Modification to the atmospheric correction of SeaWiFS ocean colour images over turbid waters

The successful exploitation of remotely sensed observations of water colour in the coastal zone requires atmospheric correction methods that can determine water reflectance from top-of-atmosphere radiometric measurements over waters containing significant non-phytoplanktonic particulate material. These so-called Case II waters often have significant water leaving radiance at near infra-red (NIR) wavelengths which invalidates conventional “dark pixel” atmospheric correction procedures, including those using the Siegel-type NIR iterative-correction scheme. A coupled ocean-atmosphere model is described that solves for water-leaving radiance and atmospheric path radiance over Case II turbid waters from measurements by the NASA ocean colour satellite sensor, SeaWiFS. The theoretical basis of this model is described, together with its implementation within the SeaWiFS data processing system, SeaDAS. The resulting products are validated using five test images of European waters, where the modified atmospheric correction leads to significant increases in normalised water leaving-radiances across the whole spectrum and to fewer negative water leaving radiances.