DETERMINATION OF SAHARAN DUST RADIANCE AND CHLOROPHYLL FROM CZCS IMAGERY

An atmospheric correction algorithm is derived for oceanic areas of low chlorophyll a plus phaeophytin a concentrations (<C> less-than-or-equal-to 0.25 mg/m3). The algorithm simultaneously corrects for the radiance effects of two different aerosol types observed in coastal zone color scanner (CZCS) imagery. The algorithm, called the two-component method, is applied to data from a time series of CZCS orbits during which both Saharan dust and a bluish haze were present. The method is evaluated by comparing the ocean chlorophyll concentrations after atmospheric correction to those measured in situ and to those determined by single-component methods from CZCS imagery. Reasonable agreement is found between the chlorophyll values estimated by the two-component method and in situ values, and the derived chlorophyll values for a Sargasso Sea region varied by less than 6% during a major influx of Saharan dust to the region. Aerosol and chlorophyll fields appeared confounded in imagery derived using single-component methods when multiple aerosol types were present, but no confounding was observed for imagery generated by the two-component method. The time series of aerosol radiance values due to Saharan dust was consistent with the changes in dust concentration and particle size measurements from an adjacent aerosol collection site on the Florida coast.