Global Two-Channel AVHRR Retrievals of Aerosol Properties over the Ocean for the Period ofNOAA-9Observations and Preliminary Retrievals UsingNOAA-7andNOAA-11Data

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Abstract
Described is an improved algorithm that uses channel 1 and 2 radiances of the Advanced Very High Resolution Radiometer (AVHRR) to retrieve the aerosol optical thickness and Ångström exponent over the ocean. Specifically discussed are recent changes in the algorithm as well as the results of a sensitivity study analyzing the effect of several sources of retrieval errors not addressed previously. Uncertainties in the AVHRR radiance calibration (particularly in the deep-space count value) may be among the major factors potentially limiting the retrieval accuracy. A change by one digital count may lead to a 50% change in the aerosol optical thickness and a change of 0.4 in the Ångström exponent. On the other hand, the performance of two-channel algorithms weakly depends on a specific choice of the aerosol size distribution function with less than 10% changes in the optical thickness resulting from replacing a power law with a bimodal modified lognormal distribution. The updated algorithm is applied t... Abstract Described is an improved algorithm that uses channel 1 and 2 radiances of the Advanced Very High Resolution Radiometer (AVHRR) to retrieve the aerosol optical thickness and Ångström exponent over the ocean. Specifically discussed are recent changes in the algorithm as well as the results of a sensitivity study analyzing the effect of several sources of retrieval errors not addressed previously. Uncertainties in the AVHRR radiance calibration (particularly in the deep-space count value) may be among the major factors potentially limiting the retrieval accuracy. A change by one digital count may lead to a 50% change in the aerosol optical thickness and a change of 0.4 in the Ångström exponent. On the other hand, the performance of two-channel algorithms weakly depends on a specific choice of the aerosol size distribution function with less than 10% changes in the optical thickness resulting from replacing a power law with a bimodal modified lognormal distribution. The updated algorithm is applied t...