NIST Radiance Temperature and Infrared Spectral Radiance Scales at Near-Ambient Temperatures

Abstract

The realization and the dissemination of spectral radiance and radiance temperature scales in the temperature range of −50 to 250°C and spectral range of 3–13 μm at the National Institute of Standards and Technology are described. The scale is source-based and is established using a suite of blackbody radiation sources, the emissivity and temperature of which have been thoroughly investigated. The blackbody emissivity was measured using the complementary approaches of modeling, reflectometry, and the intercomparison of the spectral radiance of sources with different cavity geometries and coatings. Temperature measurements are based on platinum resistance thermometers and on the direct use of the phase transitions of pure metals. Secondary sources are calibrated using reference blackbody sources, a spectral comparator, a controlled-background plate, and a motion control system. Included experimental data on the performance of transfer standard blackbodies indicate the need for development of a recommended practice for their specification and evaluation. Introduced services help to establish a nationwide uniformity in metrology of near-ambient thermal emission sources, providing traceability in spatially and spectrally resolved radiance temperature, spectral radiance, and background-corrected effective emissivity.