Retrieval of aerosol optical depths over Hong Kong by using MTSAT-1R

Aerosols suspended in atmosphere have an effect on regional air quality as well as climate change, where monitoring of sources, distribution and transport are very important for studying these topics. There have been numerous studies to retrieve aerosol optical depth (AOD) from geostationary orbit (GEO) satellite. In this study, AOD at 550 nm over Hong Kong is retrieved by using single visible channel of MTSAT-1R. The uncertainty of this algorithm comes mainly from characterizing surface reflectance and the underlying aerosol model. Surface reflectance is estimated from the clear-sky composite with the assumption that there is at least one clear sky condition in the study period and surface conditions do not change for certain periods of time. Aerosol optical properties are obtained from long term observation of AERONET (AErosol ROboric NETwork) at the sites of the Hong Kong Polytechnic University (HPU) and Hok Tsui (HT) for different seasons, which are applied to calculate look-up tables (LUT).

The retrieved AODs are compared with values from MODIS (within 30 minutes) for a year of 2006. The results are compared for the two different aerosol models of HPU and HT, where the results with the HPU model show better correlation than those with the HT. The results show seasonal dependence, with better correlation during spring and fall than summer and winter. Due to relatively high RH condition over Hong Kong, understanding and consideration about RH effects are needed to improve AOD accuracy. Also, improvement in characterizing the aerosol model and cloud masking are expected to decrease the uncertainties further.