An integrating-sphere reflectometer for the determination of absolute hemispherical spectral reflectance

Gene A. Zerlaut, A. C. Krupnick

An instrument for measuring the absolute hemispherical spectral reflectance of surfaces was designed. It possesses the ability to measure and monitor the absolute reflectance of a magnesium oxide or other standard and to compare this reflectance with that of any other surface. The theory is a modification of the analyses of Preston^{4} and of Middleton and Sanders.^{5} The error in their absolute methods - the inability to insure the surface of the magnesium oxide standard and the surface of the magnesium oxide-smoked sphere possess exactly the same reflectance - essentially has been eliminated by designing the integrating sphere such that its reflectance and that of the sample each can be measured in terms of other. The absolute reflectance of the standard can then be determined by one of two methods: 1) smoking either/or both the standard and the sphere until their reflectances are exactly equal or 2) substituting the ratio of their reflectances into an algebraic expression. © 1966 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

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Materials
Curve 1
Temperature K: ~298 Wavelength Range, µm: 0.259-2.20 Geometry θ': ~7° 2π Composition (weight percent), Specifications, and Remarks: Freshly shaved block; data extracted from smooth curve; data measured for both R(~7°, 2π) and R(2π, ~7°).
Curve 1
Temperature, K: ~298 Wavelength Range, µm: 0.256-2.36 Geometry θ θ' ω': ~7° 2π Composition (weight percent), Specifications, and Remarks: MgO (2 mm thick) on aluminum substrate; freshly smoked; data extracted from smooth curve; measured relative to MgO.