Practical application of the ``turbid water'' flag in ocean color imagery: Interference with sun-glint contaminated pixels in open ocean
Résumé
A simple method to identify turbid, sediment-loaded, waters within satellite ocean color imageries was recently proposed (A. Morel and S. Belanger, Remote Sensing of Environment, 102, (2006), 237-249). Systematic application of this method to the level-3 composites obtained from three ocean color sensors shows that the ``turbid'' flag is often raised in the open ocean, especially in the sub-tropical oligotrophic gyres, where turbidity is unlikely. In addition these flagged zones migrate with season, and clearly follow the sun declination course. The combination of low chlorophyll waters with a residual sun-glint is at the origin of this artifact. Simple approaches for eliminating such a misleading detection are proposed. The identification and elimination of the bias are also needed in particular for an unambiguous detection of the presence of calcite (coccolithophores) in open waters. (C) 2008 Published by Elsevier Inc.