The TSI Radiometer Facility: absolute calibrations for total solar irradiance instruments
The total solar irradiance (TSI) climate data record includes overlapping measurements from 10 spaceborne radiometers.
The continuity of this climate data record is essential for detecting potential long-term solar fluctuations, as offsets
between different instruments generally exceed the stated instrument uncertainties. The risk of loss of continuity in this
nearly 30-year record drives the need for future instruments with <0.01% uncertainty on a absolute scale. No facility
currently exists to calibrate a TSI instrument end-to-end for irradiance at solar power levels to these needed accuracy
levels. The new TSI Radiometer Facility (TRF) is intended to provide such calibrations. Based on a cryogenic
radiometer with a uniform input light source of solar irradiance power levels, the TRF allows direct comparisons
between a TSI instrument and a reference cryogenic radiometer viewing the same light beam in a common vacuum
system. We describe here the details of this facility designed to achieve 0.01% absolute accuracy.
This paper was published in SPIE Proceedings Vol. 6677