TSIS-1 SIM L3 V13 Solar Spectral Irradiance

NASA’s Total and Spectral Solar Irradiance Sensor-1 (TSIS-1) operates on the International Space Station. TSIS-1 provides absolute measurements of the total solar irradiance (TSI) and spectral solar irradiance (SSI), important for accurate scientific models of climate change and solar variability. TSIS-1 is comprised of two instruments, the Total Irradiance Monitor (TIM), and the Spectral Irradiance Monitor (SIM).

This repository archives Version 13 (V13) of the TSIS-1 SIM Level 3 (L3) data release, and contains SSI in two cadences, 12-hour, and 24-hour. The TSIS-1 SIM L3 V13 data release contains data from 2018-03-14 to 2025-09-16.

Version 13 (V13) addresses data issues resulting from anomalies in the TSIS-1 SIM Digital Signal Processor (DSP) and the Electrical Substitution Radiometers (ESRs) that occurred in September and October 2024. The SIM DSP stopped responding to ground commands on September 4, 2023, and command and control were restored on October 21, 2023. Post-anomaly checkout revealed changes in ESR responsivity for certain configurations and wavelength ranges. Data affected in these ESR wavelength regions are corrected and first published in V13.

The TSIS-1 SIM ESRs are used directly for all reported solar spectral irradiances (SSIs) at wavelengths longer than 1620 nm. Prior to V13, ESR data were also used as the irradiance reference for diode measurements between 408 and 1620 nm. V13 addresses the ESR anomaly in two key ways: (1) ESR data collected after the anomaly are no longer used to correct diode degradation in the 408–1620 nm range, and a diode degradation model is used instead; and (2) for all SSIs longer than 1620 nm after September 4, 2023, a wavelength-dependent spectral correction is applied to the measured ESR irradiances.

As a consequence of the DSP anomaly, the Channel-C scans scheduled for October 2023 were not performed. However, Channel-C scans were successfully completed in April 2024 and October 2024. Degradation correction updates in V13 incorporate updated Channel-C diode data from the April 2023, April 2024, and October 2024 calibration campaigns, which were not included in V12.

The exact relationship between the DSP and ESR anomalies remains unclear, as ESR telemetry did not exhibit anomalous behavior until after SIM was power cycled on October 21, 2023. Following the ESR anomaly, the SIM ESRs exhibited wavelength- and channel-pairing-dependent changes. For the A_B and B_A channel pairings, these manifest as static offset changes, while the Channel-C ESR exhibits a time-dependent behavior.

A minor re-release of V13 was issued on September 3, 2025, to improve wavelength alignment in SIM V13 data products. Following the initial V13 release in January 2025, the thermal pointing system began exhibiting more frequent pointing excursions near zero crossings. These excursions reduced the algorithm’s ability to accurately determine spectral wavelength alignment, with the most pronounced effects observed in the 800–950 nm range and near 400 nm. As a result, data collected after the ESR anomaly were reprocessed to improve wavelength alignment in the final V13 data products.

See the release notes TSIS_SIM_V13_Release_Notes_V2.pdf or the TSIS SIM Data Products Release Notes page (https://lasp.colorado.edu/tsis/data/ssi-data/sim-ssi-release-notes/) for further details, and instructions for obtaining the latest TSIS-1 SIM L3 data release.

Data is archived in ASCII, netCDF, and IDL SAVfile format.