ASTM E1791-96(2014)

Standard Practice for Transfer Standards for Reflectance Factor for Near-Infrared Instruments Using Hemispherical Geometry

SIGNIFICANCE AND USE
5.1 Most commercial reflectometers and spectrophotometers with reflectance capability measure relative reflectance. The instrument reading is the ratio of the measured radiation reflected from the reference specimen to the measured radiation reflected by the test specimen. That ratio is dependent on specific instrument parameters.  
5.2 National standardizing laboratories and some research laboratories measure reflectance on instruments calibrated from basic principles, thereby establishing a scale of absolute reflectance as described in CIE Publication No. 44 (5). These measurements are sufficiently difficult and of prohibitive cost that they are usually left to laboratories that specialize in them.  
5.3 A standard that has been measured on an absolute scale could be used to transfer that scale to a reflectometer. While such procedures exist, the constraints placed on the mechanical properties restrict the suitability of some of the optical properties, especially those properties related to the geometric distribution of reflected radiation. Thus, reflectance factor standards that are sufficiently rugged or cleanable to use as permanent transfer standards, with the exception of the sintered PTFE standards, depart considerably from the perfect diffuser in the geometric distribution of reflected radiation.  
5.4 The geometric distribution of reflected radiance from such standards is sufficiently diffuse that such a standard can provide a dependable calibration of a directional-hemispherical or certain directional-directional reflectometers. Although pressed powder standards are subject to contamination and breakage, the reflectance factor of pressed powder can be sufficiently reproducible from specimen to specimen from a given lot of powder to allow the assignment of absolute reflectance factor values to all of the powder in a lot.  
5.5 Sintered PTFE materials exhibit sufficient reproducibility from within the same specimen after resurfacing or cleaning the spec...
SCOPE
1.1 This practice covers procedures for the preparation and use of acceptable transfer standards for NIR spectrophotometers. Procedures for calibrating the reflectance factor of materials on an absolute basis are contained in CIE Publication No. 44 (9). Both the pressed powder samples and the sintered PTFE materials are used as transfer standards for such calibrations because they have very stable reflectance factors that are nearly constant with wavelength and because the distribution of flux resembles closely that from the perfect reflecting diffuser.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 30-Apr-2014
• ICS: 37.020 - Optical equipment
• Technical Committee: E13 - Molecular Spectroscopy and Separation Science
• Drafting Committee: E13.03 - Infrared and Near Infrared Spectroscopy

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:E1791 −96 (Reapproved 2014)
Standard Practice for
Transfer Standards for Reflectance Factor for Near-Infrared
Instruments Using Hemispherical Geometry
This standard is issued under the fixed designation E1791; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The internationally accepted standard of reflectance is the perfect reflecting diffuser. This ideal
reflectingsurfacereflects100%oftheradiantpowerincidentonit,suchthattheradianceisthesame
foralldirectionswithinthehemisphereofsolidangles.Nophysicalrealizationofthisstandardexists.
Optical properties of standards prepared from pressed plaques of barium sulfate (BaSO)or
polytetrafluoroethylene (PTFE), as well as commercially available samples of sintered PTFE (1-4),
canapproximatethoseofawhitematerial.Forfurtherinformation,seeCommissionInternationalede
L’Eclairage (CIE) Publication No. 46 (5).Additional transfer standards are required that have a very
stable reflectance factor that is constant with wavelength and that have a range of values from near
zero to close to that of the perfect reflecting diffuser. Such materials as carbon-black doped sintered
PTFE (6-8) fulfill this requirement. The principle uses of a reflectance factor standard are for
transferring an absolute scale of reflectance to a more durable material or for calibrating near-infrared
(NIR) spectrophotometers for linearity of reflectance scale. In theory, this transfer, conducted from
first principles, should be quite easy. In practice, values are likely to be required for parameters that
are unknown, proprietary, or require a highly sophisticated level of skill. Some, but not all, of these
parameters are discussed in this practice.
1. Scope responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 This practice covers procedures for the preparation and
bility of regulatory limitations prior to use.
use of acceptable transfer standards for NIR spectrophotom-
eters. Procedures for calibrating the reflectance factor of
2. Referenced Documents
materialsonanabsolutebasisarecontainedinCIEPublication
2.1 ASTM Standards:
No. 44 (9). Both the pressed powder samples and the sintered
E131Terminology Relating to Molecular Spectroscopy
PTFE materials are used as transfer standards for such calibra-
E259Practice for Preparation of Pressed Powder White
tions because they have very stable reflectance factors that are
Reflectance Factor Transfer Standards for Hemispherical
nearly constant with wavelength and because the distribution
and Bi-Directional Geometries
of flux resembles closely that from the perfect reflecting
E284Terminology of Appearance
diffuser.
1.2 The values stated in SI units are to be regarded as
3. Terminology
standard. No other units of measurement are included in this
3.1 Definitions—Terms and definitions in Terminology
standard.
E284 are applicable to this practice.
1.3 This standard does not purport to address all of the
3.2 Descriptions of Terms Specific to This Standard—The
safety concerns, if any, associated with its use. It is the
followingdefinitionsareparticularlyimportanttothispractice.
3.2.1 linearity—the ability of a photometric system to yield
This practice is under the jurisdiction ofASTM Committee E13 on Molecular
a linear relationship between the radiant power incident on its
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
mittee E13.03 on Infrared and Near Infrared Spectroscopy.
Current edition approved May 1, 2014. Published June 2014. Originally
ϵ1
approved in 1996. Last previous edition approved in 2008 as E1791–96(2008) . For referenced ASTM standards, visit the ASTM website, www.astm.org, or
DOI: 10.1520/E1791-96R14. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof Standards volume information, refer to the standard’s Document Summary page on
this practice. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1791−96 (2014)
TABLE 2 6°/Typical Diffuse Reflectance for Three Sintered
detectorandsomemeasurablequantityprovidedbythesystem.
Carbon-Black Doped PTFE
(E131)
Wavelength, nm 80 % Standard 10 % Standard 2 % Standard
3.2.2 near-infrared, adj—the region of the electromagnetic
250 0.774 0.106 0.015
spectrum for radiation of wavelengths between 780 and 2500
300 0.793 0.099 0.016
nm (0.78 and 2.50 µm).
400 0.795 0.097 0.017
500 0.796 0.099 0.017
3.2.3 perfect reflecting diffuser—idealreflectingsurfacethat
600 0.797 0.101 0.017
neither absorbs nor transmits light, but reflects diffusely, with
700 0.799 0.103 0.017
800 0.802 0.105 0.018
the radiance of the reflecting surface being the same for all
900 0.803 0.105 0.017
reflecting angles, regardless of the angular distribution of the
1000 0.805 0.106 0.018
incident light. 1100 0.806 0.108 0.017
1200 0.807 0.109 0.018
3.2.4 reflectance, r, n—ratio of the reflected radiant or
1300 0.808 0.111 0.018
1400 0.808 0.112 0.018
luminous flux to the incident flux in the given conditions (1).
1500 0.810 0.113 0.020
3.2.4.1 The term reflectance is often used in a general sense
1600 0.811 0.114 0.021
or as an abbreviation for reflectance factor. Such usage may be
1700 0.812 0.115 0.023
1800 0.813 0.116 0.024
assumed unless the definition is specifically required by the
1900 0.811 0.118 0.026
context.
2000 0.814 0.117 0.027
3.2.5 reflectance factor, R, n—ratioofthefluxreflectedfrom
2100 0.809 0.114 0.030
2200 0.812 0.110 0.032
the specimen to the flux reflected from the perfect reflecting
2300 0.813 0.110 0.035
diffuser under the same geometric and spectral conditions of
2400 0.809 0.103 0.034
measurement (2).
2500 0.809 0.101 0.038
thickness#7 mm thickness#5 mm thickness#3mm
4. Summary of Practice
4.1 Procedures for the preparation of packed powder
samples of barium sulfate and PTFE can be found in Practice
bance features and may be used to transfer a scale of linearity
E259. Sintered PTFE samples are commercially available.
in reflectance factor to another material or instrument.
Reflectance data for this material are given in Table 1. These
materials provide close approximation to the optical properties
5. Significance and Use
of the perfect reflecting diffuser and may be used to transfer a
5.1 Most commercial reflectometers and spectrophotom-
scale of reflectance factor to another material or instrument.
eters with reflectance capability measure relative reflectance.
4.2 Sintered carbon-black doped PTFE samples are also
The instrument reading is the ratio of the measured radiation
commercially available and are described in Table 2. These
reflected from the reference specimen to the measured radia-
materials provide close approximation to the optical properties
tion reflected by the test specimen. That ratio is dependent on
of a perfect reflecting diffuser with spectrally neutral absor-
specific instrument parameters.
5.2 National standardizing laboratories and some research
laboratories measure reflectance on instruments calibrated
TABLE 1 6°/Typical Diffuse Reflectance for Sintered PTFE
from basic principles, thereby establishing a scale of absolute
Wavelength, nm Reflectance Factor reflectance as described in CIE Publication No. 44 (5). These
250 0.940 measurements are sufficiently difficult and of prohibitive cost
300 0.977
thattheyareusuallylefttolaboratoriesthatspecializeinthem.
400 0.991
500 0.991
5.3 Astandard that has been measured on an absolute scale
600 0.991
could be used to transfer that scale to a reflectometer. While
700 0.990
suchproceduresexist,theconstraintsplacedonthemechanical
800 0.991
900 0.991
properties restrict the suitability of some of the optical
1000 0.990
properties, especially those properties related to the geometric
1100 0.990
distribution of reflected radiation. Thus, reflectance factor
1200 0.989
1300 0.988
standards that are sufficiently rugged or cleanable to use as
1400 0.986
permanenttransferstandards,withtheexceptionofthesintered
1500 0.988
PTFE standards,
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: E1791 − 96 (Reapproved 2008) E1791 − 96 (Reapproved 2014)
Standard Practice for
Transfer Standards for Reflectance Factor for Near-Infrared
Instruments Using Hemispherical Geometry
This standard is issued under the fixed designation E1791; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Trademark names removed editorially in April 2008.
INTRODUCTION
The internationally accepted standard of reflectance is the perfect reflecting diffuser. This ideal
reflecting surface reflects 100 % of the radiant power incident on it, such that the radiance is the same
for all directions within the hemisphere of solid angles. No physical realization of this standard exists.
Optical properties of standards prepared from pressed plaques of barium sulfate (BaSO ) or
polytetrafluoroethylene (PTFE), as well as commercially available samples of sintered PTFE (1-4),
can approximate those of a white material. For further information, see Commission Internationale de
L’Eclairage (CIE) Publication No. 46 (5). Additional transfer standards are required that have a very
stable reflectance factor that is constant with wavelength and that have a range of values from near
zero to close to that of the perfect reflecting diffuser. Such materials as carbon-black doped sintered
PTFE (6-8) fulfill this requirement. The principle uses of a reflectance factor standard are for
transferring an absolute scale of reflectance to a more durable material or for calibrating near-infrared
(NIR) spectrophotometers for linearity of reflectance scale. In theory, this transfer, conducted from
first principles, should be quite easy. In practice, values are likely to be required for parameters that
are unknown, proprietary, or require a highly sophisticated level of skill. Some, but not all, of these
parameters are discussed in this practice.
1. Scope
1.1 This practice covers procedures for the preparation and use of acceptable transfer standards for NIR spectrophotometers.
Procedures for calibrating the reflectance factor of materials on an absolute basis are contained in CIE Publication No. 44 (9). Both
the pressed powder samples and the sintered PTFE materials are used as transfer standards for such calibrations because they have
very stable reflectance factors that are nearly constant with wavelength and because the distribution of flux resembles closely that
from the perfect reflecting diffuser.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
E131 Terminology Relating to Molecular Spectroscopy
This practice is under the jurisdiction of ASTM Committee E13 on Molecular Spectroscopy and Separation Science and is the direct responsibility of Subcommittee
E13.03 on Infrared and Near Infrared Spectroscopy.
Current edition approved March 15, 2008May 1, 2014. Published April 2008June 2014. Originally approved in 1996. Last previous edition approved in 20002008 as
ϵ1
E1791 – 96 (2000).(2008) . DOI: 10.1520/E1791-96R08E01.10.1520/E1791-96R14.
The boldface numbers in parentheses refer to the list of references at the end of this practice.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1791 − 96 (2014)
E259 Practice for Preparation of Pressed Powder White Reflectance Factor Transfer Standards for Hemispherical and
Bi-Directional Geometries
E284 Terminology of Appearance
3. Terminology
3.1 Definitions—Terms and definitions in Terminology E284 are applicable to this practice.
3.2 Descriptions of Terms Specific to This Standard—The following definitions are particularly important to this practice.
3.2.1 linearity—the ability of a photometric system to yield a linear relationship between the radiant power incident on its
detector and some measurable quantity provided by the system. (E131)
3.2.2 near-infrared, adj—the region of the electromagnetic spectrum for radiation of wavelengths between 780 and 2500 nm
(0.78 and 2.50 μm).
3.2.3 perfect reflecting diffuser—ideal reflecting surface that neither absorbs nor transmits light, but reflects diffusely, with the
radiance of the reflecting surface being the same for all reflecting angles, regardless of the angular distribution of the incident light.
3.2.4 reflectance, r, n—ratio of the reflected radiant or luminous flux to the incident flux in the given conditions (1).
3.2.4.1 The term reflectance is often used in a general sense or as an abbreviation for reflectance factor. Such usage may be
assumed unless the definition is specifically required by the context.
3.2.5 reflectance factor, R, n—ratio of the flux reflected from the specimen to the flux reflected from the perfect reflecting
diffuser under the same geometric and spectral conditions of measurement (2).
4. Summary of Practice
4.1 Procedures for the preparation of packed powder samples of barium sulfate and PTFE can be found in Practice E259.
Sintered PTFE samples are commercially available. Reflectance data for this material are given in Table 1. These materials provide
close approximation to the optical properties of the perfect reflecting diffuser and may be used to transfer a scale of reflectance
factor to another material or instrument.
4.2 Sintered carbon-black doped PTFE samples are also commercially available and are described in Table 2. These materials
provide close approximation to the optical properties of a perfect reflecting diffuser with spectrally neutral absorbance features and
may be used to transfer a scale of linearity in reflectance factor to another material or instrument.
5. Significance and Use
5.1 Most commercial reflectometers and spectrophotometers with reflectance capability measure relative reflectance. The
instrument reading is the ratio of the measured radiation reflected from the reference specimen to the measured radiation reflected
by the test specimen. That ratio is dependent on specific instrument parameters.
TABLE 1 6°/Typical Diffuse Reflectance for Sintered PTFE
Wavelength, nm Reflectance Factor
250 0.940
300 0.977
400 0.991
500 0.991
600 0.991
700 0.990
800 0.991
900 0.991
1000 0.990
1100 0.990
1200 0.989
1300 0.988
1400 0.986
1500 0.988
1600 0.987
1700 0.984
1800 0.984
1900 0.978
2000 0.970
2100 0.950
2200 0.963
2300 0.955
2400 0.944
2500 0.940
Density = 1500 kg/m ; thickness $7 mm
E1791 − 96 (2014)
TABLE 2 6°/Typical Diffuse Reflectance for Three Sintered
Carbon-Black Doped PTFE
Wavelength, nm 80 % Standard 10 % Standard 2 % Standard
250 0.774 0.106 0.015
300 0.793 0.099 0.016
400 0.795 0.097 0.017
500 0.796 0.099 0.017
600 0.797 0.101 0.017
700 0.799 0.103 0.017
800 0.802 0.105 0.018
900 0.803 0.105 0.017
1000 0.805 0.106 0.018
1100 0.806 0.108 0.017
1200 0.807 0.109 0.018
1300 0.808 0.111 0.018
1400 0.808 0.112 0.018
1500 0.810 0.113 0.020
1600 0.811 0.114 0.021
1700 0.812 0.115 0.023
1800 0.813 0.116 0.024
1900 0.811 0.118 0.026
2000 0.814 0.117 0.027
2100 0.809 0.114 0.030
2200 0.812 0.110 0.032
2300 0.813 0.110 0.035
2400 0.809 0.103 0.034
2500 0.809 0.101 0.038
thickness #7 mm thickness #5 mm thickness #3 mm
5.2 National standardizing laboratories and some research laboratories measure reflectance on instruments calibrated from basic
principles, thereby establishing a scale of absolute reflectance as described in CIE Publication No. 44 (5). These measurements are
sufficiently difficult and of prohibitive cost that they are usually left to laboratories that specialize in them.
5.3 A standard that has been measured on an
...