ISO 28902-3:2018

Air quality — Environmental meteorology — Part 3: Ground-based remote sensing of wind by continuous-wave Doppler lidar

This document specifies the requirements and performance test procedures for monostatic heterodyne continuous-wave (CW) Doppler lidar techniques and presents their advantages and limitations. The term "Doppler lidar" used in this document applies solely to monostatic heterodyne CW lidar systems retrieving wind measurements from the scattering of laser light by aerosols in the atmosphere. Performances and limits are described based on standard atmospheric conditions. This document describes the determination of the line-of-sight wind velocity (radial wind velocity). NOTE Derivation of wind vector from individual line-of-sight measurements is not described in this document since it is highly specific to a particular wind lidar configuration. One example of the retrieval of the wind vector can be found in ISO 28902-2:2017, Annex B. This document does not address the retrieval of the wind vector. This document can be used for the following application areas: — meteorological briefing for e.g. aviation, airport safety, marine applications, oil platforms; — wind power production, e.g. site assessment, power curve determination; — routine measurements of wind profiles at meteorological stations; — air pollution dispersion monitoring; — industrial risk management (direct data monitoring or by assimilation into micro-scale flow models); — exchange processes (greenhouse gas emissions). This document can be used by manufacturers of monostatic CW Doppler wind lidars as well as bodies testing and certifying their conformity. This document also provides recommendations for users to make adequate use of these instruments.

Qualité de l'air — Météorologie de l'environnement — Partie 3: Télédétection du vent par lidar Doppler à ondes continues basé au sol

Le présent document spécifie les exigences et les modes opératoires d'essais de performance relatifs aux techniques de lidar Doppler monostatique hétérodyne à ondes continues et présente leurs avantages et limites. Dans le présent document, le terme «lidar Doppler» s'applique uniquement à des systèmes lidars monostatiques hétérodynes à ondes continues permettant d'extraire des mesures du vent à partir de la diffusion d'une lumière laser par des aérosols dans l'atmosphère. Les performances et les limites sont décrites sur la base de conditions atmosphériques normalisées. Le présent document décrit la détermination de la vitesse du vent sur la ligne de visée (vitesse radiale du vent). NOTE La détermination du vecteur vent à partir de mesures individuelles sur la ligne de visée n'est pas décrite dans le présent document car elle est hautement spécifique à une configuration de lidar particulière. Un exemple d'extraction du vecteur vent est donné dans l'ISO 28902-2:2017, Annexe B. Le présent document ne traite pas de l'extraction du vecteur vent. Le présent document peut être utilisé dans les champs d'application suivants: — points météorologiques, par exemple pour l'aviation, la sécurité aéroportuaire, les applications maritimes, les plates-formes pétrolières; — production d'énergie éolienne, par exemple évaluation d'un site, détermination de la courbe de puissance; — mesurages de routine des profils de vent dans les stations météorologiques; — surveillance de la dispersion des polluants dans l'atmosphère; — gestion des risques industriels (surveillance directe des données ou par assimilation des données dans des modèles de flux à micro-échelle); — processus d'échanges (émissions de gaz à effet de serre). Le présent document peut être utilisé par les fabricants de lidars Doppler monostatiques à ondes continues ainsi que par les organismes en charge des essais et de la certification de leur conformité. Le présent document fournit également des recommandations aux utilisateurs pour un usage adéquat de ces instruments.

General Information

• Status: Published
• Publication Date: 13-Nov-2018
• ICS: 07.060 - Geology. Meteorology. Hydrology
• Technical Committee: ISO/TC 146/SC 5 - Meteorology
• Drafting Committee: ISO/TC 146/SC 5/WG 6 - Lidar
• Current Stage: 6060 - International Standard published
• Due Date: 02-Sep-2019
• Completion Date: 14-Nov-2018

Standards Content (Sample)

ISO/TC 146/SC 5
Date: 2018-08
Deleted: /FDIS
ISO 28902-3:2018(E)
ISO/TC 146/SC 5/WG 6
Secretariat: DIN
Air quality — Environmental meteorology — Part 3: Ground-based remote
sensing of wind by heterodyne continuous-wave Doppler lidar
Qualité de l'air — Météorologie de l'environnement — Partie 3: Télédétection du
vent par lidar Doppler à ondes entretenues basée sur le sol
© ISO 2018 – All rights reserved
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ISO 28902-3:2018(E)
© ISO 2018

All rights reserved. Unless otherwise specified, or required in the context of its implementation,

no part of this publication may be reproduced or utilized otherwise in any form or by any means,

electronic or mechanical, including photocopying, or posting on the internet or an intranet,

without prior written permission. Permission can be requested from either ISO at the address

below or ISO's member body in the country of the requester.
ISO Copyright Office
CP 401 • CH‐1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Fax: + 41 22 749 09 47
Email: [e-mail]
Website: www.iso.org
Published in Switzerland.
© ISO 2018 – All rights reserved
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ISO 28902-3:2018(E)
Contents Page

Foreword ........................................................................................................................................................................... v

Introduction ................................................................................................................................................................... vi

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

2  Normative references .................................................................................................................................... 1

3  Terms and definitions .................................................................................................................................... 1

4  Fundamentals of heterodyne Doppler lidar .......................................................................................... 4

4.1  Overview ............................................................................................................................................................. 4

4.2  Heterodyne detection .................................................................................................................................... 6

4.3  Spectral analysis .............................................................................................................................................. 8

4.3.1  Signal processing for CW lidar .................................................................................................................... 8

4.3.2  An example of a wind speed estimation process .................................................................................. 9

4.4  Target variables ............................................................................................................................................... 9

4.5  Sources of noise and uncertainties ........................................................................................................ 10

4.5.1  Local oscillator (LO) shot noise ............................................................................................................... 10

4.5.2  Detector noise ................................................................................................................................................ 10

4.5.3  Relative intensity noise (RIN) .................................................................................................................. 10

4.5.4  Speckles ............................................................................................................................................................ 11

4.5.5  Laser frequency ............................................................................................................................................. 11

4.6  Range assignment ......................................................................................................................................... 11

4.7  Known limitations ........................................................................................................................................ 11

5  System specifications and tests ............................................................................................................... 12

5.1  System specifications .................................................................................................................................. 12

5.1.1  Laser wavelength .......................................................................................................................................... 12

5.1.2  Transmitter/receiver characteristics ................................................................................................... 12

5.1.3  Pointing system characteristics .............................................................................................................. 13

5.2  Figures of merit ............................................................................................................................................. 14

5.3  Precision and availability of measurements ...................................................................................... 14

5.3.1  Radial velocity measurement accuracy ................................................................................................ 14

5.3.2  Data availability ............................................................................................................................................ 14

5.3.3  Maximum operational range .................................................................................................................... 14

5.4  Testing procedures ...................................................................................................................................... 15

5.4.1  General ............................................................................................................................................................. 15

5.4.2  Hard target return ........................................................................................................................................ 15

5.4.3  Assessment of accuracy by intercomparison with other instrumentation ............................. 15

5.4.4  Maximum operational range validation ............................................................................................... 17

6  Measurement planning and installation instructions ..................................................................... 17

6.1  Site requirements ......................................................................................................................................... 17

6.2  Limiting conditions for general operation .......................................................................................... 17

6.3  Maintenance and operational test .......................................................................................................... 18

6.3.1  General ............................................................................................................................................................. 18

6.3.2  Maintenance ................................................................................................................................................... 18

6.3.3  Operational test ............................................................................................................................................. 18

6.3.4  Uncertainty ..................................................................................................................................................... 18

© ISO 2018 – All rights reserved
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ISO 28902-3:2018(E)

Bibliography ................................................................................................................................................................. 20

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ISO 28902-3:2018(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national

standards bodies (ISO member bodies). The work of preparing International Standards is normally

carried out through ISO technical committees. Each member body interested in a subject for which a

technical committee has been established has the right to be represented on that committee.

International organizations, governmental and non‐governmental, in liaison with ISO, also take part in

the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all

matters of electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO’s adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT)

see www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 5,

Meteorology, and by the World Meteorological Organization (WMO) as a common ISO/WMO Standard

under the Agreement on Working Arrangements signed between the WMO and ISO in 2008.

A list of all parts in the ISO 28902 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 28902-3:2018(E)
Introduction

Lidars (“light detection and ranging”), used in this document to designate atmospheric lidars, have

proven to be valuable systems for the remote sensing of atmospheric pollutants in various

meteorological parameters, such as wind, clouds, aerosols and gases. Extensive optical and physical

properties of the probed targets, such as size distribution, chemical composition, shape of the particles

and gas concentration, and optical properties of the atmosphere, such as visibility, extinction and

backscatter, can be retrieved using lidars. Atmospheric targets such as these can be spatially resolved

along their line of sight by, for example, focusing the continuous‐wave beam at the chosen specific

range. The measurements can be carried out without direct contact and in any direction as

electromagnetic radiation is used for sensing the targets. Lidar systems, therefore, supplement the

conventional in situ measurement technology. They are suited for a large number of applications that

cannot be adequately performed by using in situ or point measurement methods.

There are several methods by which lidar can be used to measure atmospheric wind. The four most

[1]

commonly used methods are heterodyne pulsed Doppler wind lidar (see ISO 28902‐2:2017 ),

heterodyne continuous‐wave Doppler wind lidar, direct‐detection Doppler wind lidar and resonance

Doppler wind lidar (commonly used for mesospheric sodium layer measurements). For further reading,

refer to References [2] and [3].

This document describes the use of (monostatic) heterodyne continuous‐wave Doppler lidar.

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ISO 28902-3:2018(E)
Air quality — Environmental meteorology — Part 3: Ground-
based remote sensing of wind by heterodyne continuous-wave
Doppler lidar
1 Scope

This document specifies the requirements and performance test procedures for monostatic heterodyne

continuous‐wave (CW) Doppler lidar techniques and presents their advantages and limitations. The

term “Doppler lidar” used in this document applies solely to monostatic heterodyne CW lidar systems

retrieving wind measurements from the scattering of laser light by aerosols in the atmosphere.

Performances and limits are described based on standard atmospheric conditions. This document

describes the determination of the line‐of‐sight wind velocity (radial wind velocity).

NOTE Derivation of wind vector from individual line‐of‐sight measurements is not described in this

document since it is highly specific to a particular wind lidar configuration. One example of the retrieval of the

wind vector can be found in ISO 28902‐2:2017, Annex B.
This document does not address the retrieval of the wind vector.
This document can be used for the following application areas:

— meteorological briefing for e.g. aviation, airport safety, marine applications, oil platforms;

— wind power production, e.g. site assessment, power curve determination;
— routine measurements of wind profiles at meteorological stations;
— air pollution dispersion monitoring;

— industrial risk management (direct data monitoring or by assimilation into micro‐scale flow

models);
— exchange processes (greenhouse gas emissions).

This document can be used by manufacturers of monostatic CW Doppler wind lidars as well as bodies

testing and certifying their conformity. This document also provides recommendations for users to

make adequate use of these instruments.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

IEC 61400‐12‐1:2017, Wind energy generation systems — Part 12-1: Power performance measurements

of electricity producing wind turbines
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

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ISO 28902-3:2018(E)
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
data availability

ratio between the number of actual considered measurement data with a predefined data quality and

the number of expected measurement data for a given measurement period

Note 1 to entry: In the wind industry, this term commonly applies to measurements averaged over a standard

period of 10 min.
3.2
displayed range resolution
spatial interval between the centres of two successive range measurements
3.3
effective range resolution

application‐related variable describing an integrated range interval for which the target variable is

delivered with a defined uncertainty
[SOURCE: ISO 28902‐1:2012, 3.14, modified — The example has been deleted.]
3.4
effective temporal resolution

application‐related variable describing an integrated time interval for which the target variable is

delivered with a defined uncertainty

[SOURCE: ISO 28902‐1:2012, 3.12, modified — The symbol and the example has been deleted.]

3.5
extinction coefficient

measure of the atmospheric opacity, expressed by the natural logarithm of the ratio of incident light

intensity to transmitted light intensity, per unit light path length
[SOURCE: ISO 28902‐1:2012, 3.10]
3.6
integration time
time spent in order to derive an independent value of the line‐of‐sight velocity
3.7
maximum acquisition range
RMaxA
maximum distance at which a lidar signal can be recorded and processed

Note 1 to entry: It depends primarily on the laser wavelength and transmitter aperture size; also, to some extent,

it depends on the number of acquisition points and the sampling frequency.
3.8
minimum acquisition range
RMinA
minimum distance from which a lidar signal can be recorded and processed
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ISO 28902-3:2018(E)

Note 1 to entry: If the minimum acquisition range is not given, it is assumed to be zero. It can be different from

zero, when the reception is blind by focusing limitations.
3.9
maximum operational range
MaxO

maximum distance to which a wind speed can be derived with confidence from the lidar signal

Note 1 to entry: The maximum operational range is less than or equal to the maximum acquisition range.

Note 2 to entry: The maximum operational range is defined along an axis corresponding to the application. It is

measured vertically for vertical wind profiler. It is measured horizontally for scanning lidars able to measure in

the full hemisphere.

Note 3 to entry: The maximum operational range depends on lidar parameters but also on atmospheric

conditions, particularly the extinction coefficient.
3.10
measurement period
interval of time between the first and last measurements
[SOURCE: ISO 28902‐2:2017, 3.10]
3.11
minimum operational range
MinO

minimum distance where wind speed can be derived with confidence from the lidar signal

Note 1 to entry: The minimum operational range is also called blind range.

Note 2 to entry: In continuous‐wave lidars, the minimum operational range is determined by the closest position

of the focus achievable by the transceiver optical system.
3.12
physical range resolution
width [full width at half maximum (FWHM)] of the range weighting function
[SOURCE: ISO 28902‐2:2017, 3.12]
3.13
probe length

width [full width at half maximum (FWHM)] of the spatial weighting function selecting the region in

space that contributes to the wind speed computation
Note 1 to entry: The probe length is centred on the measurement distance.
3.14
range resolution

equipment‐related variable describing the shortest range interval from which independent signal

information can be obtained
[SOURCE: ISO 28902‐1:2012, 3.13]
3.15
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ISO 28902-3:2018(E)
range weighting function
weighting function of the radial wind speed along the line of sight
[SOURCE: ISO 28902‐2:2017, 3.15]
3.16
temporal resolution

equipment‐related variable describing the shortest time interval from which independent signal

information can be obtained
[SOURCE: ISO 28902‐1:2012, 3.11]
3.17
velocity bias
maximum instrumental offset on the velocity measurement

Note 1 to entry: The velocity bias has to be minimized with adequate calibration, for example, on a fixed target.

[SOURCE: ISO 28902‐2:2017, 3.17]
3.18
velocity range

range determined by the minimum measurable wind speed, the maximum measurable wind speed and

the ability to measure the velocity sign, without ambiguity

Note 1 to entry: Depending on the lidar application, the velocity range can be defined as the radial wind velocity

(scanning lidar) or as horizontal wind velocity (wind profiler).
[SOURCE: ISO 28902‐2:2017, 3.18]
3.19
velocity resolution
instrumental velocity standard deviation

Note 1 to entry: The velocity resolution is determined by the signal processing bin width.

3.20
wind shear
variation of wind speed across a plane perpendicular to the wind direction
[SOURCE: ISO 28902‐2:2017, 3.20]
4 Fundamentals of heterodyne Doppler lidar
4.1 Overview

A CW Doppler lidar emits a narrow laser beam (see Figure 1). As it propagates in the atmosphere, the

laser radiation is scattered in all directions by aerosols, molecules and other scattering material. Part of

the scattered radiation propagates back to the lidar, it is captured by a telescope, detected and analysed.

Since the aerosols and molecules move with the atmosphere, a Doppler shift results, changing the

frequency of the scattered laser light.

At the wavelengths (and thus frequencies) relevant to heterodyne (coherent) Doppler lidar it is the

aerosols that provide the principal target for measurement of the back‐scattered signal.

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ISO 28902-3:2018(E)

The analysis aims at measuring the difference Δf between the frequencies f of the emitted laser pulse

and fr of the backscattered light. According to the Doppler equation, this difference is proportional to

the line‐of‐sight wind component, as shown by Formula (1):
fff2/v  (1)
rt r
where
λ is the laser wavelength;
v

r is the line‐of‐sight wind component (component of the wind vector v along the axis of the laser

beam, counted positive when the wind is blowing away from the lidar).
Key
1 scattering particles moving with the wind
2 optical path of the emitted laser beam
3 optical axis of the receiver
4 lidar instrument
Figure 1 — Measurement principle of a heterodyne Doppler lidar

For a CW Doppler lidar system, the measurement range is usually determined by focusing the beam to

create a waist at the chosen distance. Light backscattered from those regions in close proximity to the

waist is efficiently re‐imaged back into the receiver; light from a significantly closer or greater distance

from the waist or focus is inefficiently gathered.
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ISO 28902-3:2018(E)
4.2 Heterodyne detection

In a heterodyne lidar, the detection of the light captured by the receiving telescope (at frequency

f = f + Δf) is described schematically in Figure 2. The received light is mixed with the beam of a highly

r t

stable, continuous‐wave laser called the local oscillator (LO). The sum of the two electromagnetic waves

– backscattered and local oscillator – is converted into an electrical signal by a quadratic detector

(producing an electrical current proportional to the power of the electromagnetic wave illuminating its

sensitive surface). An analogue, high‐pass filter is then applied for eliminating the low‐frequency

components of the signal, and a low‐pass filter is also applied to avoid problems caused by aliasing in

the subsequent signal processing.
Key
1 detector Circ'r circulator
Inserted Cells
2 laser/local oscillator (LO) w0 beam waist
Inserted Cells
3 receive light ZR Rayleigh length
4 transmit light θ total angular spread
5 single‐mode fibre w(z) function of the axial distance
6 transmit/receiver aperture

7 Gaussian profile transmitted beam and of backpropagated local oscillator (BPLO)

Figure 2 — Principles of heterodyne detection, showing an example CW lidar architecture and

focus geometry

The result is a current i(t) beating at the radio frequency f + Δf – f , as shown by Formula (2) (derived

t lo
from Formula (8) in Reference [5]):
e
it2 Kt tP tP cos2fff tt nt (2)
rlo tlo
hf

i t
het
where
t is the time;
η is the detector quantum efficiency;
e is electrical charge of an electron;
h is Planck’s constant;

K is the instrumental constant taking into account transmission losses through the receiver;

ξ(t) is the random modulation of the signal amplitude by speckles effect (see 4.5.4);

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ISO 28902-3:2018(E)
γ(t) is the heterodyne efficiency;
P(t) is the power of the backscattered light;
P is the power of the local oscillator;
f is the frequency of the local oscillator;
φ(t) is the random phase;
n(t) is the white detection noise;
i (t) is the heterodyne signal.
het

The heterodyne efficiency γ(t) is a measure for the quality of the optical mixing of the backscattered and

the local oscillator wave fields on the surface of the detector. It cannot exceed 1. A good heterodyne

efficiency requires a careful sizing and alignment of the local oscillator relative to the backscattered

wave. Optimal mixing conditions are discussed in Reference [5]. The heterodyne efficiency is not a

purely instrumental function, it also depends on the on the refractive index turbulence (Cn) along the

[6]

laser beam . Under conditions of strong atmospheric turbulence, the effect on varying the refractive

index degrades the heterodyne efficiency. This can happen when the lidar is operated close to the

ground during a hot sunny day.

For a CW coherent system, the time‐averaged optical signal power, P, backscattered by the aerosols

[7][8]
into the receiver is given to a good approximation by Formula (3):
PP  (3)

where P is the transmitted laser power and β(π) is the atmospheric backscatter coefficient in 1/(m·sr).

It is notable that P is independent of both the focus range and the system aperture size. This

approximation starts to break down as the system approaches its maximum operating range. With a

value of 10 ·1/(m·sr) for β(π) in clear boundary‐layer air, and a transmitted power of P ~ 1 W and λ ~

1,55 µm, the received power PS derived is of order 50 fW, emphasizing the need for extremely high

sensitivity.

The signal‐to‐noise ratio (SNR) for a wind speed measurement by a continuous‐wave coherent wind

lidar is given by Formula (4):
SNR (4)
vD1 vRv

where η is an efficiency term incorporating optical losses and photodetector sensitivity (typically η ~

0,5, approaching unity only for a “perfect” system), P is the input signal power and (hc/λ) is the light

−19

quantum energy, of order 1,3·10 J at wavelength 1,55 µm. The signal bandwidth Δv is determined by

three contributions (instrumental width, transit time broadening and turbulence broadening), and the

term inside the brackets denotes the various noise sources. D(v) and R(v) represent the power spectral

density (at frequency v) from dark noise and RIN, respectively, in units of the power spectral density of

the local oscillator shot noise. Ideally D(v) and R(v) should both be << 1 over the range of Doppler

frequencies of principal interest, so that shot noise is the dominant noise source.

The SNR as defined here is the power spectral density at the Doppler peak divided by that in the

surrounding noise floor. The averaging of many spectra (described in the following clauses) ensures

that good performance can be obtained even when the SNR is well below unity. For example, in a case

where 4 000 spectra have been averaged at a SNR of 0,1, the resulting peak in the Doppler spectrum

will easily exceed a 5 standard deviations (5σ) threshold level above the noise floor. From the above, it

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ISO 28902-3:2018(E)
−9 −1 −1

is possible to derive an approximate value of β(π) ~ 10 m sr for the minimum detectable

min

backscatter, assuming a transmitted intensity of 1 W and a 20 ms measurement time.

NOTE In the lidar community, SNR is commonly, and more properly, referred to as the carrier‐to‐noise ratio

(CNR).
4.3 Spectral analysis
4.3.1 Signal processing for CW lidar

The retrieval of the radial velocity measurement from heterodyne signals requires a frequency analysis.

This is conventionally done in the digital domain after analogue‐to‐digital conversion of the heterodyne

signals. An overview of a possible processing scheme is given in Figure 3. An analogue to digital

converter (ADC) with a sampling rate of 100 MHz permits spectral analysis up to a maximum frequency

of 50 MHz, corresponding to a wind speed V of ~38,8 m/s for an upwardly pointing 30° scan (with

LOS

λ = 1,55 µm). An analogue low‐pass filter with a cut‐off frequency of 50 MHz, inserted between the

detector and ADC, eliminates aliasing. Spectra are calculated by digital Fourier transform (DFT)

methods; a 512 point DFT gives rise to 256 points in the output spectrum with a bin width of ∼200 kHz,

corresponding to a line‐of‐sight velocity range of ∼0,15 m/s. Each DFT represents ∼5 µs of data;

successive DFTs are then calculated, and the resulting “voltage” spectra are squared in order to

generate a power spectrum. These power spectra are then averaged to find a mean spectrum for the

averaging period. The random fluctuation in the shot noise floor of the spectrum reduces as the square

root of the number of averages and hence the detection sensitivity increases by the same factor. For

4 000 averages, the measurement time amounts to ∼20 ms (a data rate of ~50 Hz). This requires that

the processing is capable of a 100 % duty cycle, which can be achieved, for example, with a fast Fourier

transform (FFT) block within a field‐programmable gate array (FPGA). It has bee
...

INTERNATIONAL ISO
STANDARD 28902-3
First edition
2018-11
Air quality — Environmental
meteorology —
Part 3:
Ground-based remote sensing of wind
by continuous-wave Doppler lidar
Qualité de l'air — Météorologie de l'environnement —
Partie 3: Télédétection du vent par lidar Doppler à ondes contenues
basé au sol
Reference number
ISO 28902-3:2018(E)
ISO 2018
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ISO 28902-3:2018(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2018

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 28902-3:2018(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

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

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Fundamentals of heterodyne Doppler lidar ............................................................................................................................ 4

4.1 Overview ...................................................................................................................................................................................................... 4

4.2 Heterodyne detection ........................................................................................................................................................................ 5

4.3 Spectral analysis .................................................................................................................................................................................... 7

4.3.1 Signal processing for CW lidar ............................................................................................................................. 7

4.3.2 An example of a wind speed estimation process ................................................................................. 9

4.4 Target variables ...................................................................................................................................................................................... 9

4.5 Sources of noise and uncertainties ........................................................................................................................................ 9

4.5.1 Local oscillator shot noise ....................................................................................................................................... 9

4.5.2 Detector noise .................................................................................................................................................................10

4.5.3 Relative intensity noise ...........................................................................................................................................10

4.5.4 Speckles ................................................................................................................................................................................10

4.5.5 Laser frequency .............................................................................................................................................................10

4.6 Range assignment .............................................................................................................................................................................10

4.7 Known limitations .............................................................................................................................................................................11

5 System specifications and tests ..........................................................................................................................................................12

5.1 System specifications .....................................................................................................................................................................12

5.1.1 Laser wavelength ..........................................................................................................................................................12

5.1.2 Transmitter/receiver characteristics ..........................................................................................................12

5.1.3 Pointing system characteristics .......................................................................................................................12

5.2 Figures of merit ...................................................................................................................................................................................13

5.3 Precision and availability of measurements ...............................................................................................................13

5.3.1 Radial velocity measurement accuracy .....................................................................................................13

5.3.2 Data availability .............................................................................................................................................................14

5.3.3 Maximum operational range ..............................................................................................................................14

5.4 Testing procedures ...........................................................................................................................................................................14

5.4.1 General...................................................................................................................................................................................14

5.4.2 Hard target return .......................................................................................................................................................14

5.4.3 Assessment of accuracy by intercomparison with other instrumentation ................14

5.4.4 Maximum operational range validation....................................................................................................16

6 Measurement planning and installation instructions ................................................................................................16

6.1 Site requirements ..............................................................................................................................................................................16

6.2 Limiting conditions for general operation ...................................................................................................................17

6.3 Maintenance and operational test .......................................................................................................................................17

6.3.1 General...................................................................................................................................................................................17

6.3.2 Maintenance .....................................................................................................................................................................17

6.3.3 Operational test .............................................................................................................................................................17

6.3.4 Uncertainty ........................................................................................................................................................................18

Bibliography .............................................................................................................................................................................................................................19

© ISO 2018 – All rights reserved iii
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ISO 28902-3:2018(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www. iso. org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www. iso.o rg/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO’s adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www. iso

.org/iso/foreword. html.

This document was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 5,

Meteorology.
A list of all parts in the ISO 28902 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www. iso. org/members. html.
iv © ISO 2018 – All rights reserved
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ISO 28902-3:2018(E)
Introduction

Lidars (“light detection and ranging”), used in this document to designate atmospheric lidars,

have proven to be valuable systems for the remote sensing of atmospheric pollutants in various

meteorological parameters, such as wind, clouds, aerosols and gases. Extensive optical and physical

properties of the probed targets, such as size distribution, chemical composition, shape of the particles

and gas concentration, and optical properties of the atmosphere, such as visibility, extinction and

backscatter, can be retrieved using lidars. Atmospheric targets such as these can be spatially resolved

along their line of sight by, for example, focusing the continuous-wave beam at the chosen specific range.

The measurements can be carried out without direct contact and in any direction as electromagnetic

radiation is used for sensing the targets. Lidar systems, therefore, supplement the conventional in situ

measurement technology. They are suited for a large number of applications that cannot be adequately

performed by using in situ or point measurement methods.

There are several methods by which lidar can be used to measure atmospheric wind. The four most

[1]

commonly used methods are heterodyne pulsed Doppler wind lidar (see ISO 28902-2:2017 ),

heterodyne continuous-wave Doppler wind lidar, direct-detection Doppler wind lidar and resonance

Doppler wind lidar (commonly used for mesospheric sodium layer measurements). For further reading,

refer to References [2] and [3].

This document describes the use of (monostatic) heterodyne continuous-wave Doppler lidar.

© ISO 2018 – All rights reserved v
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INTERNATIONAL STANDARD ISO 28902-3:2018(E)
Air quality — Environmental meteorology —
Part 3:
Ground-based remote sensing of wind by continuous-wave
Doppler lidar
1 Scope

This document specifies the requirements and performance test procedures for monostatic heterodyne

continuous-wave (CW) Doppler lidar techniques and presents their advantages and limitations. The

term “Doppler lidar” used in this document applies solely to monostatic heterodyne CW lidar systems

retrieving wind measurements from the scattering of laser light by aerosols in the atmosphere.

Performances and limits are described based on standard atmospheric conditions. This document

describes the determination of the line-of-sight wind velocity (radial wind velocity).

NOTE Derivation of wind vector from individual line-of-sight measurements is not described in this

document since it is highly specific to a particular wind lidar configuration. One example of the retrieval of the

wind vector can be found in ISO 28902-2:2017, Annex B.
This document does not address the retrieval of the wind vector.
This document can be used for the following application areas:

— meteorological briefing for e.g. aviation, airport safety, marine applications, oil platforms;

— wind power production, e.g. site assessment, power curve determination;
— routine measurements of wind profiles at meteorological stations;
— air pollution dispersion monitoring;

— industrial risk management (direct data monitoring or by assimilation into micro-scale flow

models);
— exchange processes (greenhouse gas emissions).

This document can be used by manufacturers of monostatic CW Doppler wind lidars as well as bodies

testing and certifying their conformity. This document also provides recommendations for users to

make adequate use of these instruments.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

IEC 61400-12-1:2017, Wind energy generation systems — Part 12-1: Power performance measurements of

electricity producing wind turbines
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
© ISO 2018 – All rights reserved 1
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ISO 28902-3:2018(E)

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
data availability

ratio between the number of actual considered measurement data with a predefined data quality and

the number of expected measurement data for a given measurement period

Note 1 to entry: In the wind industry, this term commonly applies to measurements averaged over a standard

period of 10 min.
3.2
displayed range resolution
spatial interval between the centres of two successive range measurements
3.3
effective range resolution

application-related variable describing an integrated range interval for which the target variable is

delivered with a defined uncertainty
[SOURCE: ISO 28902-1:2012, 3.14, modified — The example has been deleted.]
3.4
effective temporal resolution

application-related variable describing an integrated time interval for which the target variable is

delivered with a defined uncertainty

[SOURCE: ISO 28902-1:2012, 3.12, modified — The symbol and the example has been deleted.]

3.5
extinction coefficient

measure of the atmospheric opacity, expressed by the natural logarithm of the ratio of incident light

intensity to transmitted light intensity, per unit light path length
[SOURCE: ISO 28902-1:2012, 3.10]
3.6
integration time
time spent in order to derive an independent value of the line-of-sight velocity
3.7
maximum acquisition range
MaxA
maximum distance at which a lidar signal can be recorded and processed

Note 1 to entry: It depends primarily on the laser wavelength and transmitter aperture size; also, to some extent,

it depends on the number of acquisition points and the sampling frequency.
3.8
minimum acquisition range
MinA
minimum distance from which a lidar signal can be recorded and processed

Note 1 to entry: If the minimum acquisition range is not given, it is assumed to be zero. It can be different from

zero, when the reception is blind by focusing limitations.
2 © ISO 2018 – All rights reserved
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ISO 28902-3:2018(E)
3.9
maximum operational range
MaxO

maximum distance to which a wind speed can be derived with confidence from the lidar signal

Note 1 to entry: The maximum operational range is less than or equal to the maximum acquisition range.

Note 2 to entry: The maximum operational range is defined along an axis corresponding to the application. It is

measured vertically for vertical wind profiler. It is measured horizontally for scanning lidars able to measure in

the full hemisphere.

Note 3 to entry: The maximum operational range depends on lidar parameters but also on atmospheric

conditions, particularly the extinction coefficient.
3.10
measurement period
interval of time between the first and last measurements
[SOURCE: ISO 28902-2:2017, 3.10]
3.11
minimum operational range
MinO

minimum distance where wind speed can be derived with confidence from the lidar signal

Note 1 to entry: The minimum operational range is also called blind range.

Note 2 to entry: In continuous-wave lidars, the minimum operational range is determined by the closest position

of the focus achievable by the transceiver optical system.
3.12
physical range resolution
width [full width at half maximum (FWHM)] of the range weighting function
[SOURCE: ISO 28902-2:2017, 3.12]
3.13
probe length

width [full width at half maximum (FWHM)] of the spatial weighting function selecting the region in

space that contributes to the wind speed computation
Note 1 to entry: The probe length is centred on the measurement distance.
3.14
range resolution

equipment-related variable describing the shortest range interval from which independent signal

information can be obtained
[SOURCE: ISO 28902-1:2012, 3.13]
3.15
range weighting function
weighting function of the radial wind speed along the line of sight
[SOURCE: ISO 28902-2:2017, 3.15]
3.16
temporal resolution

equipment-related variable describing the shortest time interval from which independent signal

information can be obtained
[SOURCE: ISO 28902-1:2012, 3.11]
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ISO 28902-3:2018(E)
3.17
velocity bias
maximum instrumental offset on the velocity measurement

Note 1 to entry: The velocity bias has to be minimized with adequate calibration, for example, on a fixed target.

[SOURCE: ISO 28902-2:2017, 3.17]
3.18
velocity range

range determined by the minimum measurable wind speed, the maximum measurable wind speed and

the ability to measure the velocity sign, without ambiguity

Note 1 to entry: Depending on the lidar application, the velocity range can be defined as the radial wind velocity

(scanning lidar) or as horizontal wind velocity (wind profiler).
[SOURCE: ISO 28902-2:2017, 3.18]
3.19
velocity resolution
instrumental velocity standard deviation

Note 1 to entry: The velocity resolution is determined by the signal processing bin width.

3.20
wind shear
variation of wind speed across a plane perpendicular to the wind direction
[SOURCE: ISO 28902-2:2017, 3.20]
4 Fundamentals of heterodyne Doppler lidar
4.1 Overview

A CW Doppler lidar emits a narrow laser beam (see Figure 1). As it propagates in the atmosphere,

the laser radiation is scattered in all directions by aerosols, molecules and other scattering material.

Part of the scattered radiation propagates back to the lidar, it is captured by a telescope, detected and

analysed. Since the aerosols and molecules move with the atmosphere, a Doppler shift results, changing

the frequency of the scattered laser light.

At the wavelengths (and thus frequencies) relevant to heterodyne (coherent) Doppler lidar it is the

aerosols that provide the principal target for measurement of the back-scattered signal.

The analysis aims at measuring the difference Δf between the frequencies f of the emitted laser pulse

and f of the backscattered light. According to the Doppler equation, this difference is proportional to

the line-of-sight wind component, as shown by Formula (1):
Δ=ff −=fv−2/λ (1)
rt r
where
λ is the laser wavelength;

is the line-of-sight wind component (component of the wind vector v along the axis of the

laser beam, counted positive when the wind is blowing away from the lidar).
4 © ISO 2018 – All rights reserved
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ISO 28902-3:2018(E)
Key
1 scattering particles moving with the wind
2 optical path of the emitted laser beam
3 optical axis of the receiver
4 lidar instrument
Figure 1 — Measurement principle of a heterodyne Doppler lidar

For a CW Doppler lidar system, the measurement range is usually determined by focusing the beam to

create a waist at the chosen distance. Light backscattered from those regions in close proximity to the

waist is efficiently re-imaged back into the receiver; light from a significantly closer or greater distance

from the waist or focus is inefficiently gathered.
4.2 Heterodyne detection

In a heterodyne lidar, the detection of the light captured by the receiving telescope (at frequency

f = f + Δf ) is described schematically in Figure 2. The received light is mixed with the beam of a highly

r t

stable, continuous-wave laser called the local oscillator (LO). The sum of the two electromagnetic waves

– backscattered and local oscillator – is converted into an electrical signal by a quadratic detector

(producing an electrical current proportional to the power of the electromagnetic wave illuminating

its sensitive surface). An analogue, high-pass filter is then applied for eliminating the low-frequency

components of the signal, and a low-pass filter is also applied to avoid problems caused by aliasing in

the subsequent signal processing.
© ISO 2018 – All rights reserved 5
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ISO 28902-3:2018(E)
Key
1 detector Circ'r circulator
2 laser/local oscillator (LO) w beam waist
3 receive light Z Rayleigh length
4 transmit light θ total angular spread
5 single-mode fibre w(z) function of the axial distance
6 transmit/receiver aperture

7 Gaussian profile transmitted beam and of backpropagated local oscillator (BPLO)

Figure 2 — Principles of heterodyne detection, showing an example CW lidar architecture and

focus geometry

The result is a current i(t) beating at the radio frequency f + Δf – f , as shown by Formula (2) (derived

t lo
from Formula (8) in Reference [5]):
η⋅e
it =⋅22⋅⋅Ktξγ⋅ tP⋅ tP⋅⋅cos π Δ+ff − ft⋅+ϕ t +nt (2)
() () () () ()() (() ()
rlot lo
hf⋅

i ()t
het
where
t is the time;
η is the detector quantum efficiency;
e is electrical charge of an electron;
h is Planck’s constant;

K is the instrumental constant taking into account transmission losses through the receiver;

ξ(t) is the random modulation of the signal amplitude by speckles effect (see 4.5.4);

γ(t) is the heterodyne efficiency;
P (t) is the power of the backscattered light;
P is the power of the local oscillator;
f is the frequency of the local oscillator;
φ(t) is the random phase;
n(t) is the white detection noise;
i (t) is the heterodyne signal.
het
6 © ISO 2018 – All rights reserved
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ISO 28902-3:2018(E)

The heterodyne efficiency γ(t) is a measure for the quality of the optical mixing of the backscattered

and the local oscillator wave fields on the surface of the detector. It cannot exceed 1. A good heterodyne

efficiency requires a careful sizing and alignment of the local oscillator relative to the backscattered

wave. Optimal mixing conditions are discussed in Reference [5]. The heterodyne efficiency is not a

purely instrumental function, it also depends on the on the refractive index turbulence (Cn ) along the

[6]

laser beam . Under conditions of strong atmospheric turbulence, the effect on varying the refractive

index degrades the heterodyne efficiency. This can happen when the lidar is operated close to the

ground during a hot sunny day.

For a CW coherent system, the time-averaged optical signal power, P , backscattered by the aerosols

[7][8]
into the receiver is given to a good approximation by Formula (3):
PP=ππβλ (3)

where P is the transmitted laser power and β(π) is the atmospheric backscatter coefficient in 1/(m·sr).

It is notable that P is independent of both the focus range and the system aperture size. This

approximation starts to break down as the system approaches its maximum operating range. With a

value of 10 ·1/(m·sr) for β(π) in clear boundary-layer air, and a transmitted power of P ~ 1 W and

λ ~ 1,55 µm, the received power P derived is of order 50 fW, emphasizing the need for extremely high

sensitivity.

The signal-to-noise ratio (SNR) for a wind speed measurement by a continuous-wave coherent wind

lidar is given by Formula (4):
SNR= (4)
Δ+vD1 vR+ v
() ()

where η is an efficiency term incorporating optical losses and photodetector sensitivity (typically η ~

0,5, approaching unity only for a “perfect” system), P is the input signal power and (hc/λ) is the light

−19

quantum energy, of order 1,3·10 J at wavelength 1,55 µm. The signal bandwidth Δv is determined by

three contributions (instrumental width, transit time broadening and turbulence broadening), and the

term inside the brackets denotes the various noise sources. D(v) and R(v) represent the power spectral

density (at frequency v) from dark noise and RIN, respectively, in units of the power spectral density

of the local oscillator shot noise. Ideally D(v) and R(v) should both be << 1 over the range of Doppler

frequencies of principal interest, so that shot noise is the dominant noise source.

The SNR as defined here is the power spectral density at the Doppler peak divided by that in the

surrounding noise floor. The averaging of many spectra (described in the following clauses) ensures

that good performance can be obtained even when the SNR is well below unity. For example, in a case

where 4 000 spectra have been averaged at a SNR of 0,1, the resulting peak in the Doppler spectrum

will easily exceed a 5 standard deviations (5σ) threshold level above the noise floor. From the above,

−9 −1 −1

it is possible to derive an approximate value of β(π) ~ 10 m sr for the minimum detectable

min

backscatter, assuming a transmitted intensity of 1 W and a 20 ms measurement time.

NOTE In the lidar community, SNR is commonly, and more properly, referred to as the carrier-to-noise

ratio (CNR).
4.3 Spectral analysis
4.3.1 Signal processing for CW lidar

The retrieval of the radial velocity measurement from heterodyne signals requires a frequency

analysis. This is conventionally done in the digital domain after analogue-to-digital conversion of the

heterodyne signals. An overview of a possible processing scheme is given in Figure 3. An analogue to

digital converter (ADC) with a sampling rate of 100 MHz permits spectral analysis up to a maximum

frequency of 50 MHz, corresponding to a wind speed V of ~38,8 m/s for an upwardly pointing

LOS

30° scan (with λ = 1,55 µm). An analogue low-pass filter with a cut-off frequency of 50 MHz, inserted

© ISO 2018 – All rights reserved 7
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ISO 28902-3:2018(E)

between the detector and ADC, eliminates aliasing. Spectra are calculated by digital Fourier transform

(DFT) methods; a 512 point DFT gives rise to 256 points in the output spectrum with a bin width of

∼200 kHz, corresponding to a line-of-sight velocity range of ∼0,15 m/s. Each DFT represents ∼5 µs

of data; successive DFTs are then calculated, and the resulting “voltage” spectra are squared in order

to generate a power spectrum. These power spectra are then aver
...

NORME ISO
INTERNATIONALE 28902-3
Première édition
2018-11
Qualité de l'air — Météorologie de
l'environnement —
Partie 3:
Télédétection du vent par lidar
Doppler à ondes contenues basé au sol
Air quality — Environmental meteorology —
Part 3: Ground-based remote sensing of wind by continuous-wave
Doppler lidar
Numéro de référence
ISO 28902-3:2018(F)
ISO 2018
---------------------- Page: 1 ----------------------
ISO 28902-3:2018(F)
DOCUMENT PROTÉGÉ PAR COPYRIGHT
© ISO 2018

Tous droits réservés. Sauf prescription différente ou nécessité dans le contexte de sa mise en œuvre, aucune partie de cette

publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique,

y compris la photocopie, ou la diffusion sur l’internet ou sur un intranet, sans autorisation écrite préalable. Une autorisation peut

être demandée à l’ISO à l’adresse ci-après ou au comité membre de l’ISO dans le pays du demandeur.

ISO copyright office
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Web: www.iso.org
Publié en Suisse
ii © ISO 2018 – Tous droits réservés
---------------------- Page: 2 ----------------------
ISO 28902-3:2018(F)
Sommaire Page

Avant-propos ..............................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Domaine d’application ................................................................................................................................................................................... 1

2 Références normatives ................................................................................................................................................................................... 1

3 Termes et définitions ....................................................................................................................................................................................... 2

4 Principes essentiels du lidar Doppler hétérodyne ........................................................................................................... 4

4.1 Présentation générale ....................................................................................................................................................................... 4

4.2 Détection hétérodyne ........................................................................................................................................................................ 6

4.3 Analyse spectrale .................................................................................................................................................................................. 8

4.3.1 Traitement du signal pour un lidar à ondes continues ................................................................... 8

4.3.2 Exemple de processus d’estimation de la vitesse du vent ........................................................... 9

4.4 Variables cibles ....................................................................................................................................................................................10

4.5 Sources de bruit et d’incertitudes .......................................................................................................................................10

4.5.1 Bruit de Schottky de l’oscillateur local ......................................................................................................10

4.5.2 Bruit du détecteur .................. .................................................... ..................................................................................10

4.5.3 Bruit d’intensité relatif (RIN) .............................................................................................................................11

4.5.4 Chatoiement ......................................................................................................................................................................11

4.5.5 Fréquence du laser ......................................................................................................................................................11

4.6 Assignation en distance ................................................................................................................................................................11

4.7 Limites connues ..................................................................................................................................................................................12

5 Spécifications et essais du système ................................................................................................................................................13

5.1 Spécifications du système...........................................................................................................................................................13

5.1.1 Longueur d’onde du laser .....................................................................................................................................13

5.1.2 Caractéristiques de l’émetteur/récepteur ..............................................................................................13

5.1.3 Caractéristiques du système de pointage ................................................................................................13

5.2 Facteurs de mérite ............................................................................................................................................................................14

5.3 Fidélité et disponibilité des mesurages ..........................................................................................................................14

5.3.1 Exactitude de mesure de la vitesse radiale ............................................................................................14

5.3.2 Taux de disponibilité des données ................................................................................................................15

5.3.3 Portée opérationnelle maximale .....................................................................................................................15

5.4 Modes opératoires d’essai ..........................................................................................................................................................15

5.4.1 Généralités .........................................................................................................................................................................15

5.4.2 Écho sur cible dure......................................................................................................................................................15

5.4.3 Évaluation de l’exactitude par comparaison avec d’autres instruments ......................16

5.4.4 Validation de la portée opérationnelle maximale ............................................................................17

6 Planification du mesurage et instructions relatives à l’installation ............................................................18

6.1 Exigences relatives au site..........................................................................................................................................................18

6.2 Conditions limites pour usage général ............................................................................................................................18

6.3 Maintenance et essai de fonctionnement......................................................................................................................19

6.3.1 Généralités .........................................................................................................................................................................19

6.3.2 Maintenance .....................................................................................................................................................................19

6.3.3 Essai de fonctionnement ........................................................................................................................................19

6.3.4 Incertitude ..........................................................................................................................................................................19

Bibliographie ...........................................................................................................................................................................................................................21

© ISO 2018 – Tous droits réservés iii
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ISO 28902-3:2018(F)
Avant-propos

L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes

nationaux de normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est

en général confiée aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude

a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,

gouvernementales et non gouvernementales, en liaison avec l'ISO participent également aux travaux.

L'ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui

concerne la normalisation électrotechnique.

Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont

décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents

critères d'approbation requis pour les différents types de documents ISO. Le présent document a été

rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir www

.iso. org/directives).

L'attention est attirée sur le fait que certains des éléments du présent document peuvent faire l'objet de

droits de propriété intellectuelle ou de droits analogues. L'ISO ne saurait être tenue pour responsable

de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant

les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de

l'élaboration du document sont indiqués dans l'Introduction et/ou dans la liste des déclarations de

brevets reçues par l'ISO (voir www. iso. org/brevets).

Les appellations commerciales éventuellement mentionnées dans le présent document sont données

pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un

engagement.

Pour une explication de la nature volontaire des normes, la signification des termes et expressions

spécifiques de l'ISO liés à l'évaluation de la conformité, ou pour toute information au sujet de l'adhésion

de l'ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles

techniques au commerce (OTC), voir www. iso. org/avant-p ropos.

Le présent document a été élaboré par le comité technique ISO/TC 146, Qualité de l’air, sous-comité SC 5,

Météorologie.

Une liste de toutes les parties de la série ISO 28902 se trouve sur le site web de l’ISO.

Il convient que l’utilisateur adresse tout retour d’information ou toute question concernant le présent

document à l’organisme national de normalisation de son pays. Une liste exhaustive desdits organismes se

trouve à l’adresse www. iso. org/fr/members. html.
iv © ISO 2018 – Tous droits réservés
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ISO 28902-3:2018(F)
Introduction

Les lidars («light detection and ranging»), désignant les lidars atmosphériques dans le présent document,

se sont révélés être des systèmes intéressants pour la télédétection des polluants atmosphériques et

divers paramètres météorologiques, tels que le vent, les nuages, les aérosols et les gaz. L’utilisation des

méthodes lidar permet d’extraire et de déterminer l’ensemble des propriétés optiques et physiques des

cibles explorées telles que la distribution granulométrique, la composition chimique et la forme des

particules, la concentration de gaz, et des propriétés optiques de l’atmosphère telles que la visibilité,

l’extinction et la rétrodiffusion. La détection de telles cibles atmosphériques peut être résolue en

distance le long de la ligne de visée du lidar, par exemple en focalisant le faisceau laser à la distance

choisie. La mesure est sans contact direct et peut se faire dans n’importe quelle direction grâce à

l’utilisation d’un rayonnement électromagnétique. Les systèmes lidar complètent donc les technologies

de mesure in situ classiques. Ils peuvent être utilisés pour plusieurs applications qui ne peuvent pas

être correctement mises en œuvre avec des méthodes de mesure in situ ou ponctuelles.

Plusieurs méthodes permettent d’utiliser les lidars pour mesurer le vent atmosphérique.

Les quatre méthodes les plus couramment utilisées sont le lidar Doppler pulsé hétérodyne

[1]

(voir l’ISO 28902-2:2017 ), le lidar Doppler hétérodyne à ondes continues, le lidar Doppler à détection

directe et le lidar Doppler à résonance (couramment utilisé pour les mesurages de la couche de sodium

mésosphérique). Pour de plus amples informations, se reporter aux Références [2] et [3].

Le présent document décrit l’utilisation du lidar Doppler (monostatique) hétérodyne à ondes continues.

© ISO 2018 – Tous droits réservés v
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NORME INTERNATIONALE ISO 28902-3:2018(F)
Qualité de l'air — Météorologie de l'environnement —
Partie 3:
Télédétection du vent par lidar Doppler à ondes contenues
basé au sol
1 Domaine d’application

Le présent document spécifie les exigences et les modes opératoires d’essais de performance relatifs aux

techniques de lidar Doppler monostatique hétérodyne à ondes continues et présente leurs avantages

et limites. Dans le présent document, le terme «lidar Doppler» s’applique uniquement à des systèmes

lidars monostatiques hétérodynes à ondes continues permettant d’extraire des mesures du vent à

partir de la diffusion d’une lumière laser par des aérosols dans l’atmosphère. Les performances et les

limites sont décrites sur la base de conditions atmosphériques normalisées. Le présent document décrit

la détermination de la vitesse du vent sur la ligne de visée (vitesse radiale du vent).

NOTE La détermination du vecteur vent à partir de mesures individuelles sur la ligne de visée n’est pas

décrite dans le présent document car elle est hautement spécifique à une configuration de lidar particulière. Un

exemple d’extraction du vecteur vent est donné dans l’ISO 28902-2:2017, Annexe B.

Le présent document ne traite pas de l’extraction du vecteur vent.
Le présent document peut être utilisé dans les champs d’application suivants:

— points météorologiques, par exemple pour l’aviation, la sécurité aéroportuaire, les applications

maritimes, les plates-formes pétrolières;

— production d’énergie éolienne, par exemple évaluation d’un site, détermination de la courbe de

puissance;
— mesurages de routine des profils de vent dans les stations météorologiques;
— surveillance de la dispersion des polluants dans l’atmosphère;

— gestion des risques industriels (surveillance directe des données ou par assimilation des données

dans des modèles de flux à micro-échelle);
— processus d’échanges (émissions de gaz à effet de serre).

Le présent document peut être utilisé par les fabricants de lidars Doppler monostatiques à ondes

continues ainsi que par les organismes en charge des essais et de la certification de leur conformité. Le

présent document fournit également des recommandations aux utilisateurs pour un usage adéquat de

ces instruments.
2 Références normatives

Les documents suivants sont cités dans le texte de sorte qu’ils constituent, pour tout ou partie de leur

contenu, des exigences du présent document. Pour les références datées, seule l’édition citée s’applique.

Pour les références non datées, la dernière édition du document de référence s'applique (y compris les

éventuels amendements).

IEC 61400-12-1:2017, Systèmes de génération d’énergie éolienne — Partie 12-1: Mesures de performance de

puissance des éoliennes de production d’électricité
© ISO 2018 – Tous droits réservés 1
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ISO 28902-3:2018(F)
3 Termes et définitions

Pour les besoins du présent document, les termes et définitions suivants s’appliquent.

L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en

normalisation, consultables aux adresses suivantes:

— ISO Online browsing platform: disponible à l’adresse https: //www .iso .org/obp

— IEC Electropedia: disponible à l’adresse http: //www .electropedia .org/
3.1
taux de disponibilité des données

rapport entre le nombre de données de mesure effectivement acquises ayant une qualité prédéfinie et

le nombre attendu de données de mesure pendant une période de mesure donnée

Note 1 à l'article: Dans l’industrie éolienne, ce terme s’applique couramment à des mesurages moyennés sur une

période normalisée de 10 min.
3.2
résolution en portée affichée
intervalle spatial entre les centres de deux mesurages de portée successifs
3.3
résolution en portée effective

variable liée à l’application décrivant un intervalle de portée intégré pour lequel la variable cible est

fournie avec une incertitude définie
[SOURCE: ISO 28902-1:2012, 3.14, modifiée — L’exemple a été supprimé.]
3.4
résolution temporelle effective

variable liée à l’application décrivant un intervalle de temps intégré pour lequel la variable cible est

fournie avec une incertitude définie

[SOURCE: ISO 28902-1:2012, 3.12, modifiée — Le symbole et l’exemple ont été supprimés.]

3.5
coefficient d’extinction

mesure de l’opacité atmosphérique, exprimée par le logarithme népérien du rapport de l’intensité

lumineuse incidente à l’intensité lumineuse transmise, par longueur unitaire du trajet lumineux

[SOURCE: ISO 28902-1:2012, 3.10]
3.6
durée d’intégration

temps nécessaire à la détermination d’une valeur indépendante de la vitesse dans la ligne de visée

3.7
portée maximale d’acquisition
MaxA
distance maximale à laquelle un signal lidar peut être enregistré et traité

Note 1 à l'article: Elle dépend principalement de la longueur d’onde du laser et de la dimension de l’ouverture de

l’émetteur; elle dépend aussi, dans une certaine mesure, du nombre de points d’acquisition et de la fréquence

d’échantillonnage.
2 © ISO 2018 – Tous droits réservés
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ISO 28902-3:2018(F)
3.8
portée minimale d’acquisition
MinA

distance minimale à partir de laquelle un signal lidar peut être enregistré et traité

Note 1 à l'article: Si la portée minimale d’acquisition n’est pas indiquée, elle est supposée être égale à zéro. Elle

peut être différente de zéro lorsque la réception est masquée par les limites de focalisation.

3.9
portée opérationnelle maximale
MaxO

distance maximale jusqu’à laquelle le signal lidar permet de déterminer de manière fiable une

vitesse de vent

Note 1 à l'article: La portée opérationnelle maximale est inférieure ou égale à la portée maximale d’acquisition.

Note 2 à l'article: La portée opérationnelle maximale est définie le long d’un axe correspondant à l’application.

Elle est mesurée verticalement pour un profileur de vent. Elle est mesurée horizontalement pour les lidars à

balayage capables de mesurer dans la totalité d’un hémisphère.

Note 3 à l'article: La portée opérationnelle maximale dépend des paramètres lidar, mais aussi des conditions

atmosphériques, en particulier du coefficient d’extinction.
3.10
période de mesure
intervalle de temps entre les première et dernière mesures
[SOURCE: ISO 28902-2:2017, 3.10]
3.11
portée opérationnelle minimale
MinO

distance minimale à laquelle le signal lidar permet de déterminer de manière fiable une vitesse de vent

Note 1 à l'article: La portée opérationnelle minimale est également appelée zone aveugle.

Note 2 à l'article: Dans les lidars à ondes continues, la portée opérationnelle minimale est déterminée par la

position la plus proche du foyer pouvant être atteinte par le système optique de l’émetteur/récepteur.

3.12
résolution en portée physique
largeur (à mi-hauteur) de la fonction de pondération en portée
[SOURCE: ISO 28902-2:2017, 3.12]
3.13
longueur de sonde

largeur (à mi-hauteur) de la fonction de pondération spatiale sélectionnant la région de l’espace qui

contribue au calcul de la vitesse du vent
Note 1 à l'article: La longueur de sonde est centrée sur la distance de mesure.
3.14
résolution en portée

variable liée au matériel décrivant le plus court intervalle de portée à partir duquel des informations de

signal indépendantes peuvent être obtenues
[SOURCE: ISO 28902-1:2012, 3.13]
© ISO 2018 – Tous droits réservés 3
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ISO 28902-3:2018(F)
3.15
fonction de pondération en portée

fonction de pondération de la vitesse radiale du vent le long de la ligne de visée

[SOURCE: ISO 28902-2:2017, 3.15]
3.16
résolution temporelle

variable liée au matériel décrivant le plus court intervalle de temps à partir duquel des informations de

signal indépendantes peuvent être obtenues
[SOURCE: ISO 28902-1:2012, 3.11]
3.17
biais de vitesse
écart systématique maximal dû à l’instrument lors du mesurage de la vitesse

Note 1 à l'article: Le biais de vitesse doit être réduit au minimum par un étalonnage adéquat, par exemple sur une

cible fixe.
[SOURCE: ISO 28902-2:2017, 3.17]
3.18
plage de vitesse

plage déterminée par la vitesse minimale mesurable du vent, la vitesse maximale mesurable du vent et

l’aptitude à mesurer le signe de la vitesse, sans ambiguïté

Note 1 à l'article: Selon l’application lidar, la plage de vitesse peut être définie en tant que vitesse radiale du vent

(lidar à balayage) ou en tant que vitesse horizontale du vent (profileur de vent).

[SOURCE: ISO 28902-2:2017, 3.18]
3.19
résolution en vitesse
écart-type instrumental de vitesse

Note 1 à l'article: La résolution en vitesse est déterminée par la largeur de tranche de traitement du signal.

3.20
cisaillement du vent
variation du vecteur vent dans un plan perpendiculaire à la direction du vent
[SOURCE: ISO 28902-2:2017, 3.20]
4 Principes essentiels du lidar Doppler hétérodyne
4.1 Présentation générale

Un lidar Doppler à ondes continues émet un faisceau laser étroit (voir Figure 1). Lorsqu’il se propage

dans l’atmosphère, le rayonnement laser est diffusé dans toutes les directions par les aérosols, les

molécules et autres particules diffusantes. Une partie du rayonnement diffusé revient vers le lidar;

elle est capturée par un télescope, détectée et analysée. Les aérosols et les molécules se déplaçant avec

l’atmosphère, il en résulte un décalage de fréquence par effet Doppler pour la lumière laser diffusée.

Aux longueurs d’onde (et donc fréquences) pertinentes pour un lidar Doppler hétérodyne (cohérent), la

majeure partie du rayonnement rétrodiffusé provient des aérosols.
4 © ISO 2018 – Tous droits réservés
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ISO 28902-3:2018(F)

L’analyse vise à déterminer la différence Δf entre la fréquence f de l’émission laser et la fréquence f de la

t r

lumière rétrodiffusée. Selon l’équation de Doppler, cette différence est proportionnelle à la composante

du vent sur la ligne de visée, comme indiqué dans la Formule (1):
Δ=ff −=fv−2/λ (1)
rt r
λ est la longueur d’onde du laser;

r est la composante du vent le long de la ligne de visée (composante du vecteur vent, v , le long

de l’axe du faisceau laser, considérée comme étant positive lorsque le vent souffle dans la

direction opposée au lidar).
Légende
1 particules diffusantes se déplaçant avec le vent
2 trajet optique du faisceau laser émis
3 axe optique du récepteur
4 instrument lidar
Figure 1 — Principe de mesure d’un lidar Doppler hétérodyne

Pour un système lidar Doppler à ondes continues, la distance de mesure est généralement réglée

en focalisant le faisceau pour lui donner une dimension minimale à la distance choisie. La lumière

rétrodiffusée à partir des régions situées à proximité du point de focalisation est efficacement ré-

imagée par le récepteur; la lumière provenant d’une région bien plus proche ou bien plus éloignée du

point de focalisation ou du foyer est mal captée.
© ISO 2018 – Tous droits réservés 5
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ISO 28902-3:2018(F)
4.2 Détection hétérodyne

Dans un lidar hétérodyne, la détection de la lumière captée par le télescope récepteur (à la fréquence

f = f + Δf) est décrite schématiquement à la Figure 2. La lumière reçue est mélangée au faisceau d’un

r t

laser continu très stable appelé oscillateur local (OL). La somme des deux ondes électromagnétiques –

rétrodiffusée et oscillateur local – est convertie en un signal électrique par un détecteur quadratique

(produisant un courant électrique proportionnel à la puissance de l’onde électromagnétique éclairant

sa surface sensible). Un filtre passe-haut analogique est ensuite appliqué pour éliminer les composantes

basse fréquence du signal et un filtre passe-bas est également appliqué pour éviter les problèmes causés

par un repliement spectral lors du traitement ultérieur du signal.
Légende
1 détecteur Circ'r circulateur
2 laser/oscillateur local (OL) w niveau du col du faisceau
3 réception de lumière Z longueur de Rayleigh
4 émission de lumière θ répartition angulaire totale
5 fibre monomodale w(z) fonction de la distance axiale
6 ouverture de l’émetteur/récepteur

7 profil gaussien du faisceau transmis et de BPLO («backpropagated local oscillator»)

Figure 2 — Principes de détection hétérodyne, illustrant un exemple d’architecture de lidar

à ondes continues et de géométrie de foyer

Le résultat est un courant i(t) de radiofréquence f + Δf – f , tel qu’indiqué dans la Formule (2) (dérivée

t lo
de la Formule (8) de la Référence [5]):
η⋅e
it =⋅22⋅⋅Ktξγ⋅ tP⋅ tP⋅⋅cos π Δ+ff − ft⋅+ϕ t +nt (2)
() () () () ()() (() ()
rlot lo
hf⋅
 
i t
het
t est le temps;
η est le rendement quantique du détecteur;
e est la charge électrique d’un électron;
h est la constante de Planck;

K est la constante instrumentale tenant compte des pertes de transmission dans le

récepteur;

ξ(t) est la modulation aléatoire de l’amplitude du signal par l’effet de chatoiement (voir 4.5.4);

6 © ISO 2018 – Tous droits réservés
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ISO 28902-3:2018(F)
γ(t) est le rendement hétérodyne;
P (t) est la puissance de la lumière rétrodiffusée;
P est la puissance de l’oscillateur local;
f est la fréquence de l’oscillateur local;
φ(t) est une phase aléatoire;
n(t) est le bruit blanc de détection;
i (t) est le signal hétérodyne.
het

Le rendement hétérodyne γ(t) est une mesure de la qualité du mélange optique des ondes rétrodiffusées

et de l’oscillateur local sur la surface du détecteur. Il ne peut pas dépasser 1. Un bon rendement

hétérodyne nécessite un dimensionnement et un alignement soigneux de l’oscillateur local par rapport

à l’onde rétrodiffusée. Les conditions optimales de mélange sont décrites dans la Référence [5]. Le

rendement hétérodyne n’est pas une fonction purement instrumentale; il dépend aussi de la turbulence

2 [6]

de l’indice de réfraction (Cn ) le long du faisceau laser . Dans des conditions de forte turbulence

atmosphérique, les fluctuations de l’indice de réfraction dégradent le rendement hétérodyne. Cela peut

se produire lorsque le lidar est utilisé à proximité du sol pendant une chaude journée d’été.

Pour un système cohérent à ondes continues, la puissance du signal optique moyennée dans le temps,

[7][8]

P , rétrodiffusée par les aérosols dans le récepteur est donnée avec une bonne approximation par

la Formule (3):
PP=ππβλ (3)

où P est la puissance transmise du laser et β(π) est le coefficient de rétrodiffusion atmosphérique en

1/(m·sr).

Il convient de souligner que P est indépendante de la distance de focalisation et de l’ouverture du

système. Cette approximation commence à se dégrader lorsque le système se rapproche de sa portée

opérationnelle maximale. Avec une valeur de 10 ·1/(m·sr) pour β(π) dans une couche limite d’air clair,

une puissance transmise P d’environ 1 W et λ d’environ 1,55 µm, la puissance reçue P qui en découle

T S

est de l’ordre de 50 fW. Ce chiffre souligne la nécessité d’une sensibilité extrêmement élevée du lidar.

Le rapport signal/bruit (SNR), pour un mesurage de vitesse de vent par un lidar cohérent à ondes

continues, est donné par la Formule (4):
SNR= (4)
Δ+vD1 vR+ v
()() ()

où η est un terme de rendement comprenant les pertes optiques et la sensibilité du photodétecteur (en

général η est égal à environ 0,5, n’approchant l’unité que pour un système «parfait»), P est la puissance

−19

du signal d’entrée et (hc/λ) est l’énergie quantique de la lumière, de l’ordre de 1,3·10 J à une longueur

d’onde de 1,55 µm. La bande passante du signal Δv est déterminée par trois contributions (largeur

instrumentale, élargissement spectral par le temps de transfert et par la turbulence), et le terme entre

parenthèses désigne les diverses sources de bruit. D(v) et R(v) représentent respectivement la densité

spectrale de puissance (à la fréquence v) du b
...