The Analysis Of Transient Signal Via Underwater Targets

With the rapid development of torpedo technology,how to effectively prevent the torpedo attack and fight as an important research topic on submarines and AW (acoustic warfare).The feature of torpedo related transient signal is the most useful information for torpedo warning sonar.The torpedo related signals, includes some transient signals attributed to the torpedo missile entry into the water,cover sound and ignition of the engine etc.These transient signals compared with other underwater targets signals has unique characteristics which have great significance for long range torpedo warning sonar to find the threats early in time.Firstly,in this dissertation,the process of mechanism analysis,transient signals simulation and experiment research for aerial and submarine-launched torpedo are researched.Aerial torpedo related physical processes are studied,corresponding to various stages of signal characteristics,and impulsive splashing noise,silent period and the pulse of shock period signals are simulated.Transient signals on submarine and torpedo have been studied.On the base of torpedo launch mechanism of the process analysis,transient information is extracted of the corresponding plate covering sound,engine igniting sound and navigation sound.Through the results of simulation and three submarine-launched torpedo experiment data samples,with the especially concerning about covering signal and ignition signal,the characteristics of the sound of submarine-launched torpedo related signals are studied.Secondly,transient signal analysis methods,related with aerial and submarine-launched torpedo,are researched and compared,with the support of mechanism researching.The characteristics of conventional signal processing methods are analyzed.To the examplify the weakness of general TFA method,the time-frequency uncertainty principle and the effect of complex envelope form are simulated on computer.Furtherly,the theory of EMD decomposition is elaborated to study the EMD decomposition performance under different SNR.The results demonstrate that the EMD approach is a robust method suitable for all kinds of SNR application occasions.The 1(1/2)spectrum is the most widely used methods of HOS,and it has a unique harmonic detection,analysis of harmonic components in the presence of a very good treatment effect.Particularly,a multiple components transient signal detector based on the statistics value,is presented in this dissertation.Through simulation and experiment data analysis,it shows that the detector improves the detection ability of the torpedo at lower SNR. For the transient signals of entry into the water,cover sound and ignition of the engine on the process of aerial and submarine-launched torpedo,their corresponding transient signal processing methods are given.For the cover sound , the repeated response and harmonic components appeared in the observation of the results of the transient signal processing,therefore cover sound is suitable for time-frequency characteristics,EMD decomposition,or combination of the two methods;the start peak of entry water signals,whose energy is more concentrated,is the very narrow peak.So the energy detector is conductive to stability detecting,and the follow-up pulsations can be analyzed in EMD decomposition to modal information;The ignition sound signals are complex signals,including the engine noise and propeller noise,so it needs more complex processing method.According to the series of transient signals during the launching of torpedo,this dissertation derives a kind of combined transient signal detector based on the statistical value.Theory analysis and experimental data testify the improvement of detection ratio at lower SNR for the torpedo launching signal's detection.Finally,the location of very narrow pulse onboard is achieved via the 3 elements array,using the short time energy detector.A kind of synthesis method of plate covering signal and torpedo startup signal is designed,and analyzed.It shows the ability to localize the start position of torpedo launching.Through the comparison,the advantage of enlarge the sample length and improvement of precision of localization are discussed.The enhancing,purifying and clustering of line spectrum are researched to foundation the tracking of underwater high speed motion targets.A special after-processed system of 2-order adaptive tracking filter,adapted to the application of passive positioning and tracking sonar,is designed.And the enhancing of weak target trajectory is achieved via Hough transform.All these methods add up to improve the ability to the defense of torpedo for submarine.The research of this dissertation addresses to the problem of analysis of transient signal related with the torpedo startup.Corresponded signal processing methods are discussed.Result of this dissertation will apply to the application of warning,detection,positioning and tracking torpedo for the submarine in the near future.