57 Geocarto International, Vol. 19, No. 4, December 2004 E-mail: geocarto@geocarto.com Published by Geocarto International Centre, G.P.O. Box 4122, Hong Kong. Website: http://www.geocarto.com Introduction Recent studies worldwide have revealed a relation between urban air pollution, particularly fine aerosols, and human health (Anderson et al., 1996; Seaton et al., 1995; McMichael et al., 1996; Katsouyanni et al.; 1996; Pope et al., 1995; Saldina et al., 1995). This, in turn, has created a pressing request from both environmental scientists and decision- makers for spatial, timely and comparable information on air pollution, urban aerosol and associated indicators (WHO, 2000). The exploitation of Earth Observation (EO) satellite Estimation and Mapping of Aerosol Optical Thickness over the City of Brescia - Italy Using Diachronic and Multiangle SPOT-1, SPOT-2 and SPOT-4 Imagery Nikolaos A. Soulakellis Department of Geography, University of the Aegean 81100 Mytilini, Greece E-mail: n.soulakellis@aegean.gr Nicolaos I. Sifakis Institute for Space Applications and Remote Sensing National Observatory of Athens, Greece Maria Tombrou Department of Physics National and Kapodistrian University of Athens, Greece Denis Sarigiannis European Commission, Joint Research Centre Square de Meeus 8, Brussels B-1050, Belgium Klaus Schaefer Institut für Meteorologic und Klimaforschung Atmosphärische Umweltforschung Forschungszentrum Karlsruhe GmbH, Garmisch-Partenkirchen, Germany Abstract In this paper we process diachronic SPOT satellite images acquired with different viewing angles in order to assess the aerosol optical thickness (AOT) spatial distribution over Brescia. This urban area, located in Northern Italy, is subject to frequent visibility-reducing smog episodes. AOT was calculated by using the Differential Textural Analysis (DTA) code on a satellite data series consisting by one pollution-free and various pollution-loaded SPOT images. The resulting maps showed the horizontal distribution of AOT with a resolution of 500 metres. These maps can be readily integrated with the results obtained by mesoscale modelling, ground measurements, and respond to local scale application requirements. Satellite AOT retrieval compared successfully with available AOT ground-based measurements and with pollution measurements in the ambient air. In this study the use of diachronic multiangle SPOT imagery allowed us to analyse the effect of the viewing angle variation on AOT retrieval accuracy based on the contrast reduction method. images could provide us with relevant information (Kaufman et al., 2002) especially when acquired over urban areas and during air pollution episodes (Sarigiannis et al, 2003; Sifakis et al., 2003). Particularly high spatial resolution (HSR) EO sensors can sense the optical atmospheric effects engendered to the recorded signal by aerosols through scattering and absorption processes, and with resolutions satisfying the requirements of urban scale studies (Sifakis and Soulakellis, 1996). Various algorithms pertained to urban air pollution assessment by means of HSR satellite imagery have already been developed