The effects of variability in the inherent optical properties on estimations of chlorophyll a by remote sensing in Swedish freshwaters

During late summer of 1997 measurements were made of the inherent optical properties in Lake M¨alaren, Sweden. These included measurements of the total particulate absorption, phytoplankton absorption, yellow substance absorption and total backscattering. Measurements were also made of concentrations known to affect the inherent optical properties; chlorophyll a and suspended particulate organic and inorganic matter. At the same time measurements of underwater radiance reflectance were made. The above measurements were used to better define the relationships between the inherent optical properties and the concentrations affecting them. Correlation analyses were also made in order to study covariation of the concentrations of suspended and dissolved substances in the data set. These relationships were then used to better parameterize a semi-analytical model predicting remote sensing reflectance. Multivariate sensitivity analyses showed that large variations on the RrŽ700 710. RrŽ678 685. ratio vs. chlorophyll concentrations could be expected in a heterogeneous environment such as Lake M¨alaren. This could lead to large errors in subsequent estimates of chlorophyll concentrations.