Abstract
Current uncertainty requirements for the measurement of global variables relevant to climate change modeling in the reflected solar range are 0.5 % to 1 % for solar and lunar spectral irradiance and 0.5 % to 2 % for Earth reflected radiance. Future uncertainty requirements, as defined by CLARREO mission requirements, include laboratory calibration uncertainties are 0.2 % over the 500 nm to 900 nm spectral range and 1 % or less over the rest of the spectral region from 320 nm to 2300 nm. The uncertainties in lamp-illuminated integrating spheres, a principal calibration artifact, ranging from 2% to 3 % in the visible to near-infrared and 3 % to 5 % in the short-wave infrared, do not meet either current or future uncertainty requirements.
NIST uncertainties in broad-band lamp-based calibration artifacts are traceable to primary standard blackbodies. The irradiance and radiance responsivity scales disseminated by the NIST laser-based SIRCUS calibration facility are held by primary standard irradiance meters traceable to the Primary Optical Watt Radiometer and dimensional metrology from the NIST Aperture Area Facility. The SIRCUS facility has demonstrated that moving from source-based scales traceable to primary standard blackbodies to detector-based scales offer opportunities to reduce the uncertainties in disseminated standards.
This presentation discusses existing primary radiometric standards and the uncertainties in detector-based radiance and irradiance scales, validation of their uncertainty budgets through measurements of primary standard metal melting point blackbodies, development of low temperature active cavity radiometers operating in irradiance mode, and the development of transfer standard spectrographs. Finally, this paper discusses possible further developments at NIST aimed at supporting future climate benchmark instrument uncertainty requirements.
Advances in SI-traceable Detector Standards for the Reflected Solar Region
Current uncertainty requirements for the measurement of global variables relevant to climate change modeling in the reflected solar range are 0.5 % to 1 % for solar and lunar spectral irradiance and 0.5 % to 2 % for Earth reflected radiance. Future uncertainty requirements, as defined by CLARREO mission requirements, include laboratory calibration uncertainties are 0.2 % over the 500 nm to 900 nm spectral range and 1 % or less over the rest of the spectral region from 320 nm to 2300 nm. The uncertainties in lamp-illuminated integrating spheres, a principal calibration artifact, ranging from 2% to 3 % in the visible to near-infrared and 3 % to 5 % in the short-wave infrared, do not meet either current or future uncertainty requirements.
NIST uncertainties in broad-band lamp-based calibration artifacts are traceable to primary standard blackbodies. The irradiance and radiance responsivity scales disseminated by the NIST laser-based SIRCUS calibration facility are held by primary standard irradiance meters traceable to the Primary Optical Watt Radiometer and dimensional metrology from the NIST Aperture Area Facility. The SIRCUS facility has demonstrated that moving from source-based scales traceable to primary standard blackbodies to detector-based scales offer opportunities to reduce the uncertainties in disseminated standards.
This presentation discusses existing primary radiometric standards and the uncertainties in detector-based radiance and irradiance scales, validation of their uncertainty budgets through measurements of primary standard metal melting point blackbodies, development of low temperature active cavity radiometers operating in irradiance mode, and the development of transfer standard spectrographs. Finally, this paper discusses possible further developments at NIST aimed at supporting future climate benchmark instrument uncertainty requirements.