Total Solar Irradiance Instrument Validations Improve TSI Record
Greg Kopp [Greg.Kopp@lasp.colorado.edu], David Harber, and Karl Heuerman,
Laboratory for Atmospheric and Space Physics (LASP), University of Colorado, Boulder
The total solar irradiance (TSI) data record includes measurements from 10 spaceborne
instruments over the past 31 years. Overlap of on-orbit measurements allows adjustments for
instrument offsets to create a TSI composite needed for estimating solar influences on Earth
climate both via direct measurements over 11-year solar cycles and via solar proxies to
estimate historical forcings. The offsets between different TSI instruments are due to
calibration errors, as none of the current on-orbit instruments (as of the meeting’s abstract
submission deadline! ;-) have been calibrated end-to-end to the needed accuracy levels.
The new TSI Radiometer Facility (TRF) built for NASA’s Glory mission provides these
new calibration capabilities. Via direct optical power comparisons to a NIST-calibrated
cryogenic radiometer, this facility can provide calibrations of a TSI instrument much as the
instrument is operated in space: under vacuum, at full solar irradiance power levels, and with
uniform incoming light for irradiance measurements. Both the upcoming Glory Total
Irradiance Monitor and the PICARD/PREMOS instruments have been tested in this new
facility, helping improve the absolute accuracy of the TSI data record and diagnose the
causes of existing instrument offsets.