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Ocean Colour (MERIS/MODIS/SeaWiFS) and SST (AATSR/MODIS/AVHRR) inter-sensor comparison for the Azores region

Ana Martins(1), Ana Mendonça(1), Miguel Figueiredo(2) and Igor Bashmachnikov(2)

(1) University of the Azores, Cais de Santa Cruz, 9901-862 Horta, Faial, Azores, Portugal
(2) IMAR-Instituto do Mar, University of the Azores, 9901-862 Horta, Faial, Azores, Portugal


The performance of three Ocean Colour (OC)sensors (MERIS, MODIS, and SeaWiFS) and three SST sensors (AATSR, MODIS, and AVHRR) are inter-compared for the Azores region, under the framework of project OPALINA: PDCTE/CTA/49965/2003. SeaWiFS and AVHRR data were obtained from the HRPT "HAZO" station in the Azores. MODIS data were obtained from NASA and MERIS and AATSR data were obtained from ESA. All satellite data were processed using the HAZO system developed at the Department of Oceanography and Fisheries at the University of the Azores (DOP/UAç). The monthly means and other statistical data were obtained for all sensors from January 2004 up to December 2005 and compared among them. Ocean Colour sensors show clear seasonal variability with highest (up to 0.5 chlorophyll a mg m-3) pigment concentration during spring and lowest (about 0.08 chlorophyll a mg m-3) during summertime. Best agreement is found between MERIS and MODIS OC sensors, while SeaWiFS tends to overestimate the monthly means and shows the highest data variability. Thermal infrared sensors also show evident seasonality with highest sea surface temperature values (about 24 C) observed during summertime and lowest (15 C) during winter. Best agreement is found between AATSR and AVHRR, with a slight overestimation of the first towards the latter. However, MODIS shows clear monthly mean SST values underestimation and the highest variability. This is the first oceanographic study that uses ENVISAT data for the Azores region. It is important that future studies address more specific OC and SST inter-sensor comparisons in order to implement satellite regional algorithms for this region.


Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry