MEASUREMENTS AND SIGNIFICANCE OF BIOOPTICAL PARAMETERS FOR REMOTE-SENSING IN 2 SUB-ALPINE LAKES OF DIFFERENT TROPHIC STATE

Bio-optical measurements were carried out on eutrophic Lake Zug and ol igotrophic Lake Lucerne, to provide data and models for the in situ ca libration of multispectral imagery collected in 1991, during an AVIRIS night over Central Switzerland. The results indicate that Secchi dept h, chlorophyll and total suspended solid concentrations, vertical exti nction coefficient, absorption coefficient and irradiance reflectance in the PAR region can be used to discriminate between the two lakes. D issolved organics concentration, scattering and total attenuation coef ficients estimates, as well as backscattering probability, are less ac ceptable, because of instrumental limitations. Relationships between o ptical and water quality parameters were investigated and found to beh ave according to accepted theoretical frameworks. Both lakes exhibited Vertical and horizontal heterogeneities in chlorophyll and turbidity, and had contrasting mean bio-optical characteristics: although suspen ded solid concentrations were similar, transparency was lower in Lake Zug, but reflectance was substantially higher in Lake Lucerne. Water c olour determined by chromaticity analysis was blue-green in Lake Lucer ne and green in Lake Zug. Reflectance spectra simulated through a thre e-component optochemical model did not completely match those derived from in situ measurements, because of lack of site-specific optical cr oss-sections for suspended minerals and dissolved organics. The monito ring of water quality in subalpine lakes by remote sensing, both with present and future technology, is discussed and considered as possible , provided that their optical behaviour is known, and preferably expre ssed by a valid optochemical model.