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-SIM
instrument degradation correction uses a measurement equation derived from
accessible telemetry, the known instrument refraction geometry, inter-detector comparisons,
and inter-spectrometer comparisons. While the current degradation model captures much of the
long-term trending, some of the parameters were adjusted without well-defined physical
interpretations.

The degradation model used for SORCE-SIM is not unique. We're reporting on work to Explore New
Instrument degradation Models and Algorithms (ENIGMA) to address issues with the current
model and with the derived corrected irradiances. The development of enhanced SORCE-SIM
measurement equations permits the evaluation, and potential inclusion, of degradation
mechanisms 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, allowed
the construction of a consistent composite irradiance time series from 2003-2023.