Monitoring chlorophyll-a with remote sensing techniques in the Tagus Estuary

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Gestão e Sistemas Ambientais

Estuaries are transitional ecosystems with high temporal and spatial variability and suffer high anthropogenic pressures. At the present there is a major challenge to monitor these systems in a robust, frequent, systematic and accurate fashion. With the implementation of the Water Framework Directive (WFD), the EU Member States must monitor regularly the most relevant physical and biological parameters. Estuarine information is attained using in-situ samples, model analysis and/or remote sensing data. This work assessed the applicability and accuracy of chlorophyll-a products from the MODIS sensor in the Tagus estuary, comparing them (2000-2002) with simulations of an ecological model, the EcoWin2000. The latter was previously calibrated (1998 & 1999) and validated(2000). It is proposed a conceptual and methodological framework for future monitoring of the estuary using remote sensing data. In a first stage, in the year 2000, typical Case 1 algorithms were pre-assessed and Case 2 algorithms were regionally calibrated. The GSM and Clark algorithms had the best performances, with errors of approximately of 1.1 μg chl-a l-1 (or 20%) and correlations ranging 0.4-0.5. During calibration, the ratio R678/R551 had a good correlation (r = 0.83) and low errors (~1μg chl-a l-1). Its evaluation in 2002, showed low and sometimes negative correlations, with errors of about 2 μg chl-a l-1. In agreement with the preliminary assessment,in 2002, the GSM algorithm had the best correlation (r~0.50) and errors of approximately 0.8μg chl-a l-1. The reliability of remote sensing is higher in the Spring and Summer, and spatially, in the wider mid estuary sections. Although remote sensing needs extensive further development, it was proven to be a reliable tool with several advantages for systematic chl-a monitoring in the Tagus estuary. Specifically, it is a tool with high to assist the EU Member States to accomplish the WFD objectives.