ASTM_E_1791_-_96_2014.pdf

Designation:E179196(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 adoption 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 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 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(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(6-8)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 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 preparation 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 for 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 asstandard.No other units of measurement are included in thisstandard.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 limitations prior to use.2.Referenced Documents2.1 ASTM Standards:3E131 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 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 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 E13.03 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 E1791 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 information,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 States1 detector and some measurable quantity provided by the system.(E131)3.2.2 near-infrared,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 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 senseor as an abbreviation for reflectance