page_title: SeaWiFS
section_title: Atmospheric correction
hierarchical_section_title: SeaWiFS / Atmospheric correction
caption_attribution_description: English: NASA SeaWiFS image taken on April 25, 1998, showing the en:coccolithophore en:bloom in the en:Bering Sea. This is not a false-color image: the greenish color is caused by the high concentration of en:phytoplankton. NB Subsequent research suggests that this image, and others from the area showing bright waters early in the year, probably show resedimented particles not an active coccolithophore bloom (Broerse et al. 2003, Continental Shelf Research, 23, 1579-1596).
context_page_description: SeaWIFS was a satellite-borne sensor designed to collect global ocean biological data. Active from September 1997 to December 2010, its primary mission was to quantify chlorophyll produced by marine phytoplankton.
context_section_description: Light reflected from the sub-surface ocean is called water-leaving radiance and is used to estimate chlorophyll concentrations. However, only about 5–10% of light at the top of the atmosphere is from water-leaving radiance. The remainder of light is reflected from the atmosphere and from aerosols within the atmosphere. In order to estimate chlorophyll concentrations this non-water-leaving radiance must be accounted for. Some light reflected from the ocean, such as from whitecaps and sun glint, must also be removed from chlorophyll calculations since they are representative ocean waves or the angle of the sun instead of the subsurface ocean. The process of removing these components is called atmospheric correction.
  A description of the light, or radiance, observed by the satellite's sensor can be more formally expressed by the following radiative transfer equation:
  Where LT(λ) is total radiance at the top of the atmosphere, Lᵣ(λ) is Rayleigh scattering by air molecules, Lₐ(λ) is scattering by aerosols in the absence of air, Lᵣₐ(λ) is interactions between air molecules and aerosols, TLg(λ) is reflections from glint,  t(Lf(λ) is reflections from foam, and LW(λ)) is reflections from the subsurface of the water, or the water-leaving radiance. Others may divide radiance into some slightly different components, though in each case the reflectance parameters must be resolved in order to estimate water-leaving radiance and thus chlorophyll concentrations.
caption: A true color SeaWiFS image of a coccolithophore phytoplankton bloom off of Alaska
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