Aerosol Optical Depth of MODIS Imagery over Bright Coastal Water: A Regression Technique

The contribution of sediment and bottom reflectance in the MODIS imagery over bright coastal water contaminate visible and near infrared channels. This contribution leads to the saturation in the ocean color channels and error in the MODIS derived product over that areas. The saturation in the ocean color channels lead to no aerosol optical depth (AOD) retrieved by MODIS algorithm over very turbid areas. The sediment contributions will increase the reflectance in the visible and near infrared channel that is used in the MODIS aerosol algorithm. This area is then masked using sediment masking algorithm. In this paper, a simple method to estimate the AOD over bright coastal water with high sediment and bottom reflectance contributions is proposed. The first seven MODIS solar channels centered at 0.47, 0.55, 0.66, 0.86, 1.24, 1.64 and 2.13 µm, originally designed for remote sensing over land and cloud properties have been utilized in this study. The algorithm is based on the excess reflectance at 0.55, 0.66 and 0.87 µm wavelength using the power law model that can be associated to the presence of sediment. The excess value of the reflectance is discarded, to obtain the atmospheric contribution in the data. Aerosol contribution over bright coastal water areas is then compared with AOD of 0.869 µm using regression technique. This study shows that the AOD and aerosol retrieved are in high correlation with R is greater than 0.90. The AOD map from the applications of the algorithm were constructed and extrapolated for the saturated channels areas. The sample result of AOD map from several MODIS datasets acquired over the Gulf of Martaban is presented.