Retrieval of aerosol optical depth over ocean: Gradient technique

The presence of aerosol in the atmospheric plays a significant role in the earth´s radiation budget through radiative forcing and chemical perturbations. They scatter solar radiation back to space, absorb solar and terrestrial radiation, and act as cloud condensation nuclei, influencing cloud/precipitation processes and changing cloud reflectivity. Estimating aerosol properties is also one of the first steps in generating high-level land and ocean surface products from satellite observations. The study of atmospheric aerosols is an important element to understand the earth´s solar radiation budget, water cycle balance, and climate change dynamics. In this paper, a simple method to estimate the aerosol optical depth (AOD) over ocean is proposed. The method is based on the gradient of the line connecting the 0.47, 1.24, 1.64 and 2.14 μm. The line gradients are decreased over the high aerosol contribution area and increased over low aerosol contribution area. The comparison of the gradient line and AOD map distributed by MODIS ocean color team are in high correlation (R>;0.9). The AOD map from the applications of the algorithm was constructed. The sample result of AOD map from several MODIS datasets acquired over the Gulf of Martaban is presented.