A method to retrieve total aerosol optical depth from satellite observations of cloud-free scenes over oceans with high spatial resolution (~1 DEG) and instantaneous temporal resolution is described and evaluated. The observed radiance is treated as the linear sum of contributions to path radiance by different scattering processes in the atmosphere-ocean system. This treatment allows examination of errors in the retrieved aerosol optical depth contributed by each process or approximation. The random and systematic errors in the measured radiance correspond to errors of 0.05 and 0.04 in the retrieved aerosol optical depth, respectively. The largest relative errors and biases are due to the radiative transfer approximations (30%) and the aerosol microphysical optical properties (25%), the latter varying systematically with latitude and season. This method is applied to Advanced Very High Resolution Radiometer (AVHRR) Global Area Coverage (GAC) data and example maps of aerosol optical depth are presented for specific dates in July and October 1986. The aerosol optical depth derived from the satellite data is suitable for examining large aerosol signatures by instantaneous comparison of the amplitude and location of aerosol plumes with model predictions based on meteorological conditions at and preceding the time of observation.
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