The aim of this study was to estimate the distributions of spectral diffuse attenuation coefficient, attenuation depth and subsurface reflectance of Finnish lakes. In addition, the optimum empirical water quality interpretation algorithms employing reflectance ratios were investigated for the needs of remote sensing. Estimations of the optical properties were based on simple optical models and measured concentrations of optically active substances (the sum of chlorophyll a and phaeophytin a, total suspended solids and coloured dissolved organic matter (CDOM)) at 1670 monitoring stations representing 1113 lakes. The models were parameterized using optical data from 10 lakes. The mean diffuse attenuation coefficient in PAR was 3.5 m−1 and the location of the maximum attenuation depth was in the range 564–714 nm. The simulated reflectance spectra showed a shift of the maximum value to longer wavelengths as trophic status changed from oligotrophic to hyper-eutrophic. High CDOM concentrations decrease the estimation accuracy of chlorophyll a from reflectance spectra using empirical algorithms, particularly in oligotrophic lakes. The models described can be used in studying light availability for photosynthesis at different depths, in the simulation of water temperatures, in estimating how different management alternatives affect light attenuation and Secchi depth, and in various remote sensing applications.

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