The effect of sediment type on the relationship between reflectance and suspended sediment concentration

The use of remotely-sensed optical data to estimate the suspended sediment concentration (SSC) of water is dependent upon the correlation between SSC and reflectance. The strength of this relationship was hypothesized to vary with sediment type, as it is known that sediments, when dry, differ in their particle size distributions, colour and therefore reflectance properties. To test this, the reflectance of pure water with four concentrations of white clay and red silt were measured in the laboratory using a spectroradiometer. The correlation between SSC and reflectance varied with wavelength and sediment type. For white clay the correlations were very high (r≃0·98) in visible and near-infrared wavelengths but for the red silt it was lower (r≃0·8) in blue wavelengths increasing to much higher levels (r≃0·98) in blue/green and longer wavelengths. It was concluded that sediment type can affect the strength of the correlation between SSC and reflectance and that this will be most noticeable at shorter wavelengths.