A FIBER OPTIC SENSOR FOR MONITORING SUSPENDED SEDIMENT

A new instrument that can be used to continuously monitor concentration of suspended particulates in close proximity to the sea bed (z < 3.5 cm) is described. The instrument is composed of a narrow band source light, a photodiode detector, and glass fibers that transmit and receive light. Individual sensors can be sampled rapidly (8 Hz) and respond linearly to increasing concentrations of sediment over the range 0-100 g l-1. An array of sensors can be deployed from z = 0.5 to 3.5 cm above the seabed providing simultaneous time series of suspended sediment concentration at five discrete elevations. Results of a field deployment in the swash zone of a dissipative beach indicate that the performance of the instrument is comparable to that of the standard optical backscatter sensor (OBS). The data show that sediment resuspension in the swash zone is strongly correlated with low frequency cross-shore flows with peak concentrations exceeding 200 g l-1.