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Observations of the largest Italian lakes from MERIS

Claudia Giardino(1), Mariano Bresciani(1), Vittorio E Brando(2) and Arnold G Dekker(2)

(1) Consiglio Nazionale delle Ricerche - IREA, Via Bassini 15, 20133 Milano, Italy
(2) CSIRO - Land and Water, GPO Box 1666, ACT 2601 Canberra, Australia


With the successful launch of Envisat-1 in March 2002 and the approval of MELINOS project (ESA-AO-553), we have been starting to investigate the performances of MERIS Full Resolution data to map water quality in lake waters and to describe temporal trends. The research activities have been firstly focused on the largest Italian lake: Lake Garda (surface of 368 km2), located in the Sub-alpine region in northern Italy, where some previous research activities provided a good description on Specific Inherent Optical Properties (SIOPs) of the lake. The MODTRAN based atmospheric correction tool c-WOMBAT-c has been adopted to convert the top-of-atmosphere radiances into remote sensing reflectance, by also correcting for the adjacency effects, demonstrated they were strongly influencing MERIS measurements in the narrowest portion of the lake. MERIS reflectances from 2003 to 2007 were inverted using a bio-optical model calibrated with the SIOPs of the lake providing chlorophyll-a concentrations within a reasonably accuracy (R2=0.8). Based on these results, the methodology has been applied to describe temporal trends in the other main lakes of the Sub-alpine region (i.e., Maggiore, Como and Iseo), whose characterisation, in terms of SIOPs, is still in progress. More recently, to respond to the needs of the regional agency for the environmental protection, Lake Trasimeno has been included as study area of our research activities. The lake, located in central Italy in the Appenine region, with a surface area of 128 km2 is the fourth largest lake in Italy, resulting slighting less than Lake Como. With respect to the Sub-alpine lakes, Lake Trasimeno is definitely shallower (its average depth is of 4 m, while it is more than 100 m for Sub-alpine lakes) and in a worst quality status (meso-eutrophic level; Secchi disk depth around 1-1.5 m). Preliminary results on optical characterisation of Lake Trasimeno and its implication on bio-optical model regionalisation, as well as mapping of MERIS-derived water quality products, will be presented in this study by considering the experience achieved in studying Sub-alpine lakes. We expect that these results, which have been also driven by end-users needs, will contribute to implement the WFD (Directive 2000/60/EC) for the largest lakes in Italy by developing Earth Observation strategies towards a systematic water quality monitoring.


Workshop presentation

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