Global Distribution of Case-1 Waters: An Analysis from SeaWiFS Measurements

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Case-1, Case-2, Ocean color, Remote sensing, Bio-optical model

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“Case-1” has been a term frequently used to characterize water type since the seventies. However, the distribution of Case-1 waters in global scale has been vague, though open ocean waters are often referred to as Case-1 in the literature. In this study, based on recent bio-optical models for Case-1 waters, an inclusive and quantitative Case-1 criterion for remote sensing applications is developed. The criterion allows Case-1 waters to have about two-fold variations of non-pigment absorption and particle backscattering around their exact Case-1 values, allowing a large range of waters to be classified as Case-1. Even so, application of this criterion to ocean color data from the SeaWiFS satellite sensor suggests that Case-1 waters occupy only about 60% of the global ocean surface. Regionally, more Case-1 waters are found in the southern hemisphere than in the northern hemisphere, and most Indian Ocean waters are found to be Case-1. The Case-1 percentage and spatial distribution change with season, and with the boundaries chosen in the criterion. Nevertheless, this study for the first time provides a quantitative and geographical perspective of Case-1 waters in global scale, and further demonstrates that many open ocean waters are not necessarily Case-1.

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Citation / Publisher Attribution

Remote Sensing of Environment, v. 101, issue 2, p. 270-276