Improved aerosol optical depth and particle size index from satellite detected radiance.

Abstract

An algorithm that extracts aerosol optical depth and particle size index from satellite observations of upwelling radiance over clear ocean areas was modified and studied. In order to examine the algorithm's performance on a regional scale, a previously analyzed data set, retrieved by the NOAA-9 AVHRR sensor, was reprocessed. The area of the study was in the central Pacific Ocean during the RITS-88 cruise from 7 April to 5 May 1988. The results were compared to those of the earlier study and used to investigate changes caused by modifications to the algorithm. One significant modification was to account for the absorption of column water vapor in the calculations. In addition, the correlation between aerosol optical depth and the two-term Henyey-Greenstein phase function was investigated by normalizing measured radiance values. The results compared well with the earlier study and supported the modifications to the algorithm. Based on this study, aerosol optical depth was shown to be correlated to the Henyey-Greenstein phase function. This knowledge helped in formulating improvements to the phase function. It was concluded that satellite imaging and processing on a regional scale is a useful way to study marine aerosols, that results can be improved by considering the effects of atmospheric water vapor absorption and other modifications to the calculations, and that there is room for improvement to the two-term Henyey-Greenstein phase function.