Skip to main content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Optical reflectance of pyrheliometer absorption cavities: progress towards SI-traceable measurements of solar irradiance

Published

Author(s)

Heather J. Patrick, Thomas A. Germer, Clarence J. Zarobila, Catherine C. Cooksey, Howard W. Yoon

Abstract

We have accurately determined the absorptance of three pyrheliometer cavities at 532 nm by measuring the residual reflectance using an angle-resolved bidirectional reflectometer. Measurements were performed at normal incidence as a function of viewing angle and position on the cavity cone. By numerically integrating the measured angle resolved scatter (ARS) over both direction and position and accounting for an obstructed view of the cavity, we determined that the effective cavity reflectance was between 0.08 % and 0.09 %. Thus, the absorbtance of the three cavities ranged from 99.909 (0.014) % to 99.922 (0.012) % where the value in parentheses indicates the k=2 expanded uncertainty. These measurements, when extended over the spectral range of operation of the pyrheliometer, are required to establish traceability for absolute solar irradiance measurements.
Citation
Applied Optics
Volume
55
Issue
23

Keywords

reflectance, scattering, solar, irradiance, BRDF, goniometer, directional-hemispherical reflectance, diffuse reflectance
Created August 8, 2016, Updated November 10, 2018