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An investigation on underwater acoustic phase measurement in simulated environment

An underwater acoustic phase measurement system and its instrumentation to a precision of 0.5 degree and experimentation in seawater environment are reported in this work. A phase measuring technique using Phase Locked Loop was used in underwater acoustic phase measurements. An underwater sea parameter changes associated with difference in density, temperature, salinity, pressure was studied in laboratory measurement setup with identified necessary tank dimensions along with a standard reference. Phase change of 0 to 360 degrees between radiated and received acoustic signals of 50 kHz, 500 kHz, 2 MHz frequencies over a range of 25 to 30 cm aqueous channel were expressed as a function of sea parameters. The phase difference was studied as a function of salinity for 0 to 30 PSU, conductivity of 0 to 50 mS/cm and temperature of 0 to 50 °C. Comparisons between direct and indirect strategies of measurement were experimented. Calibration carried out with standard reference meters with an accuracy of one parts in 105 was performed.