1、Designation: E 1791 96 (Reapproved 2000)Standard Practice forTransfer Standards for Reflectance Factor for Near-InfraredInstruments Using Hemispherical Geometry1This standard is issued under the fixed designation E 1791; the number immediately following the designation indicates the year oforiginal
2、adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONThe internationally accepted standard of reflectance is the perfect
3、 reflecting diffuser. This idealreflecting surface reflects 100 % of the radiant power incident on it, such that the radiance is the samefor all directions within the hemisphere of solid angles. No physical realization of this standard exists.Optical properties of standards prepared from pressed pla
4、ques of barium sulfate (BaSO4)orpolytetrafluoroethylene (PTFE), as well as commercially available samples of sintered PTFE (1-4),2can approximate those of a white material. For further information, see CIE Publication No. 46 (5) andSpecification D 1457. Additional transfer standards are required tha
5、t have a very stable reflectancefactor that is constant with wavelength and that have a range of values from near zero to close to thatof the perfect reflecting diffuser. Such materials as carbon-black doped sintered PTFE (6-8) fulfill thisrequirement. The principle uses of a reflectance factor stan
6、dard are for transfering an absolute scaleof reflectance to a more durable material or for calibrating near-infrared (NIR) spectrophotometers forlinearity of reflectance scale. In theory, this transfer, conducted from first principles, should be quiteeasy. In practice, values are likely to be requir
7、ed for parameters that are unknown, proprietary, orrequire a highly sophisticated level of skill. Some, but not all, of these parameters are discussed in thispractice.1. Scope1.1 This practice covers procedures for the preparation anduse of acceptable transfer standards for NIR spectrophotom-eters.
8、Procedures for calibrating the reflectance factor ofmaterials on an absolute basis are contained in CIE PublicationNo. 44 (9). Both the pressed powder samples and the sinteredPTFE materials are used as transfer standards for such calibra-tions because they have very stable reflectance factors that a
9、renearly constant with wavelength and because the distributionof flux resembles closely that from the perfect reflectingdiffuser.1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address
10、all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 1457 Specificatio
11、n for Polytetrafluoroethylene (PTFE)Molding and Extrusion Materials3E 131 Terminology Relating to Molecular Spectroscopy4E 259 Practice for Preparation of Pressed Powder WhiteReflectance Factor Transfer Standards for HemisphericalGeometry5E 284 Terminology of Appearance53. Terminology3.1 Definitions
12、Terms and definitions in TerminologyE 284 are applicable to this practice.3.2 Descriptions of Terms Specific to This StandardThefollowing definitions are particularly important to this practice.3.2.1 linearitythe ability of a photometric system to yielda linear relationship between the radiant power
13、 incident on itsdetector and some measureable quantity provided by thesystem. (E 131)3.2.2 near-infrared, adjthe region of the electromagneticspectrum for radiation of wavelengths between 780 and 2500nm (0.78 and 2.50 m).1This practice is under the jurisdiction of ASTM Committee E-13 on MolecularSpe
14、ctroscopy and is the direct responsibility of Subcommittee E13.11 on Chemo-metrics.Current edition approved March 10, 1996. Published May 1996.2The boldface numbers in parentheses refer to the list of references at the end ofthis practice.3Annual Book of ASTM Standards, Vol 08.01.4Annual Book of AST
15、M Standards, Vol 03.06.5Annual Book of ASTM Standards, Vol 06.01.1Copyright ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.3.2.3 perfect reflecting diffuserideal reflecting surface thatneither absorbs nor transmits light, but reflects diffusely,with the radiance of the
16、reflecting surface being the same for allreflecting angles, regardless of the angular distribution of theincident light.3.2.4 reflectance, r, nratio of the reflected radiant orluminous flux to the incident flux in the given conditions (1).3.2.4.1 The term reflectance is often used in a general sense
17、or as an abbreviation for reflectance factor. Such usage may beassumed unless the definition is specifically required by thecontext.3.2.5 reflectance factor, R, nratio of the flux reflectedfrom the specimen to the flux reflected from the perfectreflecting diffuser under the same geometric and spectr
18、alconditions of measurement (2).4. Summary of Practice4.1 Procedures for the preparation of packed powdersamples of barium sulfate and PTFE can be found in PracticeE 259. Sintered PTFE samples are commercially available.6Reflectance data for this material are given in Table 1. Thesematerials provide
19、 close approximation to the optical propertiesof the perfect reflecting diffuser and may be used to transfer ascale of reflectance factor to another material or instrument.4.2 Sintered carbon-black doped PTFE samples are alsocommercially available7and are described in Table 2. Thesematerials provide
20、 close approximation to the optical propertiesof a perfect reflecting diffuser with spectrally neutral absor-bance features and may be used to transfer a scale of linearityin reflectance factor to another material or instrument.5. Significance and Use5.1 Most commercial reflectometers and spectropho
21、tom-eters with reflectance capability measure relative reflectance.The instrument reading is the ratio of the measured radiationreflected from the reference specimen to the measured radia-tion reflected by the test specimen. That ratio is dependent onspecific instrument parameters.5.2 National stand
22、ardizing laboratories and some researchlaboratories measure reflectance on instruments calibratedfrom basic principles, thereby establishing a scale of absolutereflectance as described in CIE Publication No. 44 (5). Thesemeasurements are sufficiently difficult and of prohibitive costthat they are us
23、ually left to laboratories that specialize in them.5.3 A standard that has been measured on an absolute scalecould be used to transfer that scale to a reflectometer. Whilesuch procedures exist, the constraints placed on the mechanicalproperties restrict the suitability of some of the optical prop-er
24、ties, especially those properties related to the geometricdistribution of reflected radiation. Thus, reflectance factorstandards that are sufficiently rugged or cleanable to use aspermanent transfer standards, with the exception of the sinteredPTFE standards, depart considerably from the perfect dif
25、fuserin the geometric distribution of reflected radiation.5.4 The geometric distribution of reflected radiance fromsuch standards is sufficiently diffuse that such a standard canprovide a dependable calibration of a directional-hemisphericalor certain directional-directional reflectometers. Although
26、pressed powder standards are subject to contamination and6Such material is available under the trade name Spectralon SRS-99 fromLabsphere, Inc., P.O. Box 70, North Sutton, NH 03260-0070.7Such material is available under the trade name Spectralon SRS-XX fromLabsphere, Inc., P.O. Box 70, North Sutton,
27、 NH 03260-0070.TABLE 1 6/Typical Diffuse Reflectance for Sintered (LabsphereSpectralonY SRS-99)AWavelength, nm Reflectance Factor250 0.940300 0.977400 0.991500 0.991600 0.991700 0.990800 0.991900 0.9911000 0.9901100 0.9901200 0.9891300 0.9881400 0.9861500 0.9881600 0.9871700 0.9841800 0.9841900 0.97
28、82000 0.9702100 0.9502200 0.9632300 0.9552400 0.9442500 0.940Density = 1500 kg/m3; thickness $ 7 mm.AAvailable from Labsphere, Inc., P.O. Box 70, North Sutton, NH 03260-0070;uncertainty of measurement 60.002.TABLE 2 6/Typical Diffuse Reflectance for Three SinteredCarbon-Black Doped PTFE (Labsphere S
29、pectralonY SRS-80,SRS-10, and SRS-02)AWavelength, nm SRS-80 SRS-10 SRS-02250 0.774 0.106 0.015300 0.793 0.099 0.016400 0.795 0.097 0.017500 0.796 0.099 0.017600 0.797 0.101 0.017700 0.799 0.103 0.017800 0.802 0.105 0.018900 0.803 0.105 0.0171000 0.805 0.106 0.0181100 0.806 0.108 0.0171200 0.807 0.10
30、9 0.0181300 0.808 0.111 0.0181400 0.808 0.112 0.0181500 0.810 0.113 0.0201600 0.811 0.114 0.0211700 0.812 0.115 0.0231800 0.813 0.116 0.0241900 0.811 0.118 0.0262000 0.814 0.117 0.0272100 0.809 0.114 0.0302200 0.812 0.110 0.0322300 0.813 0.110 0.0352400 0.809 0.103 0.0342500 0.809 0.101 0.038thickne
31、ss #7 mm thickness #5 mm thickness #3mmAAvailable from Labsphere, Inc., P.O. Box 70, North Sutton, NH 03260-0070.Materials are available in nominal reflectance factor values at 600 nm frombetween 0.02 and 0.99.E 17912breakage, the reflectance factor of pressed powder can besufficiently reproducible
32、from specimen to specimen from agiven lot of powder to allow the assignment of absolutereflectance factor values to all of the powder in a lot.5.5 Sintered PTFE materials exhibit sufficient reproducibil-ity from within the same specimen after resurfacing or cleaningthe specimen to allow the assignme
33、nt of absolute reflectancefactor values.5.6 Preparation of packed powder reflectance standards iscovered in Practice E 259. This practice describes the spectraland physical properties of these materials and of the sinteredPTFE materials.6. Apparatus6.1 The basic apparatus for preparing pressed powde
34、r stan-dards includes a powder press, powder containers, and ananalytical balance. Powder presses suitable for the productionof standards are commercially available.86.2 Sintered PTFE specimens, both white and for linearitytesting, are commercially available.6,77. Handling Procedures7.1 Pressed plaq
35、ues should be kept in a dessicator when notin use. Pressed powder samples of both barium sulfate andPTFE are prone to particulate contamination and electrostati-cally attract airborne particles. Packed PTFE powder is alsosusceptible to absorbing vapors from organic solvents. All suchcontaminants can
36、 make these materials slightly luminescentand reduce reflectance in the ultraviolet and NIR regions.Typical reflectance data for pressed barium sulfate and pressedPTFE powder are given in Table 3.7.2 Sintered PTFE plaques or standards should be kept in aclean, dust-free environment when not in use.
37、Higher reflec-tance specimens are prone to particulate contamination andelectrostatically attract airborne particles. Sintered PTFEsamples are also susceptible to absorbing vapors from organicsolvents. Such contaminants can make these materials slightlyluminescent and reduce reflectance in the ultra
38、violet and NIRregions. Typical reflectance data for sintered PTFE materialsare given in Table 1 and for a range of sintered carbon-blackdoped PTFE are given in Table 2.8. Precision and Bias8.1 The National Institute for Standards and Technology(NIST) and the Intersociety Color Council Project Commit
39、tee22, Materials for Instrument Calibration, have conductedcollaborative tests to determine the precision and bias of thepreparation of PTFE reflectance factor standards (6-8). Thestandard deviation of three determinations of the reflectancefactor of PTFE by NIST ranged from 0.0002 to 0.0008 over th
40、espectral range from 300 to 1000 nm. The measured reflectanceof PTFE from two manufacturers exhibited differences offrom 0.002 to +0.004 over the same range, with the largestdifferences near the ends of the range and a constant measure-ment uncertainty of 60.005.8.2 The CIE Publication Number 46 (1)
41、 cites literaturereferences on the reproducibility of barium sulfate pressingsthat range from 0.05 to 1.0 %, with the most common valuebeing 0.2 %. This puts the reproducibility of the plaquepreparation near the level of the reproducibility of the interna-tional standardizing laboratories ability to
42、 characterize theabsolute reflectance of the material.8.3 Collaborative studies have not been conducted on thesintered PTFE or carbon-black doped PTFE materials. How-ever, these materials are now being supplied as calibratedtransfer standards by both the National Physical Laboratory8Powder presses f
43、or making acceptable standards are available from Carl ZeissCanada, Ltd., 45 Valleybrook Drive, Don Mill, Ontario M3B 2S6, Canada, Part No.505866; Technidyne Corp., 100 Quality Avenue, New Albany, IN 47150-2272, PartNo. 176601; and Labsphere, Inc., P.O. Box 70, North Sutton, NH 03260-0070, PartNo. P
44、SH-020.TABLE 3 6/Diffuse Reflectance Factor of Eastman-Kodak WhiteReflectanceAWavelength, nm Reflectance FactorStandard Pressed Barium Sulfate PowderB,C300 0.968350 0.979400 0.987450 0.991500 0.991550 0.992600 0.992650 0.992700 0.992750 0.992800 0.992850 0.991900 0.990950 0.9881000 0.986Pressed PTFE
45、 PowderD,E300 0.984400 0.993500 0.994600 0.994700 0.994800 0.994900 0.9941000 0.9941100 0.9941200 0.9931300 0.9921400 0.9911500 0.9921600 0.9921700 0.9901800 0.9901900 0.9852000 0.9812100 0.9682200 0.9772300 0.9722400 0.9622500 0.960AReflectance data for packed PTFE over certain wavelengths in the N
46、IR havebeen called into question. The data presented are those currently certified andused by NIST.BDensity = 2000 kg/m3; thickness = 5 mm.CAvailable from Eastman-Kodak Corp. as Kodak White Reflectance Stan-dard 6091, Eastman-Kodak Laboratory and Research Products, Rochester, NY14650.DDensity = 1000
47、 kg/m3; thickness $ 7 mm.EThe following PTFE powders have been found acceptable: PTFE-M-12 fromDaikin Industries, Ltd., 1-1 Nishihitotsuya Yodogawa, Siesakusho, Setto-Shi,Osaka (Japan); Teflon 7-A from E. I. Dupont de Nemours and Ausimont Algoflon F-5 and F-6, available fromAusimont USA, Inc., CN-18
48、38-T, Morristown, NJ 07960.E 17913(United Kingdom) and the NIST, with the standard blanksprovided by Labsphere, Inc.6,79. Keywords9.1 hemispherical optical measurement system; integratingsphere; materials standards; reflectance and reflectivity; Spec-tralony; transfer standardsREFERENCES(1) Publicat
49、ion CIE No. 46A Review of Publications on Properties andReflection Values of Material Reflection Standards, USNC-CIE, Na-tional Institute for Standards and Technology, Room B306/220,Gaithersburg, MD 20899.(2) Grum, F., and Saltzman, M., “A New White Standard of Reflectance,”Proceedings of the 18th Session of CIE, London, 1975; PublicationCIE No. 36, Bureau Central de la CIE, Paris, 1976, pp. 9198.(3) Weidner, V. R., and Hsia, J. J., “Reflection Properties of PressedPolytetrafluoroethylene Powder,” Journal of the Optical Society ofAmerica, Vol 71, 1981, pp. 856861.(4) Weidne
