Spectral Response of Remote Sensing Reflectance to Variation in CDOM, Phytoplankton, and Mineral Particles in Baltic Waters

Remote sensing reflectance (Rrs) in optically complex waters is controlled by the combined effects of phytoplankton, colored dissolved organic matter (CDOM), and suspended mineral particles. In the Baltic Sea, strong CDOM absorption and variable particle loads complicate the interpretation of ocean color signals and the retrieval of biogeochemical properties. In this study, we investigate the individual and combined influence of these optically significant constituents on Rrs using a set of HydroLight radiative transfer simulations representing typical Baltic Sea conditions. A wide range of chlorophyll-a (0.25–10 mg·m−3), CDOM absorption (0.5–15 m−1), and particulate inorganic matter (0.04–4 g·m−3) was considered. To quantify the influence of each component, a spectral response function was applied, defined as the change in Rrs relative to a normalized perturbation of each input parameter. This approach preserves information about the magnitude of the reflectance signal and allows direct comparison of the impact of different constituents across the visible spectrum. The spectral response analysis reveals that the relative influence of each constituent varies with wavelength and environmental conditions, highlighting the limitations of single-band or ratio-based algorithms in optically complex waters. These findings provide a quantitative framework for interpreting spectral variability of Rrs in the Baltic Sea and other optically complex water basins, support the development of more robust bio-optical algorithms for Case 2 waters. Similar spectral response analysis can be conducted in other water basins in order to quantify combined constituent-specific effects on Rrs.