The Study Of Detection Of Underwater Object Based On Multistatic Sonar System

Because of the separable resource and receiver, multistatic sonar has many special characters in underwater target detection and localization. At present, the research of multistatic sonar has been paid much attention by people. In this thesis, the studies about positioning methods in applying the multistatic sonar are carried out according to the features of this kind of sonars. By simulation, The performances of several methods are compared and evaluated. The main contents of this thesis are summarized as follows:1. The sonar equations of bistatic sonar are developed from an energy point of view. The meaning of the parameter and the effects in sonar equations are studied. Based on analyzing the location principles and errors of multistatic sonar, the localization errors with Geometrical Dilution of Precision(GDOP) are also described in this thesis.2. Aiming at the problem of underwater object location in bistatic sonar, six basic location methods and an optimized method of two-dimensional target are discussed. The performances of four algorithms are evaluated via computer simulations. The geometrical distribution of errors is given. Moreover, the accuracy analysis for different measurements and parameters(such as time measure error, azimuth measure error, buoys error, baseline length and sound velocity fluctuation) are given respectively. To make the best use of the observation datas, the weighted least square localization algorithm is used to improve the accuracy in bistatic sonar. The simulation results show that the positioning accuracy of this algorithm is higher than the other four algorithms, with which the positioning accuracy in stations areas and side areas can be improved effectively. 3. Four algorithms used in positioning three-dimension target are discussed when three measurements can be obtained. The positioning accuracy contours are drawn to evaluate the location performance via computer simulation. The accuracy analysis for different measurements and parameters are given respectively. The simulation results show that the positioning accuracy is influenced by azimuth error greatly. In practice, it can get much better positioning performance to improve azimuth accuracy. Comparing the positioning accuracy in the situation of two-dimension with that in three-dimension, the latter is lower. The reason is that the error of the height is introduced.4. Extending the positioning method in bistatic sonar to the study of multistatic sonar, the algorithm using distance data is discussed. Besides, the geometrical distribution of error in different station layout and the best precept of station position are analyzed.5. The mechanism that produces the three types of reverberation and the correlative characteristics of reverberation are discussed in the thesis. Some methods to restrain reverberation are developed. Three scattering models(bottom scattering, surface scattering and volume scattering model) in bistatic sonars are developed and simulated. The simulation results show that there are many factors to influence the reverberation, each of them has different contribution to the reverberation, and the angles configurations and the characters of interface have main function, and the effect of the change of sound velocity on reverberation can be ignored.The conclusions drawn from the research can provide the reference to further research and devise the bistatic sonar.