Estimation of aerosol optical thickness over land in Chiba area from AVHRR data Original Research Article

In this paper, we describe the application of the texture analysis to the extraction of the aerosol distribution around the Chiba area from NOAA AVHRR data. First, the information on the aerosol distribution is obtained from a satellite image (“the test image”). For this purpose, we use the sea surface (Tokyo bay and the Pacific Ocean) that surrounds the Chiba prefecture. The 6S code is operated under plausible atmospheric conditions, and the value of aerosol optical thickness, τA, is determined by the condition that the calculated total radiance agrees with the observed total radiance. This method is applied to several sites arbitrary chosen on the sea area, and by interpolation, we obtain a “τA image”. Second, we generate a “difference image” by subtracting a “clear image” from the “test image”. The clear image is prepared by applying the atmospheric correction that is based on the radiation transfer calculation using the MODTRAN code to an AVHRR image. The difference image is considered to include the information of the aerosol distribution. By applying the texture analysis to this image, we extract the regions in which the atmospheric features are considered to be uniform (we call them texels). Using this additional information, it is possible to improve the “τA image” so that if both land and sea surfaces are included in a texel, the aerosol optical thickness above the land area is assumed to be the same as that above the sea area. As à whole, the present method makes it possible to extend the method of analyzing atmospheric conditions from satellite data to the land surfaces that are surrounded by water areas.