Service Communautaire d'Information sur la Recherche et le Développement - CORDIS

Catalogue of aerosol optical depth

A semi-operational ATSR aerosol retrieval algorithm has been developed in the framework of CREATE and the ESA project TEMIS. This algorithm is utilized to retrieve aerosol optical depth (AOD) maps over Europe for the year 2000 from available ATSR-2 data.

A cloud-screening algorithm has been automated and implemented as part of the semi-operational ATSR-2 retrieval algorithm. Furthermore, routines were developed to include AERONET sun photometer data of AOD measured within half an hour of the ATSR overpass. AOD maps over Europe for the year 2000 are retrieved from ATSR-2 data, delivered by ESA for the area confined by the latitudinal boundaries (20N, 80N) and the longitudinal boundaries (20W, 40E). Retrieval is done over cloud-free scenes for the 1x1km2 sensor resolution (at nadir). The monthly AOD maps for the European scale are given as a product with a (default) resolution of 10x10km2 (roughly 0.1? x 0.1? over Europe) by means of an automated post-processing step, where the AOD values for the individual ATSR-2 pixels in each 10 x 10km2 area are averaged. This average cannot be considered as monthly averages because the ATSR-2 swath of 512km allows for an overpass over each area in Europe once every third day, at 10:30 in the morning and for many overpasses AOD cannot be retrieved due to the presence of clouds. As a consequence, the data represent a snapshot of the situation during the overpass, and at best each snapshot is available once every third day.

Therefore the monthly maps should be considered as composites providing information on the spatial variation of the occurrence of aerosols and hot spots. A further restriction is the solar zenith angle of maximum 81°, which puts a limit to the amount of available data for the Northern part of Europe, in particular in the winter. The results have been delivered to the CREATE database as maps of AOD at 0.55µm and 0.67µm, together with comparisons with AERONET data for validation. Because part of the work was done in the framework of the ESA project TEMIS, and the TEMIS webpage will be maintained for at least several years with likely continuation by the ESA GMES Service Element (GSE) PROMOTE, the results have also been provided to the TEMIS web pages ( where they are available to the users. The TEMIS web site is linked to the CREATE web site ( Single frames or maps over specific areas can be produced for a single overpass with high spatial resolution. This product is useful for application on a local scale, such as urban pollution monitoring or source assessment by inverse modelling.

Much effort has been put into developing routines for providing the data for applications that require other spatial resolutions than the default 10x10 km2 or the high resolution 1x1km2 products, such as for the intercomparison of aerosol model results, ground-based and space-based observations. This exercise required binning the high-resolution AOD values in cells of 1? x 1?. Another application is the assimilation of ATSR-2 AOD data in regional and global models in the FP5 GMES targeted project DAEDALUS that has been coupled to CREATE on request of the EU Commission.

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Reported by

Physics and Electronics Laboratory, PO Box 96864
2509 JG The Hague