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

The water turbidity measured with optical methods (transmittance and backsc attering) is usually expressed as beam attenuation coefficient (BAC) or for mazin turbidity units (FTU). The transformation of these units to volumetri c 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 fi eld calibrations between BAG, FTU and SSC are presented and "best-fit" cali bration curves are shown. These calibrations represent an "average" from di fferent marine environments of the western Mediterranean (from estuary to c ontinental slope). However, the general curves can only be applied fur desc riptive or semi-quantitative purposes. Comparison of turbidity measurements using the same sensor with different calibration ranges shows the advantag e of simultaneously combining two instruments calibrated in different range s when significant changes in suspended sediment concentrations are expecte d.