Adjacency Effects and Bio-optical Model Regionalisation: Meris Data to Assess Lake Water Quality in the Subalpine Ecoregion

This study is part of ongoing research efforts aimed to developing Earth Observation (EO) strategies towards the implementation of the Water Framework Directive (WFD), ensuring systematic monitoring of water quality in the largest lakes of the Subalpine ecoregion (northern Italy). To the aim the Medium Resolution Imaging Spectrometer (MERIS) Full resolution (FR) data offer an excellent choice. Unfortunately MERIS L2P water products available for the Subalpine lakes partially fail in describing the concentrations of water quality parameters. To overcome these limitations MERIS L1P data were used in this study. Top-of-atmosphere radiances were converted into remote sensing reflectances using the MODTRAN-based atmospheric correction code c-WOMBAT-c, that is complemented with a correction for the adjacency effects. A bio-optical model-driven optimisation technique was then used to convert remote sensing reflectance into water quality parameters from a MERIS FR timeseries acquired in 2005. MERIS-derived chlorophyll-a concentrations were comparable to in situ measurements performed in Lake Garda (r=0.98; RMSE=0.88 mgm; RMSE=26%). Convincingly trends were also derived for other lakes (i.e., Maggiore, Como and Iseo) belonging to the same ecoregion.