Intercomparison of desert dust optical depth from satellite measurements

This work provides a comparison of satellite retrievalsof Saharan desert dust aerosol optical depth (AOD)during a strong dust event through March 2006. In this event,a large dust plume was transported over desert, vegetated,and ocean surfaces. The aim is to identify the differencesbetween current datasets. The satellite instruments consideredare AATSR, AIRS, MERIS, MISR, MODIS, OMI,POLDER, and SEVIRI. An interesting aspect is that the differentalgorithms make use of different instrument characteristicsto obtain retrievals over bright surfaces. These includemulti-angle approaches (MISR, AATSR), polarisationmeasurements (POLDER), single-view approaches using solarwavelengths (OMI, MODIS), and the thermal infraredspectral region (SEVIRI, AIRS). Differences between instruments,together with the comparison of different retrievalalgorithms applied to measurements from the same instrument,provide a unique insight into the performance andcharacteristics of the various techniques employed. As wellas the intercomparison between different satellite products,the AODs have also been compared to co-located AERONETdata. Despite the fact that the agreement between satellite andAERONET AODs is reasonably good for all of the datasets,there are significant differences between them when comparedto each other, especially over land. These differencesare partially due to differences in the algorithms, such as assumptionsabout aerosol model and surface properties. However,in this comparison of spatially and temporally averageddata, it is important to note that differences in sampling, relatedto the actual footprint of each instrument on the heterogeneousaerosol field, cloud identification and the qualitycontrol flags of each dataset can be an important issue