Water Quality Monitoring of Lake Garda Using Multi-temporal Meris Data

The successful launch of MERIS in March 2002 has given a great opportunity to understand the changes of water colour with high temporal and spatial resolutions. In this study, potentials of MERIS sensor were investigated to describe variations of optically active substances of Lake Garda. The basin is located in the Italian sub-alpine lacustrine district, where several other lakes and rivers give the region more than 50% of all Italian freshwater resources. With an area of 368 km and a water volume of 49 km, Lake Garda represents a greatly valuable renewable resource, because the multiple uses of its waters (e.g., drinkable, irrigation, energy, tourism). The size of Lake Garda seems also large enough to be monitored using MERIS. The dataset analysed in this paper includes the MERIS image acquired in Full Resolution mode on 22 July 2003. During the overpass, a large amount of in situ observations were performed, to the aim of image-data processing (mainly atmospheric correction) and validating products (i.e. concentration of chlorophyll). The concentrations values of chlorophyll such as estimated from MERIS were derived applying a band ratio algorithm to atmospherically corrected data. The optimal band ratio (B6/B9) was defined using a semi-analytical bio-optical model parameterised with specific IOPs of Lake Garda. The MERIS-derived chlorophyll values were finally compared with concentrations derived from high spatial resolution fluorescence measurements. The chlorophyll a as it was derived from MERIS was in good agreement with measured values (R=0.76) even if it was slightly underestimated.