Ensuring continuous high-precision Earth Radiation Budget Records: a scene-dependent spectral fusion unfiltering framework for FY-3F ERM-II

Broadband radiance unfiltering, the spectral restoration of filtered sensor observations, is a fundamental prerequisite for accurate Earth Radiation Budget (ERB) quantification. The newly launched FY-3F Earth Radiation Measurement-II (ERM-II) instrument introduces a dedicated longwave channel, expanding spectral dimensionality beyond its predecessors and necessitating a specialized retrieval framework. This study establishes an operational, scene-dependent unfiltering model for ERM-II that explicitly addresses sensor-specific optical characteristics. A comprehensive spectral library was generated using radiative transfer simulations driven by high-precision global priors. Crucially, to mitigate radiometric distortion caused by sub-pixel scene heterogeneity, we implemented a Point Spread Function (PSF)-weighted convolution scheme. This method integrates collocated high-resolution MERSI-III cloud masks to accurately characterize the effective scene radiance perceived by the ERM-II detector. Based on this framework, optimal unfiltering architectures were determined: a linear fusion of shortwave and total channels for shortwave unfiltering, and distinct single-channel strategies for daytime (linear) and nighttime (nonlinear) longwave retrieval. Validation against Clouds and Earth’s Radiant Energy System (CERES) products demonstrates that the proposed multi-channel fusion effectively compensates for spectral response mismatches. The model achieves a coefficient of determination (R2) exceeding 0.96, with RMSEs constrained below 2.1 W⋅m−2⋅sr−1 and absolute biases within 0.21–1.59 W⋅m−2⋅sr−1. These results represent a substantial quantitative improvement over legacy FY-3C algorithms, reducing systematic biases by up to 96%. This study provides a rigorous physical foundation for the ERM-II mission, preparing it to provide valuable complementary measurements for global climate records in the post-CERES era.