Cited by 1.5kOpen Access
The National Bureau of Standards^was established by an act
National Institute of Standards and Technology
Publishes on Calibration and Measurement Techniques, Scientific Measurement and Uncertainty Evaluation, Spectroscopy and Laser Applications. 53 papers and 2.2k citations.
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The National Bureau of Standards^was established by an act
The reflection properties of pressed polytetrafluoroethylene powder have been under investigation by the Radiometric Physics Division at the National Bureau of Standards for the past five years. This material has a great potential use, both as a standard of diffuse reflectance and as a coating for integrating spheres for applications in reflectance spectrophotometry and other signal-averaging devices. It possesses certain physical and optical properties that make it ideal for use in these applications. Techniques are given for preparing reflection standards and coating integrating spheres with the pressed powder. The effects of powder density and thickness on its reflectance are reported, and observations of possible problems with fluorescence that are due to the presence of contaminants in the powder are discussed. The absolute reflectance (6°/hemispherical reflectance factor relative to a perfect diffuser) is reported for the spectral range of 200–2500 nm. The directional/hemispherical reflectance factor relative to 6°/hemispherical reflectance is given for several wavelengths in the ultraviolet and visible spectrum and for angles of incidence between 5 and 75°. The bidirectional reflectance factor is reported for 300, 600, and 1500 nm at angles of incidence of −10, −30, −50, and −70° and at viewing angles at 10° intervals from −80 to +80°.
Report issued by the U.S. National Bureau of Standards discussing specifications of reflectance and proposed nomenclature. As stated in the introduction, "this monograph presents a unified approach to the specification of reflectance in relation to the beam geometry of both the incident and the reflected flux in any reflectometer or in any application of measured reflectance data" (p. 1). This report includes illustrations.
The object of this paper is to present results of several experiments relating to the preparation and use of pressed polytetrafluoroethylene (PTFE) powder as a diffuse reflectance standard for the 200–2500-nm spectral range. These experiments include two round-robin intercomparisons involving nine laboratories. These round-robin experiments provided data on the variability of the reflectance of pressed PTFE reflectance standards prepared in different laboratories. Results of these measurements provided insight into the problems associated with the PTFE standards and helped to establish what practices needed to be standardized to improve interlaboratory agreement for diffuse reflectance measurements.
A thorough study and error analysis was made of the Van den Akker or "auxiliary sphere" method of determining a scale of directional-hemispherical reflectance factor. The effects of a non-Lambertian distribution of the reflected radiation, including retroreflection, were included in this study. Three working standards were measured to an uncertainty in reflectance of less than ±0.0015 and these will be used as a basis for a new, more accurate NBS scale of 6°-hemispherical reflectance factor. The new scale and the NBS scale established in 1965 are in agreement to within the uncertainty of ±0.005 assigned to the 1965 scale.