P.I. Gargett, Ann (Old Dominion University) Proposal #: 0220504 Collaborating Inst: Woolsey, Craig (VA Tech.) Proposal #: 0220745
The PIs propose to construct a two-body towing system to create a stable measurement platform for ocean turbulence measurements. This work builds on the potential for an effective turbulence survey tool using acoustic Doppler current measurements in non-standard ways. In particular, horizontally moving a 5-beam VADCP through the ocean can produce vertical-plane "swath-maps" of crucial turbulence quantities such as vertical momentum stresses, turbulent kinetic energy, and its dissipation rate, as well as standard measurements of mean currents and their vertical shear. These measurements require a sufficiently stable platform, as proposed here. Preliminary offshore measurements taken from a prototype towing system suggest that a two-stage design can provide the required stability. This preliminary testing also clarified the design modifications needed for continuous mapping in offshore environments: provision of shipboard controls for (i) the length of cable between primary and secondary tow bodies and (ii) mean attitude of the secondary tow body. Specifically, the PIs propose to design the necessary control systems, build a complete towing system for operation to depths of 200m, and carry out a coastal offshore test cruise to document the motion characteristics of the system and collect preliminary data with a 1.2MHz 5-beam VADCP, deployed in both upward and downward looking modes. During the course of this work with a shallow system, they will also explore options for accomplishing cable length adjustments in a subsequent system to operate over full ocean depths. If successful, this development would have broad impacts on upper ocean observational capabilities in areas other than turbulence research, enabling spatial mapping of such features as biological thin layers and the near-surface bubble clouds that dominate gas transfer between ocean and atmosphere.
