| Obtaining ocean acoustic parameters effectively is the basis of understanding underwater acoustic propagation and mastering the characteristics of underwater acoustic channel,which is an indispensable factor in underwater acoustics researches.Distribution of sound speed in temporal and spatial domain is one of the most important ocean environment parameters,and it has a decisive influence on underwater acoustic propagation.Current can influence ray tracing,and then it will influence the ray travel time,current can also produce Doppler Effect.In our country,most of the offshore area is shallow sea,where the influence of ocean acoustic parameters is much more complicated than in the deep sea.Therefore,the study of sound speed and current distribution in shallow sea area has great significance.On this background,the inversion methods of sound speed profile and the current distribution are studied,according to the ocean environmental characteristics of shallow seas.An inversion method of sound speed profile in the local seas is proposed based on the normal mode grazing angle.And an inverse method of distribution of current in the local seas is proposed,according to the three-point two-way sound propagation current structural model.Two methods is verified by sea tests.The research results have been concluded as following:(1)The inversion of sound speed profile in the local seas based on the normal mode grazing angle at the received pointIn this part,an inversion method of sound speed profile in the local seas is proposed based on the normal mode grazing angle,the source radiated long-pulse signals with a certain band,and the receiver is a vector hydrophone.Firstly,the vector field model is completed based on the ray-normal mode theory,and grazing angles on the received point of each number normal mode are used to establish the cost function.Secondly,to calculate the grazing angle of each number of normal mode,normal modes need to be separated.Since warping transformation can only be used for the short-pulse signals,a new method of separating normal modes based on the improved warping transformation is proposed,each number of normal mode of long pulse chirp signal is separated successfully.Grazing angles on the received point of each number normal mode are available by applying complex sound intensity.In addition,the cost function is solved by hybrid optimization algorithm.The hybrid optimization algorithm combining differential evolution algorithm and quantum particle swarm optimization is proposed,which is used to overcome the disadvantages of single algorithm and can effectively improve the accuracy.The performances of inversion are analyzed,including orders of EOFs,the sensitivity of cost function and mismatching of parameters.It shows that the first 3 orders of EOFs are enough to use for inversion of SSP.Inversion accuracy is associated with the variation of the sea depth,but the influence is very small.The range dependence of grazing angle is small.The inversion error resulting from source and receiver depth may not be taken into consideration for the depth sensor.The inversion of sound speed profile is carried out based on the group delays of normal modes and the propagation time of the fastest eigenray.And simulation results of the three methods are compared.To improve the computational efficiency of the inversion,parallel computing programs are developed for these three methods based on OpenMP,gaining good speedup ratio.The inversion method based on the normal mode grazing angle achieved speedup ratio of 11.21 with a 16-cpu computer.(2)The inversion of distribution of current in the local seas based on the multi-point two-way sound propagation delayIn this part,sources and vertical hydrophone arrays are set to measure the two-way sound propagation delay.Then the multi-point reciprocal current structural model is established,the measurement structure of the multi-points can be merged,and the amplitude and direction of the currents of the surrounded sea can also be obtained.Firstly,the three-dimensional sound propagation model of moving medium is proposed by using ray theory.The two-way sound propagation delay is used to calculate current.By considering the influence of current on eigenrays,the current inversion method is improved so that it can deal with the situation the eigenrays are different for the sender and receiver,and then we can get the vertical structure of current in the sound propagation direction.In addition,by the multi-point reciprocal current structural model,the measurement structure of the multi-points can be merged,and the amplitude and direction of the currents of the surrounded sea can also be obtained,without prior information.Simulation results are verified by the experimental results.The performances of inversion are tested,including the sea depth,the location of the source and receiver,etc.It shows that the seafloor depth matching results mostly effected.Through the two-way sound propagation experiment of time delay,the position of the distance can be modified to reduce the mismatching error.The range dependence of grazing angle is small.The inversion error resulting from source and receiver depth may not be taken into consideration for the depth sensor.(3)The sea trialIn the end,the methods of sound speed inversion and current inversion are validated by sea trials.The instruments are designed by the author,including vector hydrophone and buoys.In the sound speed profile inversion experiment,explosive sound signals and long pulse chirp signals are used.Inversion of sound speed profile is carried out based on the experimental data,and a comparative analysis between the real data and the inversion result is made,which validated each other.In the current inversion,the direct signals extracted from the monitor signals were made a copy correction with the received signals,the multipath structure is gained of the received signals,improving the accuracy of delays of travel time.Simulation results are verified well by the experimental results. |
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