Investigation into the feasibility of detecting salt fingers optically

Submitted in partial fulfillment of the requirements for the degree of Ocean Engineer at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August, 1972During the last decade there has been increasing interest in discovering the existance of salt fingering in the ocean. The purpose of this investigation was to determine the feasibility of optically detecting salt fingers. Theoretical calculations were conducted on the angular deviation and displacement of parallel light rays propagating through an ordered salt finger model. It is assumed that salt fingers are square cells (one centimeter) with a checkerboard pattern of cells having high and low indices of refraction. The amplitude of index of refraction, above and below the overall average, was assumed to be between 5 X 10-4 to 5 X 10-6. From the computer work it was concluded that an optical method that detects displacement or intensity would have more promise of finding salt fingers in the ocean than an optical method that detects angular deviations. From the computer results and experimental shadowgraph investigations conducted by others, it was concluded that a shadowgraph method is the most promising optical approach to use for detection of salt fingers. Depending on the strength of the salt fingers, the optimum distance between the fingers and the shadowgraph screen may be as far as one to three hundred meters to obtain a sharp image. To shorten this optical path a telescope-microscope lens system cal led a "shadowgraph shortener" was used. Salt finger detection experiments were conducted in a large tank of saltwater. An expanded laser beam (5 centimeters) was passed through the salt water and the "shadowgraph shortener" to fall on a ground glass screen which was photographed with a 16 mm movie camera. The weakest salt fingers detected had a salinity gradient of .02 parts per thousand per 6 centimeters. A survey was conducted on the salinity gradients in the Atlantic Ocean using Nansen bottle data from hydrographic stations. The larger salinity gradients found in parts per thousand per 50 meters were only one order of magnitude weaker than the experimental results. An optical salt finger detector was designed using the same basic set-up as used in the experiments.Prepared for the Office of Naval Research under Contract N00014-66-C0241; NR 083-004

Integrated seawater sampler and data acquisition system prototype : final report

This report documents the work performed by the Woods Hole Oceanographic Institution (WHOI) and the Battelle Memorial Institute from August 1988 to December 1992 in the NSF sponsored development of an Integrated Seawater Sampler and Data Acquisition Prototype. After a 6-month initial design study, a prototype underwater profiing unit was designed and constructed, containing the water acquisition subsystem, CTD and altimeter, control circuitry and batteries. A standard WHOI CTD was adapted for use in the underwater unit and was interfaced to the underwater controller which had a telemetry module connecting ít with a deck control unit. This enabled CTD data to be logged in normal fashion on shipboard while additional commands and diagnostics were sent over the telemetry link to command the underwater unit's water sampling process and receive diagnostic information on system performance. The water sampling subsystem consisted of 36 trays, each containing a plastic sample bag, the pump and control circuitry. The sample bags, initially sealed in a chemically clean environment, were opened by pumping the water out of the tray, thus forcing water into the bag by ambient pressure. The command system could select any bag, and control the water sampling procss from the surface with diagnostic information on system altitude, depth, orientation and cable tension displayed in real time for operator information. At sea tests confirmed the operation of the electrical and control system. Problems were encountered with the bags and seals which were partially solved by further post cruise efforts. However, the bag closing mechanism requires further development, and numerous small system improvements identified during the cruises need to be implemented to produce an operational water sampler. Finally, initial design tor a water sampler handling and storage unit and water extraction system were developed but not implemented. The detailed discussion of the prototype water sampler design, testing and evaluation, and new bag testing result are presented.Funding was provided by the National Science Foundation through Grant No. OCE8821977