Estimating suspended sediment concentrations from ocean colour measurements in moderately turbid waters; the impact of variable particle scattering properties

This study investigates the use of single-band reflectance at visible wavelengths for the derivation of suspended sediment concentrations in the Irish Sea. A reasonably strong relationship was observed between irradiance reflectance at 665 nm (R665) and mineral suspended sediment (MSS) concentrations. Variability in the Reflectance-MSS relationship was found to be the consequence of changes in the mass-specific scattering coefficient (bMSS*) brought about by differences in particle properties such as grain size and composition. A systematic increase in the slope of the Reflectance-MSS relationship was observed with increasing bMSS*. A reflectance model is presented that highlights the dependence of reflectance on bMSS* and suggests that the errors in predicted MSS concentrations can be reduced from 56% to as little as 12% with prior knowledge of the scattering properties of the sediments under study. This paper highlights the need for a complete understanding of the scattering properties of particles in order to accurately estimate MSS concentrations from reflectance measurements. It is suggested that in order to obtain quantitative estimates of MSS in moderately turbid waters from space, it may be necessary to pre-determine scattering efficiencies, bMSS*, for the area of interest.