Study On Sound Propagation In Shallow Water Environment

Coastal acoustic environments are complicated and always changing, the depth ofcoastal water is shallow, the temperature is sensitive to sunlight and wind or otherfactors; rich of shore-based noises; and also heavy traffic area; morning and eveningtides changing the depth of the water cannot be ignored. All those phenomena havemade the study of sound propagation under coastal environments enduring. Nonlinearinternal waves are always discovered in coastal environments, the great progress hasbeen made in the past30years with many scientists’ efforts around the world. Thefocus of work in this field is how to obtain the parameters exactly and fast. Anyimprovement in this area will help people understand and monitor the oceans simplyand quickly. In this paper some research results using some new thinking and methodsare illustrated which are based on the new experimental data.The normal mode theory and ray theory are popularly used in the study of coastalsound propagation. The study on the relation of these two theories is also hot inacoustics. Characteristics of underwater sound propagation can be effectivelydescribed using waveguide invariants, which are generally described by normal modetheory. By considering that sound propagate in range-independent environments andenvironments consisting of a range-independent background on which a weakrange-dependent perturbation is superimposed.By using the relation between the cycle period of normal modes interferencestructure in the horizontal direction and ray cycle distance, it is certified that, raystability parameter is certified simply to be equal to normal modes waveguideinvariants compared with Brown’s derivation. Theoretical study and numericalsimulations confirm that the structure of ray stability is strongly influenced by thebackground sound speed profile. Ray stability parameter, a new parameter in raytheory, can be used to describe the variation of marine environment and also theunderwater sound propagation. The equivalency between interference pattern ofnormal modes and ray path is verified by numerical simulations, and also the relationbetween ray stability parameter and ray travel time is investigated in environmentsconsisting of a range-independent background sound-speed profile on which arange-dependent perturbation is superimposed. And also the curve of ray stabilityparameter in shallow water is given in the paper, it is clear that, the parameter is alsomeaningful under that condition.In the data processing section, this paper analyzes the Chaoliandao experimentaldata of2013, meanly temperature data and sound propagation data. The statistical properties of temperature data and sound propagation data is researched. It is provedthat, the temperature field model is reasonable. Based on this model and measureddata, the temperature field is reconstructed, and the sound propagation in wholeexperimental time is restored. The results show that, the existence of internal wavesobserved in the offshore experiment changes part of normal mode coefficients(normalized) around0.1. Ray stability parameter values between0and3, or it can goto5or bigger while the internal waves existing. The changing of ray stabilityparameters which depended on the normal modes critical angles, agrees well with thenormal modes coefficients. Consequences and discoveries are summarised in thepaper. Ray stability parameter can be used to describe the variation of marineenvironment and the underwater sound propagation effectively compared with thetravel time, even also can be applied in the acoustic inversion of marine environmentparameters.