Methods for Quantitative Infrared Directional-Hemispherical and Diffuse Reflectance Measurements Using a Fourier Transform Spectrometer and a Commercial Integrating Sphere

Published

January 20, 2018

Author(s)

Leonard M. Hanssen, Thomas A. Blake, TImothy J. Johnson, Russell G. Tonkyn, Brenda M. Forland, Tanya L. Myers, Carolyn S. Brauer, Yin-Fong Su, Bruce E. Bernacki

Abstract

Infrared integrating sphere measurements of solid samples are important in providing reference data for contact, standoff and remote sensing applications. At the Pacific Northwest National Laboratory (PNNL) we have developed protocols to measure both the directional-hemispherical ( and diffuse (d) reflectances of powders, liquids, and disks of powders and solid materials using a commercially available, matte gold-coated integrating sphere and Fourier transform infrared spectrometer. Detailed descriptions of the sphere alignment and its use for making these reflectance measurements are given. Diffuse reflectance values were found to be dependent on the bidirectional reflection distribution function (BRDF) of the sample and the solid angle intercepted by the sphere’s specular exclusion port. To determine how well the sphere and protocols produce quantitative reflectance data, measurements were made of three diffuse and two specular standards prepared by the National institute of Standards and Technology (NIST, USA), a LabSphere Spectralon visible standard, a LabSphere Infragold standard, hand-packed sulfur powder samples, and water. The five NIST standards behaved as expected: the three diffuse standards had a high degree of “diffuseness,” d/ = D > 0.9, whereas the two specular standards had D ≤ 0.03. The average absolute differences between the NIST and PNNL standards for both directional- hemispherical and diffuse reflectance measurements are on the order of 0.01 reflectance units. Other quantitative differences between the PNNL- measured and calibration (where available) or literature reflectance values for these standards and materials are given and the origins of discrepancies are discussed. Random uncertainties and estimates of systematic uncertainties are presented. Corrections necessary to provide better agreement between the PNNL reflectance values as measured for the NIST standards and the NIST reflectance values for these same standards are also discusse

Citation

Applied Optics

Volume

57

Issue

3

Pub Type

Journals

Download Paper

https://doi.org/10.1364/AO.57.000432

Keywords

infrared, reflectance, diffuse, methods, integrating sphere, measurements

Citation

Hanssen, L. , Blake, T. , Johnson, T. , Tonkyn, R. , Forland, B. , Myers, T. , Brauer, C. , Su, Y. and Bernacki, B. (2018), Methods for Quantitative Infrared Directional-Hemispherical and Diffuse Reflectance Measurements Using a Fourier Transform Spectrometer and a Commercial Integrating Sphere, Applied Optics, [online], https://doi.org/10.1364/AO.57.000432 (Accessed December 22, 2024)