Comparison of MODIS aerosol optical depth retrievals with ground-based measurements in the tropics

Aerosols are small particles suspended in the atmosphere. They may have profound effects on human health. Their effects on the physical environment can also be of importance as they have the ability to both scatter and absorb incident solar radiation. The ability of aerosols to deplete solar radiation can be quantified in terms of aerosol optical depth (AOD). AOD can be retrieved from the MODIS satellite. However, AOD from this satellite has a wide range of uncertainty, depending on environments and climatic zones. In this work, AOD retrieved from MODIS was compared to that obtained from ground-based measurements at four sites in the tropical environment of Thailand. These are Chiang Mai (18.78 °N, 98.98 °E), Ubon Ratchathani (15.25 °N, 104.87 °E), Nakhon Pathom (13.82 °N, 100.04 °E) and Songkhla (7.2 °N, 100.60 °E). AOD at these sites was measured by using Cimel sunphotometers. The AOD data from these sites over a period of 2-5 years was used in the comparison. It was found that the discrepancy in terms of root mean squared difference between the daily AOD retrieved from MODIS and that of the ground-based measurements was in the range of 33.8%-53.7%.