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

Abstract

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.

Acknowledgements

This work was supported by a European Marie Curie fellowship (Framework 5, EVK3‐CT‐2002‐50012) and NERC small grant (NER/B/S/2002/00555, PI Lavender). The authors are grateful to the skipper of the Catfish boat and express particular thanks to Dr S. Bass (University of Plymouth, grant NER/M/S/2002/00108) for the use of the pontoon in Calstock and for providing complementary data.