Inter-comparison of turbidity and sediment concentration measurements from an ADP, an OBS-3, and a LISST

A two-year study is being conducted jointly by Stevens Institute of Technology and Rutgers, The State University of New Jersey to create a sediment budget for the Port of New York and New Jersey to further the understanding of the physical processes responsible for persistent siltation of New York Harbor. Scientists are investigating the extent to which marine sediments are suspended due to meteorological events, dredging practices and/or vessel traffic. Thus far hydrodynamic and sediment concentration measurements have been made twice in 2000 and thrice in 2001 in Newark Bay, the Arthur Kill and the Kill van Kull using multi-instrumented moorings deployed simultaneously at the three sites for two to four week periods. Each mooring contains a SonTek Acoustic Doppler Current Profiler (ADP), a SeaBird MicroCat CTD, a D&A Instruments OBS-3 and a Sequoia Scientific LISST-100. The optical measurement obtained by the OBS-3, which can be translated into suspended sediment load, is dependent on grain size distribution and concentration. The acoustic backscatter intensity from the ADP can also be used as an indicator of turbidity in the water column, which is dependent on grain size distribution and concentration, as well as particle shape and density. The LISST, a laser forward-scattering instrument, reports the sediment concentration and the grain size distribution from 1.25 to 500 μm in situ. The measured concentration is dependent on sediment concentration and shape as the LISST assumes that all particles are spheres. A comparison of time-history signals among the LISST, the OBS-3 and the ADP was conducted to examine whether changes in the OBS-3 and ADP output signals represent real changes in sediment concentration, or merely changes in grain size distribution and particle composition