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 nearambient thermal emission sources, providing traceability in spatially and spectrally resolved radiance temperature, spectral radiance, and background-corrected effective emissivity. S. N. Mekhontsev (B) · L. M. Hanssen Optical Technology Division (844), National

Evaluation of Blackbody Cavity Emissivity in the Infrared Using Total Integrated Scatter Measurements

“…The results obtained are complementary to those from other tools available, including Monte Carlo ray-trace modeling, finite-element thermal modeling analysis, and direct spectral radiance measurement comparisons with other well-characterized blackbodies [17,1]. Experimentally determined values for emissivity, using both direct and indirect methods, enable us to avoid the use of incorrect emissivity values, resulting from approximations and perhaps incorrect assumptions about the cavity coating properties and exact cavity geometry.…”

“…These are: (1) the Advanced Infrared Radiometry and Imaging (AIRI) facility for spectral radiance, radiance temperature, and radiance temperature responsivity [1,2]; and (2) the Fourier Transform Infrared Spectrophotometry (FTIS) facility for optical properties of materials including, specifically, spectral emissivity [3]. Both systems rely on blackbody sources as references of spectral radiance.…”

Measurements of infrared spectral directional emittance at NIST - A status update

“…[6] However, later the fixed-point sources were transferred to the new NIST Advanced Infrared Radiometry and Imaging (AIRI) facility. [7] Since that time, the temperature scale is derived from the AIRI transfer standard radiation thermometers RT900 and RT1550 operating at 900 nm and 1550 nm, respectively. [8] These thermometers are used to calibrate a set of variable temperature blackbody reference sources, which are temperature-stabilized and -monitored by pairs of reference Platinum thermometers imbedded in the thermowells of each BB's heat pipe (HP).…”

Radiometic Comparison Between a National Laboratory and an Industrial Laboratory

“…The NIST TRT calibration was performed using variable temperature blackbodies as the transfer standard [7][8][9][10][11][12]. The following section discusses the results of this calibration.…”