Assessment of Instrument Performance of the FY3E/JTSIM/DARA Radiometer Through the Analysis of TSI Observations

Since the late 1970s, satellite missions have monitored Total Solar Irradiance (TSI), providing a long-term record of solar variability. The Digital Absolute Radiometer (DARA), onboard the Chinese FY3E spacecraft since 4 July 2021, contributes to extending this record. In this study, we evaluate DARA observations in both the World Radiometric Reference (WRR) and International System of Units (SI) scales, and compare them with VIRGO/PMO6, TSIS-1/TIM, and the Solar Irradiance Absolute Radiometer (SIAR), which is co-located on the same platform (FY3E/JTSIM). We identify and correct an artifact in the thermal aperture model caused by annual satellite maneuvers. A statistical analysis of the measurements in the SI or WRR scale shows that the mean value of the DARA TSI observations is lower than the ones recorded by the VIRGO/PMO6 and TSIS-1/TIM but higher than the SIAR measurements. We estimate a relatively small degradation of ∼49 ppm over 46 months due to the exposure of the instrument to the UV/EUV radiations. Finally, the corrected DARA observations are incorporated into the long-term TSI composite time series. Comparison with the PMOD/WRC composite shows only marginal differences (less than 0.015 W m−2), confirming the consistency and reliability of including the new TSI product (JTSIM-DARAv1).