How many independent quantities can be extracted from ocean color?

Products derived from remote sensing reflectances (RrsλðÞ), for example, chlorophyll, phytoplankton carbon, euphotic depth, or particle size, are widely used in oceanography. Problematically, RrsλðÞ may have fewer degrees of freedom (DoF) than measured wavebands or derived products. Here, we show that a global sea surface hyperspectral RrsλðÞ dataset has DoF=4. MODIS-like multispectral equivalent in situ data also have DoF=4, while their SeaWiFS equivalent has DoF=3. Both multispectral-equivalent datasets predict individual hyperspectral wavelengths’ RrsλðÞ within nominal uncertainties. Remotely sensed climatological multi-spectral RrsλðÞ have DoF=2, as information is lost by atmospheric correction, shifting to larger spatiotemporal scales, and/or more open-ocean measurements, but suites of RrsλðÞ -derived products have DoF=1. These results suggest that remote sensing products based on existing satellites’ RrsλðÞ are not independent and should not be treated as such, that existing RrsλðÞ measurements hold unutilized information, and that future multi- or especially hyper-spectral algorithms must rigorously consider correlations between RrsλðÞ wavebands.