Characterization of pavement texture by use of surface profiles — Part 6: Verification of the performance of laser profilometers used for pavement texture measurements

This document describes methods for checking laser profilometer performance with respect to the capability of such equipment in measuring pavement texture. The objective of this document is to make available an internationally accepted procedure by which performance of various laser-based equipment for pavement texture measurements can be evaluated. The document includes guidelines and recommendations intended to assist users of laser profilometers in verification of their equipment. This document is not intended as the basis for qualifying or approving laser profilometers. The procedure aims at providing tools for verifying that such systems perform satisfactory in all respects important for the correct measurements of texture, as well as to detect when and in what way the performance is unsatisfactory. This document also provides some general information about the limitations and trade-offs of laser profilometer systems. Modern profilometers in use for measurements on pavements are almost entirely of the contactless type (such as laser point or line triangulation) designed for two- or three-dimensional measurements, and this document is intended for evaluating the performance of this type of profilometers. However, some other contactless types of profilometer can use applicable parts of ISO 13473. This document has been prepared as a result of a need identified to correct for unacceptable differences in results measured by various equipment, even if the operators of these claim that they meet the applicable part of ISO 13473. It is not intended for other applications than pavement texture measurement. To be able to exclude errors influenced by programming mistakes or wrong interpretation of ISO 13473‑1 a reference program code, digital profiles and calculated reference MPD-values can be reached via Annex A. This document is a complement to other parts of ISO 13473 in which some specifications are given but methods to check them are not included.

Caractérisation de la texture d'un revêtement de chaussée à partir de relevés de profils de la surface — Partie 6: Vérification de la performance des profilomètres lasers utilisés pour les mesurages de la texture d'un revêtement

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Published
Publication Date
01-Nov-2021
Current Stage
6060 - International Standard published
Start Date
02-Nov-2021
Due Date
05-Nov-2021
Completion Date
02-Nov-2021
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PUBLICLY ISO/PAS
AVAILABLE 13473-6
SPECIFICATION
First edition
2021-11
Characterization of pavement texture
by use of surface profiles —
Part 6:
Verification of the performance of
laser profilometers used for pavement
texture measurements
Caractérisation de la texture d'un revêtement de chaussée à partir de
relevés de profils de la surface —
Partie 6: Vérification de la performance des profilomètres lasers
utilisés pour les mesurages de la texture d'un revêtement
Reference number
ISO/PAS 13473-6:2021(E)
© ISO 2021

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ISO/PAS 13473-6:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
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
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Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
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ISO/PAS 13473-6:2021(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms.2
5 Methodology and its use . 3
6 Identification and evaluation of design and performance parameters .3
7 Test methods and instruments .4
7.1 General conditions . 4
7.2 Laser power . 4
7.2.1 Test method . 4
7.2.2 Instruments . 4
7.3 Laser spot size . 5
7.3.1 Test method . 5
7.3.2 Instruments . 5
7.4 Accuracy of the calibration (scale) factor . 5
7.4.1 General . 5
7.4.2 Method and instruments . 6
7.5 Nonlinearity . 6
7.5.1 General . 6
7.5.2 Test method . 6
7.5.3 Instruments . 6
7.6 Background noise. 6
7.6.1 Method . . 6
7.6.2 Evaluation of the result . 7
7.7 Horizontal position measurement accuracy . 7
7.7.1 Test method for mobile (continuous) systems . 7
7.7.2 Test method for stationary (spot) systems . 7
7.8 Sensitivity to abrupt change in surface reflectivity . 7
7.8.1 Method . . 7
7.8.2 Instruments . 8
7.9 Spike content of measured signal . 8
7.10 Effect of ambient light . 8
7.10.1 Method . . 8
7.10.2 Instruments . 8
7.11 Dropout rate. 9
7.11.1 Method . . 9
7.11.2 Instruments . 9
7.12 Validation of dropout detection system . 9
7.12.1 Method . . 9
7.12.2 Instruments . 10
7.13 Synchronization between invalid parts of the profile and dropout indications . 10
7.13.1 Method . . 10
7.13.2 Instruments . 10
8 Ambient testing conditions .11
9 Frequency of testing . .11
10 Test report .11
Annex A (informative) Testing the calculation procedure (software) .13
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ISO/PAS 13473-6:2021(E)
Bibliography .14
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ISO/PAS 13473-6:2021(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 43, Acoustics, Subcommittee SC 1, Noise.
A list of all parts in the ISO 13473 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/PAS 13473-6:2021(E)
Introduction
Pavement texture data are often used in research and surveys of pavement surface properties, such
as tyre/road noise, rolling resistance, skid resistance, as well as splash and spray. Measurements of
pavement texture are used in several other ISO standards; mostly to characterize test or reference
surfaces.
For the measurement of pavement surface texture, laser profilometers are most frequently used. In
recent years, it has appeared that, despite the use of standard methods (such as those in other parts
of ISO 13473), there can be differences between results measured by various equipment, exceeding
normal uncertainty estimations. One of the reasons for this can be that the equipment does not fully
[3]
meet the intentions of the standards; for example ISO 13473-3 .
To deal with this problem, this document specifies how one can verify that a particular device meets
the intended characteristics of laser profilometer systems used for pavement texture measurements.
WARNING — Emitted laser beams could be hazardous for the eye and all tests done according to this
standard shall be done with the appropriate safety precautions for the specific sensor.
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PUBLICLY AVAILABLE SPECIFICATION ISO/PAS 13473-6:2021(E)
Characterization of pavement texture by use of surface
profiles —
Part 6:
Verification of the performance of laser profilometers used
for pavement texture measurements
1 Scope
This document describes methods for checking laser profilometer performance with respect to the
capability of such equipment in measuring pavement texture.
The objective of this document is to make available an internationally accepted procedure by which
performance of various laser-based equipment for pavement texture measurements can be evaluated.
The document includes guidelines and recommendations intended to assist users of laser profilometers
in verification of their equipment. This document is not intended as the basis for qualifying or approving
laser profilometers. The procedure aims at providing tools for verifying that such systems perform
satisfactory in all respects important for the correct measurements of texture, as well as to detect
when and in what way the performance is unsatisfactory. This document also provides some general
information about the limitations and trade-offs of laser profilometer systems.
Modern profilometers in use for measurements on pavements are almost entirely of the contactless
type (such as laser point or line triangulation) designed for two- or three-dimensional measurements,
and this document is intended for evaluating the performance of this type of profilometers. However,
some other contactless types of profilometer can use applicable parts of ISO 13473.
This document has been prepared as a result of a need identified to correct for unacceptable
differences in results measured by various equipment, even if the operators of these claim that
they meet the applicable part of ISO 13473. It is not intended for other applications than pavement
texture measurement. To be able to exclude errors influenced by programming mistakes or wrong
interpretation of ISO 13473-1 a reference program code, digital profiles and calculated reference MPD-
values can be reached via Annex A. This document is a complement to other parts of ISO 13473 in which
some specifications are given but methods to check them are not included.
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.
ISO 13473-1, Characterization of pavement texture by use of surface profiles — Part 1: Determination of
mean profile depth
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13473-1 and the following
apply.
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
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ISO/PAS 13473-6:2021(E)
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
laser profilometer
equipment for contactless pavement texture measurement using a laser spot or line projected on the
surface captured by a device that accurately digitizes and records texture profiles when the system is
moved over the pavement surface
3.2
background noise
variation of the signal when the measurement system is at rest
Note 1 to entry: Such noise often is of the type that is called white noise.
3.3
measurement range
range of values of vertical distance covered by the sensor,
Note 1 to entry: See Figure 1.
3.4
standoff
distance between middle of the measurement range (3.3) and pavement
Note 1 to entry: See Figure 1.
Key
1 sensor
a
Standoff.
b
Measurement range.
Figure 1 — Illustration of the terms measurement range and standoff
4 Symbols and abbreviated terms
A list of symbols and abbreviations used in this document is given in Table 1.
Table 1 — The meaning of symbols and abbreviations
Reference docu- Meaning
Symbol or term
ment
DAC EN 13108-1 Dense Asphalt Concrete (pavement)
MPD ISO 13473-1 Mean Profile Depth
MSD ISO 13473-1 Mean Segment Depth
PA EN 13108-7 Porous Asphalt (pavement)
RMS ISO 13473-1 Root Mean Square
SMA EN 13108-5 Stone Mastic Asphalt (pavement)
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ISO/PAS 13473-6:2021(E)
5 Methodology and its use
The important technical characteristics of laser profilometers used for measurements of pavement
texture are identified, and for each one a procedure is proposed that intends to check that particular
performance of the device and, where appropriate, compare it with limits for acceptable performance.
When a device or system has been checked according to this document, it is possible to refer to this
document and claim to what extent the device meets the given requirements.
6 Identification and evaluation of design and performance parameters
This clause identifies design and performance parameters that are of interest in the subject of pavement
texture measurements by laser profilometers. Some of the parameters are subject to evaluation in this
document, while others are left to the manufacturers’ own specifications.
The following fundamental design parameters are not intended to be evaluated according to this
specification, but it should be checked that they are all listed in a specification by the manufacturer. The
items considered include:
— operating temperature range;
— standoff;
— triangulation angles;
— laser light wavelength;
— sampling frequency;
— existence of antialiasing filter;
— horizontal resolution in longitudinal direction (usually determined by the setting of an encoder);
— horizontal resolution in transversal direction (in 3D equipment, usually determined by the number
of points sampled across the laser line);
— vertical resolution;
— vertical measurement range.
The results are important for the user and are provided as information; no judgement of conformity to
requirements is made for these parameters.
The following parameters are intended to be evaluated according to this specification:
a) laser power;
b) laser spot size;
c) calibration (scale) factor;
d) linearity;
e) background noise;
f) horizontal position measurement accuracy;
g) sensitivity to abrupt change in surface reflectivity;
h) spike content of measured signal;
i) effect of ambient light;
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ISO/PAS 13473-6:2021(E)
j) dropout rate;
k) validation of dropout detection system;
l) synchronization between invalid parts of the profile and dropout indications.
7 Test methods and instruments
7.1 General conditions
The following subclauses suggest test methods to be used, while Clause 9 suggests the frequency of
testing.
If the equipment can operate at different modes optimized for certain pavements (such as on bright or
dark surfaces), the tests described below should be performed in the modes which are relevant for the
intended pavements.
When performing the following tests, where relevant, the laser system shall be mounted at an angle
typical of its normal operation.
All tests described in this clause can be done with both spot and line lasers. Regarding line lasers, all
tests should be done at the part of the line that is used to measure the texture properties.
7.2 Laser power
7.2.1 Test method
The power of a spot laser should be measured and integrated over the entire laser spot. The spot should
be measured in a position located at standoff. The physical design of receivers (laser power sensors)
for laser power meters are not adapted for measuring the power of a laser line at standoff. Instead, it
is recommended to use a receiver with a large area and measure the power of a line laser as close as
possible to emitted laser source.
Follow the recommendations from the supplier to decide a limit of approval for the laser power.
[6]
It is recommended to apply ISO 13694 for this purpose.
NOTE 1 In order to monitor the progress of laser deterioration with time, measure this power when the sensor
is new and then periodically monitor how the laser diode deteriorates. The period depends on the type of laser
and the use of the laser, but if the laser is in operation frequently or during long periods over a year, a suitable
period would be a test every year. If the measured laser power is less than half of the initially measured laser
power this is an indication why the performance in the other tests can be insufficient.
NOTE 2 Loss of laser power might, for example, have the effect of increasing background noise and the rate of
drop-outs.
NOTE 3 When measuring the laser power, search for the maximum power by moving the receiver of the laser
power meter and register the value.
7.2.2 Instruments
There are commonly used instruments to measure laser power, which integrate over the entire area,
including the appropriate laser wavelength, and give the total time-averaged power. It is up to the user
to find such an instrument.
NOTE Use the same type of instrument to follow the deterioration of the laser power since different
instruments tend to give different results.
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ISO/PAS 13473-6:2021(E)
7.3 Laser spot size
7.3.1 Test method
Check the vertical measurement range of the sensor, according to the manufacturer’s specifications.
Measure laser spot size at standoff and near the two ends of the range (at 10 % and 90 % of the vertical
range).
For spot lasers:
The effective spot is taken as that contained within an area limited by a contour line where the intensity
of the spot is 1/e (approximately 37 %) of the maximum intensity within the spot. The laser spot size is
the maximum diameter of the spot within this contour line; see Figure 2.
NOTE The maximum laser spot size is the diameter indicated by a straight line in the figure.
Figure 2 — Example of enlarged laser spot, where light intensity is indicated by colour (dark
red is the highest and dark blue is the weakest)
For line lasers:
A line laser’s effective line width is taken as that contained within a distance limited by where the
intensity of the line width is 1/e (approximately 37 %) of the maximum intensity.
Regarding the required maximum laser spot size, refer to the appropriate standard; for example
[5] [3]
ISO 13473-1 for MPD and ISO 13473-5 for megatexture measurements, and also to ISO 13473-3 for
various classes of profilometers.
[2]
It is recommended to consider the method in ISO 11146-1 for this purpose.
NOTE For 3D equipment using a continuous line, the size of the line is determined in the direction
perpendicular to the line.
7.3.2 Instruments
Use a laser beam analyser or any other system designated for the purpose of measuring laser spot sizes.
NOTE It is possible to make this kind of measurement by using a razorblade to shade off part of the
illuminated spot and moving this in the laser spot plane by a micrometer screw. See Reference [10] for hints and
instructions.
7.4 Accuracy of the calibration (scale) factor
7.4.1 General
Each sensor is normally delivered with a “scale factor”; i.e. how to convert the output values of the sensor
to a displacement in millimetres. Alternatively, the output is presented directly as a displacement or
position in millimetres. The accuracy of this should be checked.
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ISO/PAS 13473-6:2021(E)
7.4.2 Method and instruments
One of many ways of performing this test is to use the table of a metal workshop milling machine, the
vertical position of which can be moved with very high precision and resolution (tolerance ±10 μm).
The laser sensor is mounted firmly above the table at a height appropriate with respect to the standoff.
Then the output of the sensor is observed when the table is in a lower position and in a higher position;
at a height difference equal to a major fraction of the vertical measurement range (not outside 10% to
90 % of the range). The scale factor is expressed in mm per output unit.
Another way is to make a measurement of a step in vertical displacement from a lower to an upper
surface; by putting a gauge block, with a known and very precise thickness (tolerance ±10 μm), on
top of another block under the laser spot or line; thick enough to cover a major fraction of the vertical
measurement range. It is preferred that this measurement is static, and one shall make sure that there
is no effect of a slope of these surfaces or of the mounting of the sensor. Limits of approval depends on
the application of the measurement and can be found in ISO 13473-3.
7.5 Nonlinearity
7.5.1 General
A line laser is checked at the part of the laser line used to measure texture while the spot laser obviously
is checked where the spot is.
7.5.2 Test method
This parameter is easily checked by extending the calibration procedure using gauge blocks, by putting
gauge blocks on top of each other to cover the measurement range, with each step being 1/5 or less of the
measurement range. Make this test within 10 % and 90 % of the measurement range. The measurement
time on each step should be enough to reduce noise influence and reach a stable signal. For example,
the output signal can then be plotted against the height of the steps, and one may calculate how much
each point deviates from a perfect 1:1 relation. The maximum non-linearity should be reported as a
percentage of the full range. Limits of approval depends on the application of the measurement and can
be found in ISO 13473-3.
7.5.3 Instruments
Use gauge blocks as mentioned above. Another possibility is to produce a very accurate metal block with
steps of known height (tolerance ±10 μm) and make a profile recording of this object. A third option is
to use a table of a metal workshop milling machine, the vertical position of which can be moved with
very high precision and resolution (tolerance ±10 μm) and moving the table vertically in certain regular
steps.
7.6 Background noise
7.6.1 Method
For 2D systems, a useful method is to operate the device over a matte white paper at standstill and
measure the output of the sensor when the sensor is triggered in a way which is typical of its operation
on pavement surfaces. This includes a common simulated operating speed. For mobile measurements on
road surfaces a normal speed may be 20 m/s (72 km/h). A duration of the measurement corresponding
to an equivalent distance of 100 m is recommended.
General option: Measure the RMS value of the output signal, calculated in millimetres.
MPD option: For devices measuring/calculating MPD, calculate the MPD in millimetres for this signal,
pretending that the device is operating on a perfectly smooth pavement surface and at an appropriate
speed. In this case, the spike removal procedure should be
...

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