a bio-optical model for the calculation of suspended matter concentration from moDis data in the Pakri Bay, the Gulf of Finland

A semi empirical bio-optical model was developed for the Pakri Bay. Model input parameters i.e. particle-specific spectral absorption and scattering coefficients and slope factor of coloured dissolved organic matter were calculated from the field data. The modelled reflectance spectra correspond to typical reflectance spectra with low chlorophyll-a concentration. The model is intended for the calculation of suspended matter (SM) concentration maps in the Pakri Bay using the MODIS band 1 reflectance values as input to the model. The linear relationship between the measured reflectance at the MODIS band 1 and the model reflectance was established (R = 0.76, p < 0.01, n = 48), which was used for the correction of the MODIS reflectance values. The spatial distributions of SM concentration in the Pakri Bay were calculated in four ways: (1) using bio-optical model with the MODIS reflectance values with correction; (2) using linear regression between the MODIS reflectance and SM concentration; (3) using bio-optical model with the MODIS reflectance values without correction; (4) using bio-optical model with the MODIS reflectance values with correction, but increasing chlorophyll-a concentration by two orders of magnitude as compared with that in cases 2 and 3. The first two cases produced similar results for SM concentrations, while the latter two gave much higher SM concentrations, especially in the sediment plume. It was concluded that the MODIS band 1 (620–670 nm) is the most suitable for the detection of SM concentrations between 0 and 28 mg l–1.