1、Designation: E1791 96 (Reapproved 2014)Standard Practice forTransfer Standards for Reflectance Factor for Near-InfraredInstruments Using Hemispherical Geometry1This standard is issued under the fixed designation E1791; the number immediately following the designation indicates the year oforiginal ad
2、option or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONThe internationally accepted standard of reflectance is the perfect re
3、flecting 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 plaque
4、s 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 Commission Internationale deLEclairage (CIE) Publication No. 46 (5). Additional transfer standards ar
5、e required that have a verystable reflectance factor that is constant with wavelength and that have a range of values from nearzero to close to that of the perfect reflecting diffuser. Such materials as carbon-black doped sinteredPTFE (6-8) fulfill this requirement. The principle uses of a reflectan
6、ce factor standard are fortransferring 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 fromfirst principles, should be quite easy. In practice, values are like
7、ly to be required for parameters thatare unknown, proprietary, or require a highly sophisticated level of skill. Some, but not all, of theseparameters are discussed in this practice.1. Scope1.1 This practice covers procedures for the preparation anduse of acceptable transfer standards for NIR spectr
8、ophotom-eters. 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
9、 factors that arenearly 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 asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purpo
10、rt to address 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:3E131
11、 Terminology Relating to Molecular SpectroscopyE259 Practice for Preparation of Pressed Powder WhiteReflectance Factor Transfer Standards for Hemisphericaland Bi-Directional GeometriesE284 Terminology of Appearance3. Terminology3.1 DefinitionsTerms and definitions in TerminologyE284 are applicable t
12、o 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 incident on its1This practice is under the jurisdiction o
13、f ASTM Committee E13 on MolecularSpectroscopy 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. Originallyapproved in 1996. Last previous edition approved in 2008 as E1
14、791 96 (2008)1.DOI: 10.1520/E1791-96R14.2The boldface numbers in parentheses refer to the list of references at the end ofthis practice.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume in
15、formation, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1detector and some measurable quantity provided by the system.(E131)3.2.2 near-infrared, adjthe region of the el
16、ectromagneticspectrum for radiation of wavelengths between 780 and 2500nm (0.78 and 2.50 m).3.2.3 perfect reflecting diffuserideal reflecting surface thatneither absorbs nor transmits light, but reflects diffusely, withthe radiance of the reflecting surface being the same for allreflecting angles, r
17、egardless 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 senseor as an abbreviation for reflectance factor. Such usage may
18、beassumed unless the definition is specifically required by thecontext.3.2.5 reflectance factor, R, nratio of the flux reflected fromthe specimen to the flux reflected from the perfect reflectingdiffuser under the same geometric and spectral conditions ofmeasurement (2).4. Summary of Practice4.1 Pro
19、cedures for the preparation of packed powdersamples of barium sulfate and PTFE can be found in PracticeE259. Sintered PTFE samples are commercially available.Reflectance data for this material are given in Table 1. Thesematerials provide close approximation to the optical propertiesof the perfect re
20、flecting 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 available and are described in Table 2. Thesematerials provide close approximation to the optical propertiesof a perfect refl
21、ecting 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 spectrophotom-eters with reflectance capability measure relative reflecta
22、nce.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 standardizing laboratories and some researchlaboratories measure ref
23、lectance 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 usually left to laboratories that specialize in them.5.3 A standa
24、rd 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 opticalproperties, especially those properties related to the geometricdistrib
25、ution 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 diffuserin the geometric distribution of reflected radiation.5.4 The
26、 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. Althoughpressed powder standards are subject to contamination andbreakage
27、, the reflectance factor of pressed powder can besufficiently reproducible from specimen to specimen from aTABLE 1 6/Typical Diffuse Reflectance for Sintered PTFEWavelength, nm Reflectance Factor250 0.940300 0.977400 0.991500 0.991600 0.991700 0.990800 0.991900 0.9911000 0.9901100 0.9901200 0.989130
28、0 0.9881400 0.9861500 0.9881600 0.9871700 0.9841800 0.9841900 0.9782000 0.9702100 0.9502200 0.9632300 0.9552400 0.9442500 0.940Density = 1500 kg/m3; thickness $7mmTABLE 2 6/Typical Diffuse Reflectance for Three SinteredCarbon-Black Doped PTFEWavelength, nm 80 % Standard 10 % Standard 2 % Standard250
29、 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 0.109 0.0181300 0.808 0.111 0.0181400 0.808 0.112 0.0181500 0.810 0.113 0.020160
30、0 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 0.038thickness #7 mm thickness #5 mm thickness #3mmE1791 96 (2014)2given lot of powder t
31、o 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 assignment of absolute reflectancefactor values.5.6 Preparati
32、on of packed powder reflectance standards iscovered in Practice E259. This practice describes the spectraland physical properties of these materials and of the sinteredPTFE materials.6. Apparatus6.1 The basic apparatus for preparing pressed powder stan-dards includes a powder press, powder container
33、s, and ananalytical balance. Powder presses suitable for the productionof standards are commercially available.6.2 Sintered PTFE specimens, both white and for linearitytesting, are commercially available.7. Handling Procedures7.1 Pressed plaques should be kept in a dessicator when notin use. Pressed
34、 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 make these materials slightly luminescentand reduce reflec
35、tance 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. Higher reflec-tance specimens are prone to particulate cont
36、amination 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 ultraviolet and NIRregions. Typical reflectance data for sintere
37、d 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 Committee22, Materials for Instrument Calibration, have conducted
38、collaborative 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 thespectral range from 300 to 1000 nm. The measured reflectan
39、ceof 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) cites literaturereferences on the reproducibility of bariu
40、m 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 characterize theabsolute reflectance of the material.8.3 C
41、ollaborative studies have not been conducted on thesintered PTFE or carbon-black doped PTFE materials.However, these materials are now being supplied as calibratedtransfer standards by both the National Physical Laboratory(United Kingdom) and the NIST, with the standard blanksprovided by Labsphere,
42、Inc.9. Keywords9.1 hemispherical optical measurement system; integratingsphere; materials standards; reflectance and reflectivity; trans-fer standardsTABLE 3 6/Diffuse Reflectance Factor of Eastman-Kodak WhiteReflectance Poder (Barium Sulfate)AWavelength, nm Reflectance FactorStandard Pressed Barium
43、 Sulfate PowderB,300 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 0.986Reflectance of Pressed PTFE PowderC,D300 0.984400 0.993500 0.994600 0.994700 0.994800 0.994900 0.9941000 0.9941100 0.9941200 0.9931300 0.9921400 0.
44、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 presented are those currently certified andused by NIST.BDensity = 2000 kg/m3; thickness = 5 mm.CDensity = 1000 kg/m3; thickness $7 mm.DThe following PTF
45、E 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, available from Ausimont USA,Inc., CN-1838-T, Morristown, NJ 07960.E1791 96 (2014)3REFERENC
46、ES(1) Publication CIE No. 46A Review of Publications on Properties andReflection Values of Material Reflection Standards, USNC-CIE,National Institute for Standards and Technology, Room B306/220,Gaithersburg, MD 20899.(2) Grum, F., and Saltzman, M., “ANew White Standard of Reflectance,”Proceedings of
47、 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) Weidner, V. R.,
48、 Hsia, J. J., and Adams, B., “Laboratory Intercompari-son Study of Pressed Polytetrafluoroethylene Powder ReflectanceStandards,” Applied Optics, Vol 24, 1985, pp. 22252230.(5) Publication CIE No. 44Absolute Methods for ReflectionMeasurements, USNC-CIE, National Institute for Standards andTechnology,
49、 Room B306/220, Gaithersburg, MD 20899.(6) Springsteen, A. W., Ricker, T. M., and Leland, J. E., Guide toReflectance Materials and Coatings, Labsphere Technical Guide,North Sutton, NH, 1993.(7) Weidner, V. R., Hsia, J. J., and Eckerle, K. L., “Exploratory Researchin Reflectance and Fluorescence Standards at the National Bureau ofStandards,” Optics News, November 1986, p. 18.(8) V. R., Weidner, “Gray Scale of Diffuse Reflectance for the 2502500nm. Wavelength Range,” Applied Optics, Vol 25, No. 8, 1986, pp.12651266.(9) Publication CIE No. 44Radiometric and Pho
