Variability in near-surface particulate absorption spectra: What can a satellite ocean color imager see?

Abstract

An extensive database of -400 in situ particulate absorption spectra [a,(X)] is analyzed to assess the potential of using ocean color imagers to examine variability in the structure of the near-surface ocean planktonic ecosystem. This application of a,(X) data is appropriate, as particulate absorption variations are the dominant source of ocean color variation and are attributable to changes in the phytoplankton community structure. Empirical orthogonal function (EOF') analyses are used to estimate the contribution of each statistical mode to the total variance. The EOF analyses showed that > 99% of the variance found in the a,(X) data set can be simply attributed to the total amount of particulate material. When this source of variability is removed, two significant modes of variability can be identified which comprise 79 and 18% of the normalized variance. These modes are interpreted as representing the relative contribution of chlorophyll-containing biomass and detrital materials, verifying the use of two-component phytoplankton-detritus models to partition a,(X). Only a small amount of the total a,(X) variability (~0.5% of the total) can be attributed to absorption features caused by accessory pigment groups. Thus, variability in a,(X) is almost entirely associated with the quantity of the absorbing materials rather than their spectral quality (or normalized spectral shape). These results suggest that remotely sensed ocean color spectra will reflect only three statistically significant components: the total amount of particulate material, the relative amounts of chlorophyll-containing biomass, and detrital materials. For most typical conditions it is unlikely that robust global algorithms for determining particular phytoplankton groups can be developed from remotely sensed ocean color spectra.

A Consumer's Guide to Satellite Remote Sensing of Multiple Phytoplankton Groups in the Global Ocean

“…A limitation of absorptionbased approaches is that they are sensitive to physiological variability associated with light and nutrient histories and these are likely to be of more influence when normalized quantities are used. Furthermore, small changes in the spectral shape of phytoplankton absorption can be difficult to retrieve from ocean-color (Garver et al, 1994;Wang et al, 2005), such that identifying and distinguishing different PFTs may not always be successful. Problems can also occur when trying to discriminate different phytoplankton groups with similar absorption signatures.…”

Modes and mechanisms of ocean color variability in the Santa Barbara Channel

“…Comparatively little is known about the backscattering spectrum in case II waters [e.g., Gordon and Morel, 1983] …”

“…Determinations of Rrs(0+,X) provide the link between satellite ocean color imagery and in situ concentrations of optically significant constituents through knowledge of the inherent optical properties (lOP) of the water column [e.g., Gordon et al, 1975;Morel and Prieur, 1977]. R,(0+,X) is defined as the ratio of water-leaving, upwelling radiance, Lu(O+,X), to the incident downwelling irradiance, E•0+,X), or …”

Relationships between the surface concentration of particulate organic carbon and optical properties in the eastern South Pacific and eastern Atlantic Oceans

“…Relationships between ocean reflectance and SPM have also been investigated for the purpose of estimating SPM from remote sensing (Gordon and Morel, 1983;Stumpf and Pennock, 1989;Doxaran et al, 2002).…”