MEASUREMENTS OF CONCENTRATION, PARTICLE SIZE AND FLUX OF SUSPENDED PARTICULATE MATTER WITH ACOUSTIC DOPPLER VELOCIMETER AND OPTICAL BACKSCATTER SENSOR

Simultaneous measurements of velocity and concentration of suspended particulate matter (SPM) have been carried out using an acoustic Doppler velocimeter (ADV). Since the acousticbackscatter is a strong function of particle size, the size information is drawn from measure ments supplemented by an optical backscatter sensor (OBS). In the settling experiment, the SPM concentrations estimated from a combination of ADV and OBS show good agreement with the gravimetric particulate concentrations. Field measurements have been performed in the bottom boundary layer of the Ota river estuary. The SPM concentrations measured by a combination of ADV and OBS are in good agreement with those from seawater samples. The mean size from the ADV/OBS response ratio is 5.5-7 μm. The concentrations and turbulent fluxes of SPM increase with the shear stress. The concentration profiles are also obtained from ADCP echo intensity.