A flow meter and data logger for ocean microstructure measurement

Abstract

This thesis will cover the development and testing of instrumentation for measuring and recording physical parameters of the ocean. In particular, a three-axis acoustic current meter of superior sensitivity and resolution of low flow velocities is described in the first section of the thesis. In the second section, a digital data multiplexer and magnetic tape recording system is described. This sequentially scans ten sets of data, including the current meters, in addition to temperature, conductivity, pressure and attitude. The data is entered in either frequency or digital words which are stored temporarily in a semiconductor memory and transferred in blocks on to magnetic tape cassettes. A tape reader is also described, which interfaces with a PDP-11/20 computer using appropriate software. The results may then be printed directly, using the computer's teleprinter as output. The complete instrument is built in the form of a framework with a number of underwater housings containing batteries, recording equipment, current meters and other sensors. It is designed to be slightly negatively buoyant, so as to fall freely through the water down a stainless steel wire at a velocity of about 5-10 cm/s, recording measurements from each sensor once per second. On reaching the bottom of the wire (a maximum depth of 500 metres) the instrument is retrieved by reeling in the wire. It is hoped that phenomena such as horizontal layering of the ocean at depths of 100-200 metres will be observable with the instrument, thus leading to a better understanding of the mechanisms, frequency and location of occurrence of such events.