results of checks of the requirements.

Include the results of ambient turbulence intensity comparisons (parameters and figures) and theresults of checks of the requirements.

44

References
1)

T Mikkelsen, J Mann and M Courtney: Wind Scanner: A full-scale Laser Facility for Wind andTurbulence Measurements around large Wind Turbines, EWEC2008.

2)

Atsushi Yamaguchi, Akifumi Kyomasu, Takeshi Ishihara: Turbulence Measurement by Using Doppler
Lidar and its verification by using synthetic turbulent wind field, 44th Wind Energy Symposium, 2022.

3)

A.Yamaguchi, T.Ishihara: A new motion compensation algorithm of floating lidar system for theassessment of turbulence intensity, Journal of Physics: Conference Series 753 072034, 2016.

4)

F.Kelberlau, V.Neshaug, L.Lønseth, T.Bracchi, J.Mann: Taking the Motion out of Floating LIDAR:
Turbulence Intensity Estimates with a Continuous-Wave Wind LiDAR, Remote Sens. 12, 898, 2020.

5)

J.Eecen, L.A.H.Machielse, A.P.W.M. Curvers: Meteo- rological Measurements OWEZ Half year report,
01-07-2005-31-12-2005, 2007.

6)

D. Kindler and A. Gütschow: The FINO3 Wind Energy Research Platform in the North Sea: First
Results & Comparison to Concurrent FINO1 Data, Bremen, 2010.

7)

Koji Hayashida, Toru Yamanaka, Kazumasa Okubo, Takeshi Ishihara, Atsushi Yamaguchi, Yukinari
Fukumoto: The Wind Measurement for Offshore Wind Power Generation - Off the Coast of Choshi,
Journal of Wind Engineering, Vol. 43, No. 3, 2018.

8)

Leosphere M. Steger: Dual Scanning Lidar: Main Uncertainty Contributors, VAISALA webinar "Dualscanning lidar to increase accuracy and efficiency for offshore wind campaigns", 2021.

9)N. Vasiljevic, M. Courtney, A. Tegtmeier Pedersen: Uncertainty model for dual-Doppler retrievals ofwind speed and wind direction. Atmos. Meas. Tech. Discuss., 2020.

10) E. Simon, M. Courtney: A Comparison of sector-scan and dual Doppler wind measurements at Høvsøre
Test Station – one lidar or two? DTU Wind Energy. DTU Wind Energy E, Vol. 0112, 2016.
11) Susumu Shimada, Teruo Ohsawa, Ren Nakasato, Satoshi Nakamura, Yuko Takeyama, Tetsuya Kogaki,
Masaki Furukawa: Investigation on wind resource assessment methods at a potential offshore wind farmsite Part 1: Dual scanning LiDAR measurements, 40th Wind Energy Symposium, 2018.
12) Susumu Shimada, Tetsuya Kogaki, Mizuki Konagaya, Toshinari Mito, Takeshi Misaki, Ryuzo Araki,
Yuko Ueda, Teruo Ohsawa: The Mutsu-Ogawara Scanning LiDAR experiment Part 2: Dual scanning
LiDAR system validation, 43rd Wind Energy Symposium, 2021.
13) Keiichiro Watanabe, Susumu Takakuwa, Chikara Hemmi, Takeshi Ishihara: A study of offshore windassessment using dual-Doppler scanning lidars, Journal of Wind Energy, JWEA, Vol. 45, No. 2, pp. 4048, 2021.
14) Keiichiro Watanabe, Susumu Takakuwa, Chikara Hemmi, Takeshi Ishihara: Offshore wind assessment
using dual scanning lidar and missing data complement using MCP method, 43rd Wind Energy
Symposium, 2021.
15) Shizuka Ohhata, Ryuzo Araki, Susumu Shimada, Mizuki Konagaya, Teruo Ohsawa, Tetsuya Kogaki,
Yuko Ueda: Mutsu-Ogawara scanning lidar field experiments Part 4. Measurement parameters andaccuracy assessment in the dual-Doppler Lidar scanning mode, 43rd Wind Energy Symposium, 2021.
16) Gryning S.-E., and Floors R.: Carrier-to-Noise-Threshold Filtering on Off-Shore Wind Lidar
Measurements. Sensors.19(3):592. DOI: 10.3390/s19030592, 2019.
4517) Wataru Sasaki, Yukinari Fukumoto, Kaito Inomata, Michio Nittouji, Takeshi Ishihara: Validation of
Dual-Doppler LiDAR wind assessment using the met-mast at Choshi offshore site, 44th Wind Energy
Symposium, 2022.
18) Jun Tanemoto, Tsenwei Lin, Kazuya Takahashi, Koji Sumida, Tetsuji Shiroeda: Study on the correctionof turbulence intensity values observed by dual scanning LiDAR, 44th Wind Energy Symposium, 2022.
19) Jay Prakash Goit, Atsushi Yamaguchi, Takeshi Ishihara: Performance Evaluation of Scanning Doppler
Lidar and its Application to Wind Field Measurement, Journal of Wind Energy, JWEA, Vol. 42, No. 1,
pp. 7-16, 2018.
20) Ryuzo ARAKI: Comparative measurements of wind between scanning Doppler LiDAR andmeteorological mast on the west coast of Awaji Island, Journal of Wind Energy, JWEA, Vol. 43, No. 2,2019.
21) Akiko Mano, Akiyo Ueno, Shunsuke Itozaki, Takeshi Ishihara: Accuracy verification of 3D scanning
LIDAR and application to offshore wind measurement, 41st Wind Energy Symposium, 2019.
22) Akiko Mano, Akiyo Ueno, Shunsuke Itozaki, Takeshi Ishihara: Effects of data availability and sector
size on the accuracy of 3D scanning LiDAR measurements, 42nd Wind Energy Symposium, 2020.
23) S. Shimada, J. P. Goit, T. Ohsawa, T. Kogaki, S. Nakamura: Coastal wind measurements using a single
scanning LiDAR, Remote Sensing, 12, 1345, pp.1-24, 2020.
24) J.P. Goit, A. Yamaguchi, T. Ishihara: Measurement and Prediction of Wind Fields at an Offshore Site by
Scanning Doppler LiDAR and WRF, Atmosphere, 11, 442, pp.1-20, 2020.
25) Kota Enoki, Takeshi Ishihara: Formulas for evaluation of coefficient of determination, slope and offset
of wind speed and direction compensated by MCP method considering data availability of onsite
measurement, 43rd Wind Energy Symposium, 2021.
26) Mattias Lange, Ulrich Focken, Takeshi Ishihara, Atsushi Yamaguchi, Kenji Shimada, joint translation:“Physical Approach to Short-Term Wind Power Prediction - Toward a Stable Supply of Power”,
Ohmsha, 2012.
27) S. Shimada, T. Kogaki, M. Konagaya, T. Mito, R. Araki, Y. Ueda, T. Ohsawa: Validation of near-shore
wind measurements using a dual scanning light detection and ranging system, Wind Energy, Vol25,
pp1555-1572, 2022.

46

Annex A. Hard target adjustment

A.1
Cases when a hard target exists near an offshore measurement point
Figure A.1 shows the procedure for hard target adjustment in cases when a hard target exists in the vicinityof an offshore measurement point. When installing SL, perform adjustment so that the tilt angle and roll angle
on the inclinometer inside the equipment become less than ±0.02°, to satisfy the survey accuracy.

Figure A.1 Example of offshore hard target adjustment

47

A.2
In case of three hard targets
Figure A.2 shows the procedure for hard target adjustment in cases when there are three hard targets. It is
desirable to have an angle of about 120° between the hard targets. When installing SL, perform adjustment sothat the tilt angle and roll angle on the inclinometer inside the equipment become less than ±0.02°, to satisfy
the survey accuracy.

Figure A.2 In case of three hard targets

48

Figure A.2 In case of three hard targets (continued)

49

A.3
In case of two or fewer hard targets
Figure A.3 shows the procedure for hard target adjustment in cases when there are two or fewer hard targets.
When installing SL, perform adjustment so that the tilt angle and roll angle on the inclinometer inside theequipment become less than ±0.02°, to satisfy the survey accuracy.

Figure A.3 In case of two or fewer hard targets

50

Figure A.3 In case of two or fewer hard targets (continued)

51

Annex B. Pre-deployment verification of accuracy
B.1

Pre-deployment verification of accuracy
The pre-deployment verification of accuracy for DSL and SSL is performed based on regression analysis

using the measurement data from meteorological mast cup anemometers and wind vanes installed inaccordance with the requirements described in Chapter 3. The results of the correlation analysis of windspeed and wind direction are shown in a scatter plot.
Remove the abnormal values, flow distortion due to topography, and the effects of structures to performthe verification using the reliable data.
For the number of data required for the pre-deployment verification of accuracy, the number of dataremaining after the filtering in which the abnormal values and others are removed must satisfy theacceptance criteria shown in Table B.1.
Table B.1 Number of data required for accuracy verification
Evaluated item

Wind speed bin width

Acceptance criteria for number of data

2 m/s - 12 m/s

1 m/s

≥ 40

12 m/s - 16 m/s

2 m/s

≥ 40

> 16 m/s (if use possible)

2 m/s

≥ 40

The accuracy verification period should be set with consideration of the fact that the number of data will be
reduced by the weather conditions during the accuracy verification period and the filtering.

B.2

Accuracy KPIs and acceptance criteria

B.2.1

Wind speed and wind direction

See 8.3.1.
If the error in the wind speed or wind direction measured by the RSD is less than or equal to the minimum inTable 8.2, the measured value can be used as having an accuracy equivalent to that of a cup anemometer or awind vane.

B.2.2

Wind speed standard deviation

See 8.3.2.
If the error in the standard deviation of the wind speed measured by the RSD is 5% or less, the measured
value can be used as having an accuracy equivalent to that of a cup anemometer. For DSL, accuracy below thiserror has been reported in previous studies12) and was also confirmed in this project.

52

Annex C. Data acquisition rate check
C.3

Data acquisition rate check

Prior to conducting site measurements, conduct preliminary verification at the offshore measurement
points to ensure that sufficient data acquisition rates can be obtained. When checking the data acquisition
rate, the same settings as in the accuracy verification should be used.
The data acquisition rate at the measurement point is affected by the SL device performance (laser output,etc.), the measurement distance, the measurement settings (range gate, accumulation time, time intervals usedin the switching between each measurement height, focus), and the weather conditions (dense fog, heavy snow,
snowstorms, heavy rain, etc.).
It is not easy to change the measurement settings after starting site measurements, so it is desirable to checkthe data acquisition rate beforehand and formulate a careful measurement plan so that a sufficient dataacquisition rate can be obtained throughout the year.
It is desirable that a data acquisition rate of 60% or more is obtained during the period of the preliminary
verification for the measurement distance of the offshore measurement point where year-long measurement will
be carried out. It should be noted that as weather conditions vary throughout the year, it is not guaranteed thatthe data acquisition rates identified here will be representative values for a year at the planned point.

53

Annex D. Example FLS installation work
Figures D.1 to D.3 show the flow of installation work and mooring diagrams for three models as examplesof the installation work for each FLS.

(a) Flow of installation work
Figure D.1 SeaWatch installation case example and mooring diagram

54

(b) Mooring diagram(c) Floating body dimensions
Item

Contents

Type

Disk shaped

Dimensions

Diameter 2.8 m, total height 7.2 m

Draft

4m

WeightApprox. 2.2 tons(d) Mooring specifications
Item

Contents

Type

Single point mooring

Dimensions

Total length: 85.4 m(Upper chain 10 m + Rubber cord 35 m + Intermediate
float + Synthetic fiber rope 35 m + Bottom chain 4 m)

Sinker

3.3-ton chain

Figure D.1 SeaWatch installation case example and mooring diagram (continued)

55

(a) Flow of installation work

Figure D.2 WindSentinel installation case example and mooring diagram

56

(b) Mooring diagram(c) Floating body dimensions
Item

Contents

Type

Boat shaped

Dimensions

Length 6 m x Width 3.1 m x Height 9 m

Draft

4m

WeightApprox. 9 tons(d) Mooring specifications
Item

Contents

Type

Single point mooring

Dimensions

Total length: 121 m(38 mm open link chain)

Sinker5-ton cast iron construction

Figure D.2 WindSentinel installation case example and mooring diagram (continued)

57

(a) Flow of installation work
Figure D.3 MIA installation case example and mooring diagram

58

(b) Mooring diagram(c) Floating body dimensions
Item

Contents

Type

Spar type

Dimensions

Diameter 1.0 m/2.15 m x Length 25 m

Draft

4m

WeightApprox. 46 tons(d) Mooring specifications
Item

Contents

Type

Three-point mooring

Dimensions

Total length: 320 m x 3(Chain 60 m + Synthetic fiber rope 180 m +Chain 80 m)

Anchor5-ton Danforth anchor x 3

Figure D.3 MIA installation case example and mooring diagram (continued)

59

vi