Accurate, long-term solar spectral irradiance (SSI) measurements are vital for interpreting how solar variability affects the balance of the Earth’s total energy budget and for validating climate model sensitivities to spectrally varying solar forcing. Ultimately, understanding these effects requires continuous measurements of SSI that meet the stringent requirements of climate-quality accuracy and stability over time.
Long-term, continuous measurements of nearly full spectrum SSI began with the SORCE mission (in operation since 2003). The SORCE SSI dataset has provided valuable information in improving solar spectral models, particularly on short time scales. However, there is presently much debate about the long-term SSI variability record to definitively establish the long-term (decadal) solar impact on wavelength-dependent climate processes. Major instrument and measurement challenges in quantifying the influence of SSI variability on climate are achieving high radiometric absolute accuracy and then maintaining (on-orbit) the long-term stability of the measurement record.
Recent LASP advancements in calibration facilities and techniques make it now possible to improve significantly the accuracy and traceability of future SSI observations and assure quantification of uncertainties as input to increasingly more sophisticated climate models. The Total and Spectral Solar Irradiance Sensor (TSIS) Spectral Irradiance Monitor (SIM) is the next generation, space-borne SSI radiometer that is scheduled to be operational on the International Space Station (ISS) in late 2017. The instrument has been unit-level calibrated and end-to-end validated to achieve unprecedented levels of absolute accuracy and high spectral stability.
Going forward, we are leading an instrument development that will couple with advances in small satellite technology to potentially mitigate future SSI data continuity risks. This compact SSI instrument (utilizing new manufacturing and material advances) will offer significant implementation flexibility for future alternative flight opportunities, including CubeSat missions. It represents a cost-effective alternative to maintain high priority SSI measurements and will provide an SI-traceable tie to existing and future satellite records.