How many independent quantities can be extracted from ocean color?

Abstract

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