Exploring New Instrument deGradation Models and Algorithms (ENIGMA)

The Solar Radiation and Climate Experiment measured Total Solar Irradiance (TSI) and Solar Spectral Irradiance (SSI) from 2003 to 2020. The Solar Irradiance Monitor (SIM) instrument measured SSI from 200nm to 2400 nm on a daily basis. The current SORCE-SIMinstrument degradation correction uses a measurement equation derived fromaccessible telemetry, the known instrument refraction geometry, inter-detector comparisons,and inter-spectrometer comparisons. While the current degradation model captures much of thelong-term trending, some of the parameters were adjusted without well-defined physicalinterpretations.The degradation model used for SORCE-SIM is not unique. We're reporting on work to Explore NewInstrument degradation Models and Algorithms (ENIGMA) to address issues with the currentmodel and with the derived corrected irradiances. The development of enhanced SORCE-SIMmeasurement equations permits the evaluation, and potential inclusion, of degradationmechanisms not captured in the present model.We present an initial updated degradation model which improves our ability to construct a composite irradiance time series in combination with TSIS-SIM, whose measurements overlap with SORCE for 2 years and has well-defined uncertainties. Combining the two datasets, allowedthe construction of a consistent composite irradiance time series from 2003-2023.