Estimating Aerosol Optical Depth Over the Broader Greek Area from MODIS Satellite

Abstract

A first-to-date comprehensive climatological aspect of the regime of aerosol loading over the entire broader Greek region (19°E–30°E and 34°N–43°N) is obtained using pixel-level (50 km × 50 km) monthly aerosol optical depth (AOD) products derived from raw Level-2 (10 km × 10 km) MODIS-Terra AOD data at 550 nm. The AOD climatology (for the 8-year period from March 2000 to February 2008) indicates that the study region is significantly loaded by aerosols (mean regional AOD equal to 0.196 ± 0.030 on an annual basis, with values ranging from 0.126 up to 0.382 at pixel level). It is also found that our high-resolution AOD data can reveal spatial patterns that are not evident in studies based on lower resolution data. There is a distinct longitudinal gradient of AODs, with higher values in the eastern than western part of the Greek peninsula. There is also a strong latitudinal gradient with decreasing values from south to north attributed to the presence of the Sahara Desert in northern Africa. The annual AOD cycle presents double maximum values, in spring and summer, and minimum ones in winter. There is also a remarkable year-by-year variability of AOD levels, especially as to their maxima, influenced by varying transport of desert dust, from the south, or biomass burning aerosols, from the north, to the region under prevailing favorable synoptic conditions. In this work, the processing, consisting in averaging over space and time, is done applying/testing five different criteria varying in their flexibility/severity in both spatial and temporal data availability. The criteria selection affects the magnitude of computed regional mean AOD value modifying it by up to 19 %, although the patterns of geographical distribution of AOD and its intra-annual variability do not change drastically.