Passive Ranging Method Of Underwater Broadband Impulse Source In Shallow Water Waveguide

The multi-path and dispersion characteristics of shallow-water waveguide represent an important research area in the field of underwater acoustic.Broadband sound pulse signals hold abundant target and environmental information through propagation in shallow-water waveguides.Hence,target information and environmental parameters can be extracted by analyzing the propagation and time frequency characteristics of received normal-mode signals.First,the dispersion characteristics of a non-ideal waveguide are studied thoroughly.This waveguide leads to my major task of deducing the dispersion function and modified warping transformation.Second,several passive ranging methods for underwater broadband impulse sources with a single hydrophone are proposed on the basis of normal-mode signals,which are separated and extracted effectively from the received signals.Finally,the validity and accuracy of all methods are analyzed by theoretical simulation and experimental data.The structure of the paper is described in the ensuing sections.1.Normal-mode separation and extraction method.This study is aimed at realizing the separation and extraction of normal-mode signals in a non-ideal waveguide.The dispersion characteristics of the non-ideal waveguide are studied on the basis of beam-displacement ray normal-mode theory.The results lead to the deduction of the dispersion function and modified warping transformation on the basis of the seabed phase shift parameter P.The warping transformation in the non-ideal waveguide can be modified without the sound speed,density,or even absorption coefficient of the seabed.The simulated results of different types of waveguides suggest that the proposed method can improve not only the frequency aggregation under normal mode in the transformation domain but also the separation capability relative to the case of traditional warping transformation.In addition,the simulation results illustrate that the separation performance in the modified operator is slightly affected by the mismatch of environmental parameters.2.Passive ranging of broadband impulse sources in shallow-water waveguides based on characteristics of normal mode signals.For the passive ranging of broadband impulse sources in the shallow-water waveguide in this study,the method based on match mode with a single hydrophone is put forward.The phase difference of two normal modes extracted by a received signal is employed as the measurement field.This field,in turn,cancels the influence of sound sources on the phase of the different-order normal mode.The seabed phase shift parameter P is employed to calculate the replica,and the source range can be estimated by matching the measurement field and replica.The effects of the distance measurements on the different waveguides,sources,accepted positions,and mismatching of environmental parameters are simulated.The results indicate that the source and receiver positions exert a negligible impact on ranging outcomes for a shallow-water waveguide with uniform and negative gradient sound speed profiles.On the contrary,the seabed phase shift parameter P can be used to indicate seabed characteristics in case the receiver is located near the seabed for a thermocline waveguide.The mismatch of the seabed phase shift parameter P exerts no effect on the performance of the ranging method.The passive ranging method based on group delay with a single hydrophone is proposed.Each normal-mode dispersion curve is extracted by time-frequency analysis and warping transformation.Furthermore,the time delay difference between the two normal modes is calculated by retaining the influence of the environment.The group slow-speed difference ?Sg,mn can be calculated by the seabed phase shift parameter P,and the range of the underwater broadband pulse sound source can be estimated according to group delay theory.A simulation is carried out to verify the accuracy of the time delay difference and group slow-speed difference.In addition,the effects on the range are analyzed.These results illustrate that time delay and slow speed difference are identical to the numerical results of KRAKEN.Moreover,the ranging method has relatively good tolerance in relation to the seabed phase shift parameter P.The validity and accuracy of the two methods are also proved by the data processing results of in-situ experiments.3.Research on passive ranging method based on Bayesian theoryAn underwater acoustic parameter inversion method based on normal pressure signals is proposed to solve the problem regarding the passive ranging of broadband pulse sound sources in shallow seas being dependent on environmental parameters such as sea depth and sound speed.The proposed method is derived from Bayesian estimation theory.The normal-mode signals in the frequency domain are used as the measured field in Bayesian theory.These signals are extracted from the received signal by employing a single hydrophone.The replica is calculated by employing KRAKEN.The environmental parameters and sound source positions can be inversed as unknown parameters.According to the posterior probability density distribution of the inversion parameters,the underwater acoustic parameters are estimated and found to exhibit good environmental tolerance.The sensitivity and inversion results of the parameters are analyzed through simulation.The results illustrate that the cost function is sensitive to entire parameters.The inversion results for the source positions are accurate,and the error is infinitesimal.An acoustic parameter inversion method based on dispersion curves is proposed to solve the problem of multiple inversion parameters and slow speed calculations in the above method.The extracted dispersion curve of each normal mode is used as the input signal of Bayesian estimation theory.The replica is calculated at a rapid pace by the seabed phase shift parameter P.In addition,the entire parameters are inversed according to Bayesian estimation theory.The simulation results show that the cost function is sensitive to each parameter and that the calculation speed of the replica is fast.In case of the seabed phase shift parameter P employed to represent the sea bottom characteristics,the number of inversion parameters is relatively few,the inversion efficiency is high,and the inversion results are accurate.