Waveguide Invariant In Shallow Water: Theory And Application

Waveguide invariant research is one of hot topics in underwater acoustics. Thisthesis mainly studies the exploratory research around waveguide invariant in shallowwater, including both basic and practical researchs. The former examines therelationship between waveguide invariant β and environmental parameters, andextending the dedispersion transform to summer conditions. The later examinesArtificial Time Reverse based on DeDispersion Transform(DDT-ATR), and acousticmonitoring of the thermocline height by acoustic intensity interference-pattern. Themain contributions are as follows:(1) Following the definition of waveguide invariant, the thesis try to find therelationship between waveguide invariant β and environmental parameters. Thefocal point of the work is about the influence of thermocline parameter on thewaveguide invariant β. A theory relation between thermocline and waveguideinvariant β is provided. A good agreement between the theory and numericalsimulation in high frequency band has been found.(2) After exploring the adaptability of Dedispersion Transform, the thesis extend theapplication scope of dedispersion transform to typical summer condition. Thismethod is verified by the numerical simulation and sea experiement data.(3) A method of artificial time reverse based on dedispersion transform (DDT-ATR)has been proposed in this thesis. By applying DDT anddelay-and-polarized-summation on VLA data in a successive order, the finaloutput of DDT-ATR compressed in time and focus on source depth. The methodis verified by Yellow Sea real data.(4) According with waveguide invariant β≈1in high frequency, the thesis proposea method to monitor temporal variation of thermocline position by acoustic intensity interference-pattern. To validate the idea, both simulation and AEYFI-05（Acoustics Experiment of Yellow sea Oceanic Front and Internal Waves2005）experiment data processing are performed. An excellent agreement betweeninversed thermocline position and that monitored by the thermistor chain suggestsa potential of long-term acoustic monitoring of the thermocline position insummer conditions.