An analysis of the acoustic characteristics of ABSS (acoustic backscatter system) and its deployments

The benthic boundary layer is the interface between the world ocean and the earth beneath. Extending from the top of the Ekman layer, where bottom drag begins to exert its influence on the general oceanic circulation, down to a few centimeters below the sediment surface, it is the site of exchange of momentum, heat, solutes and suspended load. To aid in investigating these zones the ABSS (Acoustic Backscatter System) a combination 5 MHz - 1 MHz system is deployed by the High Energy Benthic Boundary Layer Experiment (HEBBLE) team on the Nova Scotian Rise at a depth of 4800m. This device can, without entering the observed flow, sense suspended sediment simultaneously in over 100 1-cm range bins, as frequently as one hundred times per second, while the low frequency transducer of ABSS looks upward through the Ekman layer, using the same measurement principle, but in 20 cm range bins. Inasfar as their sampling density in space and time for turbulent fluid mechanical data, these devices are quite unprecedented.