Atmospheric correction of ocean color imagery in the Earth Observing System era

Sensors that can be used for the observation of ocean color in NASA's Earth Observing System era (SeaWiFS, MODIS, and MISR) have been designed with 2-4 times the radiometric sensitivity of the proof-of-concept ocean color instrument CZCS (coastal zone color scanner). To realize an improvement in the retrieval of biologically important ocean parameters, e.g., the concentration of the photosynthetic pigment chlorophyll a, from this increased sensitivity, significantly better atmospheric correction than was applied to CZCS is required. Atmospheric correction improvement necessitates the inclusion of the effects of multiple scattering, which are strongly dependent on the aerosol size distribution, concentration, and absorption properties. We review the basic concepts of atmospheric correction over the oceans and provide the details of the algorithms currently being developed for SeaWiFS, MODIS, and MISR. An alternate correction algorithm that could be of significant value in the coastal zone is described for MISR. Related issues such as the influence of aerosol vertical structure in the troposphere, polarization of the light field, sea surface roughness, and oceanic whitecaps on the sea surface are evaluated and plans for their inclusion in the algorithm are described. Unresolved issues, such as the presence of stratospheric aerosol, the appropriateness of the aerosol models used in the assessment of multiple scattering, and the identification of, and difficulties associated with the correction for, the presence of absorbing aerosols, e.g., urban pollution or mineral dust, are identified, and suggestions are provided for their resolution.