Reconstructing Missing Spectral Bands for Seamless Continuity Between GOCI and GOCI-II

Establishing data continuity across satellite missions is essential for multi-decadal ocean color time-series. This study presents an integration framework to achieve radiometric harmonization and spectral continuity between the First and Second Geostationary Ocean Color Imagers (GOCI and GOCI-II) over the East China Sea. Using collocated observations during their mission overlap period, a two-step transformation scheme was established. First, systematic calibration offsets across six overlapping bands (412–680 nm) were eliminated by harmonizing GOCI to the GOCI-II via ordinary least-squares regression, bringing mean bias values near zeros (R2 > 0.95 and relative RMSD ≈ 12–13% in mid-visible bands). Second, GOCI remote sensing reflectance (Rrs) was expanded to reconstruct three GOCI-II-specific missing spectral bands (510, 620, and 709 nm) using two independent approaches: the physics-based Quasi-Analytical Algorithm (QAA) and Trust Region Reflective (TRR) optimization. Comparative validation demonstrated that the TRR model consistently outperformed QAA across dynamic coastal gradients. TRR achieved high spectral fidelity while suppressing coastal inversion errors. Furthermore, regional spectral curves verified that the harmonized and TRR-derived GOCI Rrs closely converged with GOCI-II Rrs across moderately turbid, highly turbid, and clear offshore waters. This framework verifies the feasibility of constructing a seamless geostationary ocean color database spanning GOCI and GOCI-II, establishing a solid foundation for long-term marine monitoring and future missions like GOCI-III.