Field calibration of optical sensors for measuring suspended sediment concentration in the western Mediterranean

The water turbidity measured with optical methods (transmittance and backscattering) is usually expressed as beam attenuation coefficient (BAC) or formazin turbidity units (FTU). The transformation of these units to volumetric suspended sediment concentration (SSC) units is not straightforward, and accurate calibrations are required in order to obtain valuable information on suspended sediment distributions and fluxes. In this paper, data from field calibrations between BAG, FTU and SSC are presented and best-fit calibration curves are shown. These calibrations represent an average from different marine environments of the western Mediterranean (from estuary to continental slope). However, the general curves can only be applied fur descriptive or semi-quantitative purposes. Comparison of turbidity measurements using the same sensor with different calibration ranges shows the advantage of simultaneously combining two instruments calibrated in different ranges when significant changes in suspended sediment concentrations are expected.