Singular Spectrum Analysis to Correct the Seasonal Variation in the FCDR of FY-3A/B/C VIRR Reflective Solar Bands

The Visible and Infrared Radiometer (VIRR) onboard China’s Fengyun-3A/B/C (FY-3A/B/C) satellites has delivered essential global Earth observations for over 15 years, enabling critical applications in cloud dynamics research, vegetation assessment, and environmental monitoring. However, VIRR lacks onboard calibration systems for its visible/near-infrared channels, which results in progressive radiometric degradation due to cumulative space radiation and detector aging, challenging the generation of stable long-term climate datasets [e.g., the fundamental climate data record (FCDR)]. By integrating simultaneous nadir overpass (SNO) cross-calibration technique with references from Aqua’s Moderate Resolution Imaging Spectroradiometer (MODIS), we identified pronounced seasonal fluctuations in long-term recalibration coefficients, particularly for the 0.86 μm. To isolate these effects, singular spectrum analysis (SSA) was used to decompose the coefficient series into three components: trend, seasonal fluctuations, and residuals. A hybrid calibration model was then formulated by integrating the isolated trend and seasonal features. Validation across globally distributed pseudo-invariant sites confirmed enhanced radiometric stability. The work highlights the necessity of accounting for seasonally modulated calibration artifacts, which were previously unaddressed in operational protocols, to ensure the stability and accuracy of climate data records (CDRs).