SEDIMENT CONCENTRATION PROFILING IN HEBBLE USING A 1-MHZ ACOUSTIC BACKSCATTER SYSTEM

As part of the High Energy Benthic Boundary Layer Experiment (HEBBLE), a 1-MHz Acoustic BackScatter System (ABSS) was deployed in 4800 m of water on the Nova Scotian continental rise. The purpose of the instrument was to measure non-intrusively a time series of the vertical concentration profile over the course of one year, from September 1985 to September 1986. In this paper, we discuss the details of the ABSS instrument, the results of the time series data analysis, and the implications of the results on sediment transport modeling in HEBBLE. The systematic variation in the ABSS and light transmissometry calibration with changes of particle size distribution caused by environmental variability is discussed. A comparison of the ABSS estimates of particle concentration with those obtained from light transmissometers seems to indicate that the suspended particle size distribution changed surprisingly little throughout the experiment.