Research On Techniques Of Bottom Parameters Acquirement In Shallow Water

The geoacoustic properties of the ocean bottom have a significant effect on acoustic propagation in shallow water. Sonar performance prediction and matched-field localization systems that make use of geoacoustic information are limited by the lack of high-resolution geophysical databases to describe the frequency- and range-dependent acoustic properties of the sea bottom, especially in shallow water environments. However its properties are probably the most difficult things to be measured directly because of costs, this is the reason why inversion of acoustic pressure field data for the estimation of seabed geoacoustic parameters has been a topic of considerable recent attention in underwater acoustics. Comprehensive theoretical researches and field experiments have been conducted to obtain geoacoustic data for bottom mapping, sediment classification and estimation of other environmental parameters (sound speed and current fields...). There are several different methods to solve the inverse problem, including matched-field processing using nonlinear global optimization methods, linearized perturbation techniques, and tomographic imaging methods.This dissertation is written based on the ray theory of acoustics, which had been developed earliest and has the simplest physical figure. The inversion structure of the sea bottom is assumed to be parallel layered bottom, we use this model to generate the receive signal and processed with matched filtering for geoacoustical parameter estimation. The inversion is formulated as an optimum problem. Since Genetic Algorithms (GA) can be used for global search with self-consistent probability, it can overcome the difficulties while solving nonlinear problems using linear methods, so it had been used to solve the nonlinear least square problem of inversion model. The global optimization or the second best solution will been obtained. It had been proved theoretically by simulation results that the inversion method is effective for determination of acoustic parameters of the sea bottom.Finally, the data in DaLian field experiment are processed by inversion method developed before. The results of the inversion consist with the results of profile experiment and the characteristic values of other literatures before. That is to say that the method for geoacoustical parameters estimation can be used in practical.