Studies On Underwater Acoustic Localization Technique In Shallow Water And Its Application

Underwater acoustic localization technique can be widely used in the military affairs and oceanic scientific areas, it plays an important role in warranting our country's safety and making the construction all right. The long base line positioning system based on time measurement has a high positioning resolution and it can act on larger areas than other systems, so it is one of the most commonly used positioning systems. The mathematical positioning models depend on the way the system works and there are many mathematical models such as spherical model, hyperbolic model and so on. Whatever mathematical model it is, the slant range between the target and the hydrophones is obtained by multiplying the time measurement by the acoustic sound velocity. The estimation of the target is obtained by solving a set of nonlinear equations. By far, the acoustic sound velocity is usually considered as a constant value, which is determined by the experience. The constant empirical acoustic sound velocity is well suitable for the case where the acoustic sound velocity changes slightly with the water depth, or the ray reflection can be ignored in the deep water, or the localization area is small. In shallow water, the ray reflection on the surface and the bottom must be considered, thus the acoustic sound velocity changes seriously with different eigenray. Under the above analysis of the acoustic sound velocity, the shallow water acoustic localization technique based on shallow water acoustic sound velocity is studied in this dissertation to improve the precision of the range measurement and the localization.It is well known that the shallow water acoustic localization technique mainly consists of two parts: one is the establishment and computation of the acoustic model and the other one is the positioning algorithm. The establishment of the acoustic model is the basis of the localization problem and the ray tracing theory is commonly used. The ray in shallow water is very complex because of the complexity and multi-path character in shallow water. By far, the acoustic models based on the ray span have such limitation as low computational resolution, not finding all eigen-rays and so on. This dissertation does a lot of research on the ray in the shallow water and uses the finite automaton (FA) to establish the acoustic model. The ray tracing is following the Snell's law. The acoustic model based on the FA can overcome the disadvantage stated before and has a high computational resolution. The numerical simulation verifies the validation and correctness of the proposed acoustic model.The effective sound velocity(ESV) varies with different eigen-rays, a common conclusion is drawn after the numerical simulation and experiment studies, that is the ESV has a higher acoustic positioning resolution than the empirical acoustic sound velocity. Based on the ESV in deep water, the ESV in shallow water is developed and brought through. The ESV in shallow water can be computed by the FA acoustic model. In order to satisfy the requirement of the real time character, the ESV in shallow water table building method and table lookup method are used and the numerical simulation studies verifies the correctness of the proposed methods.As another part of this dissertation, the quasi-3D mathematical positioning model with known water depth, the redundant terms in the hydrophone networks, etc., are studied. The numerical simulation draws many conclusions. The quasi-3D mathematical positioning model is dominated by the known water depth and the 3D mathematical positioning model should be used first whenever possible. The redundant terms which make the nonlinear equations be over-determined cases can get a higher positioning resolution. Some useful conclusions are obtained by analyzing the ambiguity and non-solution of nonlinear algorithm, the geometric dilution of precision (GDOP). The numerical simulation results are consistent with the theory results. These results are of significance in the application of the technique. The shallow water acoustic localization technique is of great importance in the country's safety and construction affairs. Some theoretic and numerical studies have been taken and the results are helpful to discuss the oceanic detection and exploration, the ocean engineering construction, the ocean environment detection and underwater submersible vehicles localization.