Research On Passive Location Of Water Entry Noise Of Objects

In the field of underwater acoustic technology, acoustic positioning technology is an important part of the research contents and has a significant branch named passive positioning technology. Passive positioning technology can locate the target by its own noise only, thus it is widely used in military and civilian applications because of the good concealment. Aerial torpedo will produce a noise signal in the process of diving into the water, so the research of locating the water entry objects such as aerial torpedo is of great value. The main goal of this paper is to propose a passive location technique of the target by the use of its entry noise.The contents are divided into the following sections:1, the water entry process of an object is introduced, an analysis and simulation about target splashing and gas bubble pulsation produced in this process is made and then the research and simulation of acoustic multi-path channel are also accomplished, finally, the method of energy ratio is used to measure the time delay. The results show that splashing pulse signal is strong enough that can be used as the passive location source signal, and the superimposition of direct sound wave and reflected sound wave has a little effect on the measurement of time delay when using the method of energy ratio under the multi-path influence.2, the advantages and disadvantages of different acoustic positioning system are introduced, short baseline positioning system is chosen to locate the water entry targets, and ternary array positioning system and four-element array positioning system are the main research contents. This paper select different formation in both two positioning systems to study, the formations includes: regular triangle array, right-angled triangle array, arbitrary triangle array and square array, rectangle array and arbitrary quadrilateral array. The results showed that the ternary array solver method can produce two sets of solutions whose distribution is related to the formation and four-element array can solve the location coordinate of targets directly, what's more, the positioning effect of four-element array is slightly better than ternary array under the condition that they have the same delay error.3, the complete program of passive position is written by the use of C language, the program includes the filtering stage, the judge stage, time delay measurement stage and location stage, and the program of location stage is written in the form of subroutine which is convenient for the calls to the actual project.4, the passive location experiments are carried out in the pool, ternary array and four-element array forms are both used to processing the experimental data. The results obtained by the two methods are compared and the reasons why the position error are caused are concluded after the analysis, the strengths and weaknesses about these two methods are also compared. The results show that the vertical resolution of the ternary array is poor and the position error is large, while the quaternary array has an accurate result with smaller error.This paper starts with the signal model construction of the target, which combines the water entry process with the characteristic of the acoustic multi-path channel, and then utilizes the energy ration method, the time delay between different elements can be measured. After the derivation of ternary array or four-element array location equation, a program using language C is developed. The research gives a complete process of the passive location method using short baseline positioning system, which is testified with actual use and proved its feasibility.