Exploring New Instrument deGradation Models and Algorithms (ENIGMA) for the SORCE–Solar Irradiance Monitor

Abstract

The Spectral Irradiance Monitor (SIM), on board the Solar Radiation and Climate Experiment (SORCE) test satellite operated for 17 years: from February 2003 to February 2020, measuring the Solar Spectral Irradiance from 200 to 2,400 nm. The unavoidable instrument degradation was tracked and corrected based on a measurement equation derived from accessible telemetry, the known instrument refraction geometry, inter-detector comparisons, and inter-spectrometer comparisons. While the previous degradation model captures much of the long-term trending, some of the parameters were adjusted without well-defined physical justifications. The development of enhanced SORCE/SIM measurement equations allowed the evaluation and inclusion of degradation mechanisms not captured in the original model. We present the multiple approaches tested to better understand the degradation mechanisms and the final model that was adopted with the underlying physical implications. An updated SORCE/SIM data product, L3 Enigma Version 1 (L3E V1), covering the lifetime of the mission, starting at 210.0 nm instead of 240.0 nm, and adjusted to the TSIS/SIM absolute irradiances, has been generated and made available to the community.