Retrieving aerosol optical depth using visible and mid-IR channels from geostationary satellite MTSAT-1R

An algorithm to retrieve aerosol optical depth (AOD) from a geostationary earth orbit (GEO) satellite by using visible and mid-infrared (mid-IR) channels is presented. This algorithm allows us to monitor transport of aerosols in higher temporal resolution from space in East Asia where both natural and anthropogenic aerosols exist all year round. The AOD is retrieved from two channels of 0.67 and 3.7 μm on board a GEO satellite, MTSAT-1R, by using the look up table (LUT) approach. To overcome limitations of previous single visible channel algorithms of GEO satellites in estimating surface reflectance based on clear-sky assumptions over a 30 day period, the possibility of using a mid-IR channel at 3.7 μm was investigated. With the aid of the mid-IR channel over a restricted surface area, surface reflectance was better characterized; this leads to smaller errors in the AODs. The application of a mid-IR channel in retrieving surface reflectance shows potential in retrieving more accurate AODs from GEO satellites and is complementary to the clear-sky composite method. The limitations in applying the mid-IR channel and its dependency on surface temperatures should be treated appropriately in order to avoid errors in AOD retrieval.