Relationship between apparent optical properties and photosynthetic pigments in the sub-alpine Lake Iseo

The aim of the present study was the evaluation of methods for estimating t he content of bio-physical parameters in lake water on the basis of spectra l reflectance measured above water surface, in particular the estimation of chlorophyll-a (chl-a) concentrations. Data sets considered refer to some s ampling point located in the sub-alpine meso-eutrophic Lake Iseo, surveyed six times over the period March-July and once in November 1998, as these mo nths were very important for the characterization of the springtime algal b loom, which affect the lake waters yearly. At each point station, limnologi cal observations (chlorophyll, total suspended solids. Secchi disk depth) w ere conducted simultaneously with optical measurements. The latter consiste d of water leaving radiance measured by means of a spectroradiometer above the water surface: moreover, a standard reflector radiance was also measure d to obtain the water reflectance. Reflectance spectra were transformed acc ording to two well-documented models and correlated to water quality parame ters, to investigate their performances as retrieval algorithms under diffe rent conditions and referring to different analytical methods. Results outl ine the sensitivity of the models to chl-a concentrations, different phytop lankton composition, and the sampling depth. (C) 2001 Elsevier Science B.V. All rights reserved.