1、Designation: E 1791 96 (Reapproved 2008)e1Standard 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 oforigina
2、l 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.e1NOTETrademark names removed editorially in April 2008.INTRODUCTIONThe inter
3、nationally accepted standard of reflectance is the perfect 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
4、.Optical properties of standards prepared from pressed plaques 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 (
5、CIE) Publication No. 46 (5) . Additional transfer standards are 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-
6、8) fulfill this requirement. The principle uses of a reflectance 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
7、principles, should be quite easy. In practice, values are likely 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 prep
8、aration anduse of acceptable transfer standards for NIR spectrophotom-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 fo
9、r such calibra-tions because they have very stable reflectance 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 as thestandard. The values given in paren
10、theses are for informationonly.1.3 This standard does not purport 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 limitatio
11、ns prior to use.2. Referenced Documents2.1 ASTM Standards:3E 131 Terminology Relating to Molecular SpectroscopyE 259 Practice for Preparation of Pressed Powder WhiteReflectance Factor Transfer Standards for Hemisphericaland Bi-Directional GeometriesE 284 Terminology of Appearance3. Terminology3.1 De
12、finitionsTerms 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 radi
13、ant power incident on its1This practice is under the jurisdiction of ASTM Committee E13 on MolecularSpectroscopy and Separation Science and is the direct responsibility of Subcom-mittee E13.11 on Multivariate Analysis.Current edition approved March 15, 2008. Published April 2008. Originallyapproved
14、in 1996. Last previous edition approved in 2000 as E 1791 96 (2000).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 Boo
15、k of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.detector and some measurable quantity provided by the system.(E 131)3.2.2 near-inf
16、rared, adjthe region of the electromagneticspectrum 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 sa
17、me 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 senseor as an abbreviation for refle
18、ctance 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 spectralconditions of measurement (2)
19、.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.Reflectance data for this material are given in Table 1. Thesematerials provide close approximation to the opti
20、cal 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 available and are described in Table 2. Thesematerials provide close approximation to the opti
21、cal 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 spectrophotom-eters with reflectance capab
22、ility 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 standardizing laboratories and some r
23、esearchlaboratories 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 usually left to laboratories that
24、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-erties, especially those propertie
25、s 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 diffuserin the geometric distributi
26、on 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. Althoughpressed powder standards are sub
27、ject to contamination andbreakage, the reflectance factor of pressed powder can besufficiently reproducible 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.TABLE 1 6/Typical Diffuse Reflectance for Sintere
28、d PTFEWavelength, nm Reflectance Factor250 0.940300 0.977400 0.991500 0.991600 0.991700 0.990800 0.991900 0.9911000 0.9901100 0.9901200 0.9891300 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; thickne
29、ss $7mmTABLE 2 6/Typical Diffuse Reflectance for Three SinteredCarbon-Black Doped PTFEWavelength, nm 80 % Standard 10 % Standard 2 % Standard250 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.
30、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 0.0201600 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
31、0.813 0.110 0.0352400 0.809 0.103 0.0342500 0.809 0.101 0.038thickness #7 mm thickness #5 mm thickness #3mmE 1791 96 (2008)e125.5 Sintered PTFE materials exhibit sufficient reproducibil-ity from within the same specimen after resurfacing or cleaningthe specimen to allow the assignment of absolute re
32、flectancefactor 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 powder stan-dards incl
33、udes a powder press, powder containers, 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
34、 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 make these materials
35、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. Higher reflec-tance sp
36、ecimens 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 ultraviolet and NIRregions.
37、 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 Committee22, Materials for I
38、nstrument 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 thespectral range from 3
39、00 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) cites literaturerefer
40、ences 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 characterize theabsol
41、ute 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 Laboratory(United Kingdom) and the NIST, with the
42、 standard blanksprovided by Labsphere, 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 Re
43、flectance FactorStandard Pressed Barium 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 0.9
44、941100 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 presented are those currently certified andused by NIST.BDensity = 2000 kg/m3; thickness = 5 mm.CDensity = 1000 kg
45、/m3; thickness $7 mm.DThe 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, available from Ausimont USA,Inc., CN-1838-T, Morris
46、town, NJ 07960.E 1791 96 (2008)e13REFERENCES(1) Publication 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
47、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,
48、 Vol 71, 1981, pp. 856861.(4) Weidner, V. R., 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 Reflection Measure-ments, USNC-CIE,
49、National Institute for Standards and Technology,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.
