Use of reflectance band ratios to estimate suspended and dissolved matter concentrations in estuarine waters

In the Tamar estuary (south-west UK), the concentrations of coloured dissolved organic and suspended ( total, organic and inorganic) matter were measured and related to in situ hyperspectral remote-sensing reflectance (R-rs) measurements. A simple method was used to determine the R-rs signal from underwater optical measurements, in order to avoid any surface reflection effects. As previously observed in other estuaries, a large correlation was obtained between the R-rs(850 nm)/R-rs(550 nm) ratio and total suspended matter concentration. The same R-rs ratio was also highly correlated to the inorganic suspended matter concentration. The corresponding relationships are linear. The R-rs(400 nm)/R-rs(600 nm) ratio correlates with the coloured dissolved organic matter concentration, according to a power law regression. These relationships, which appeared to be invariant during the summer period (June-September) and valid for the whole estuary, may be applied to airborne remote sensing data to map the tidal movements of turbidity in the estuary.