Full of Colors: the first derivation of Orthogonal Components of Water and its implications for aquatic studies

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Abstract
Aquatic systems exhibit diverse and complex optical properties caused by mixtures of optically active constituents, and significant efforts have been made to characterize these constituents from satellite optical data. However, a fundamental challenge remains in translating spectral information into distinct, reduced, and intuitive representations for aquatic science applications. In this study, we introduce a new Orthogonal Components of Water (OCW) approach that summarizes the full visible-spectrum into three individual components, named Brightness, Greenness, and Blueness, to enhance the interpretation of spectral composition across aquatic systems. The OCW approach was developed using a rigorous selection of endmember spectra from a global hyperspectral dataset (n=12,867) to implement the Gram–Schmidt orthogonalization technique, and then per-component coefficients were derived for seven satellite missions, including PACE-OCI, Aqua/Terra MODIS, JPSS1/JPSS2 VIIRS, Sentinel-3 OLCI, Sentinel-2 MSI, Landsat8/9 OLI, and PlanetScope SuperDove. OCW applications were evaluated at both regional and global scales, and the results confirmed the reliability of each OCW in reducing spectral dimensionality while preserving the interpretability of dominant optical regimes. OCW Brightness showed a strong relationship with total suspended solids and non-algal particles, with Pearson’s correlation coefficients (r) ranging from approximately +0.46 to +0.77. OCW Greenness was highly correlated with phytoplankton features (r of +0.79 to +0.83), while OCW Blueness exhibited a negative correlation with increasing concentrations of optically relevant biogeochemical parameters (r values ranging from +0.08 to -0.84), and represents predominantly clear-water conditions. Together, these results confirm that OCWs are rich representations of aquatic spectral composition for both multispectral and hyperspectral applications.

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