TSIS on the International Space Station: Continuity of the Solar Irradiance Data Record

The Total and Spectral Solar Irradiance Sensor (TSIS), first selected in 1998 for the National Polar-orbiting Operational Environmental Satellite System (NPOESS), re-manifested in 2010 on the NOAA-NASA Joint Polar Satellite System (JPSS), then the NOAA Polar Free Flyer, is now scheduled to be implemented as part of the newly established Solar Irradiance, Data and Rescue (SIDAR) program with a launch in 2017 to the International Space Station. The TSIS will acquire measurements of total and spectral solar irradiance (TSI and SSI, respectively). TSI is required for establishing Earth's total energy input while SSI is needed to understand how the atmosphere responds to changes in the Sun's output. Solar irradiance is one of the longest and most fundamental of all climate data records derived from space-based observations.

TSIS provides continuation of the Total Irradiance Monitor (TIM) and the Spectral Irradiance Monitor (SIM), currently flying on the NASA Solar Radiation and Climate Experiment (SORCE). Launched in 2003, SORCE is now more than six years beyond its prime-mission lifetime. The launch failure of the NASA Glory mission in 2011 coupled with diminished battery capacity on SORCE and delays in the launch of TSIS have put the continuous 36-year TSI record at risk. In 2012, a plan to maintain continuity of the TSI calibration scale between SORCE and TSIS was rapidly implemented through the USAF Space Test Program STPSat-3 that launched in late 2013. The shorter SSI record faces a likely gap between SORCE and TSIS.

This paper summarizes the importance of highly accurate and stable observations of solar irradiance in understanding the present climate epoch and for predicting future climate; why continuity in the solar irradiance data record is required; improvements in the TSIS TIM and SIM, including their traceability to ground-based cryogenic standards; and the maturity and implications of transitioning solar irradiance data records from research-to-operations.