Development and Field Testing of a Lift-Assisted Moored Profiler: LAMP
Ocean water properties (such as temperature and salinity) as well as ocean currents vary with depth and time. Traditionally, long-term ocean observations of a year duration or longer have been made using bottom-anchored moorings that supported an array of instruments distributed along the mooring line and held upright by a surface buoy or subsurface floats. Finite resources usually limit the number of depth levels that can be sampled using such moorings. The WHOI Moored Profiler (MP) instrument was developed 20 years ago (in part with National Science Foundation support) to sample water properties over (near) full ocean depth at high-vertical resolution for time periods of a year or longer. What emerged from the initial engineering work was a streamlined vehicle that employed a traction drive wheel system to propel itself vertically along a conventional subsurface mooring cable of arbitrary length. The prototype profiling vehicle was fitted with a suite of sensors to sample the water properties and currents at sub-1-meter vertical resolution and store the data onboard until recovery. The MP technology was subsequently licensed to McLane Research Laboratories, Inc. for commercial production; those operational instruments (McLane Moored Profilers, MMPs) are presently in use by various groups in support of scientific investigations into ocean processes ranging from basin scale variability to eddies to internal waves, including by the Ocean Observatory Initiative program. While able to return unique and valuable observations, the MMP has only modest endurance (something less than 1000 km of total vertical profiling per deployment) and an uneven track record for profiling reliability (i.e., regular ability to fully span its programmed sampling depth range, particularly at times of strong incident ocean flow). Building on the principal investigators extensive past experience, this project will develop a new moored, profiling instrument that will extract hydrodynamic lift from incident ocean currents to assist with vertical profiling and employ a more capable instrument controller to simplify sensor integration and enhance command and control functionality. A prototype Lift-Assisted Moored Profiler (LAMP) instrument will be designed, constructed and field tested during a 6-month ocean trial. The researchers will subsequently analyze the resulting data and report the results in a peer-reviewed article. It is expected that the new instrument design will attract a manufacturer interested in producing the device under license for broad community use. Engineering student summer interns will be recruited to assist in the design, testing and evaluation of the device. In addition, the research program represents the first opportunity for a young engineer to serve as a co-principal investigator. The acquisition expense of an oceanographic instrument is only part of the cost/benefit equation. While the outlay for a piece of reusable equipment may be amortized over the number of successful deployments of that device, from a scientific standpoint, a failed or only partially successful deployment means loss of information that likely can never be reacquired. It is therefore imperative that oceanographic instruments be designed to be as robust and reliable as is practical. The goal of this project is to improve on the present Moored Profiler design to enhance reliability and operability and thus create an instrument better able to support the oceanographic research programs envisioned for the next decade(s). The technical goals of the project are to (1) improve profiling reliability, particularly in stronger flows, (2) increase profiling endurance relative to presently-available technology, and (3) design and implement an advanced electronics system for the instrument. The development program will have two major thrusts: electronic (design and implement a more capable instrument controller to streamline sensor interfacing, improve the operator interface, enhance the flexibility of the data logging, and collect more and better diagnostics of system performance) and mechanical (design and build a streamlined, low-drag vehicle able to orient relative to the three-dimensional incident flow and extract lift from the ocean currents to assist the drive motor with vertical profiling). The controller will consist of a low-power microprocessor mated with a Linux processor; real-time functionality will be governed by the microprocessor while the Linux subsystem will be activated for higher level processing such as data compression. Lift will derive from wings extending laterally from the vehicle body, with the angle of attack to the incident flow set by an adjustable tail fin (aileron). Preliminary calculations for a wing of total area .387 m2 appears capable of producing a lift force of 21 N for a relative flow of 42 cm/s during profiling (4 times the along-wire drag typically experienced by the McLane Moored Profiler in these conditions). Full scale tests will determine if this conceptual design can achieve significantly greater endurance, or if additional battery capacity will be needed. The program timeline is built around a planned, 6-month trial deployment (spring to fall, 2018) of the LAMP southeast of Woods Hole at 38° N, 68° 40' W in 4100 m water depth. This site periodically experiences upper ocean currents well in excess of 1 m/s associated with northward meanders of the Gulf Stream and associated Warm Core Rings. This test will present significant challenges to the LAMP, and hopefully demonstrate its viability for sustained ocean observation in a wide variety of environments.