Research On Techniques Of Passive Positioning In Multi Sea Channels Environment

Passive sonar is the most important detecting equipment in modern underwater acoustical countermeasure. Earlier passive sonar could only estimate the azimuth of a target, but not to range for any targets. It was a major breakthrough that a new kind of sonar being developed, which could estimate the azimuths as well as distances of targets, in the 70s of the last contrary. Being a representative of the newest design architecture, frank passive sonar, which was presented in the 90s, had possessed the furthest ranging capability compared with the rest of onboard passive sonars. However, all of the passive sonars are constrained to range broadband targets only, remaining useless in ranging for impulse targets up till now. Therefore, passive locating for signal impulses becomes a research hot point recently, expecting to have a new breakthrough in the field it belongs.Surveillance signal impulses, which are brought out randomly, are narrow band signals with short durations and unknown parameters so that conventional correlation techniques are not applicable in passive locating for signal impulses, which has to be relied on the traditional amplitude gated time delay estimation called "Direct method" in this dissertation. Precision of direct time delay estimation relies on signal waveforms. Since waveforms of signal impulses will be distorted unavoidably while propagating in multi sea channels, direct estimation fails to meet the precision requirement for passive locating. The technique of channel equalization was applied to improve the precision and stability of time delay difference estimation in this dissertation from the point of view of principles of three points locating based on the analysis of the relativity between time delay difference and time delay estimation errors. Exploiting the inherent relationship between time delay and phase shift together with adaptive processing techniques, multi period compensation method for time delay difference estimation error was developed leading to the reduction of estimation errors. On the basis of aforementioned techniques, the cooperative multi amplitude gated passive locating technique, which is considered as the creative research achievement of this dissertation, was proposed. Applying this technique to process sea trial data, the average relative ranging error at different azimuths is less than 15%, using the test data obtained by radar as references.It is easy to happen, that one or more of the targets while being tracked by conventional frank passive sonar will be lost under the condition that some of the targets were of lower SNR or moving cross over. It is well known that interferences are created randomly while broadband signals radiated by targets are kept stable during the tracking process. The line components of broadband signals radiated by targets will be different if the targets are different from each other. The information of both line component and signal energy of a target was utilized comprehensively by this dissertation to improve the tracking ability. Display mode of type A of an existing system was transformed into pseudo 3D display (type B) by adding historical information of targets accumulated during operation to the screen, resulting in higher detecting probability for lower SNR targets. Therefore, performance of the existing system is enhanced, which is regarded as a contributive research achievement of this dissertation.The technique of sound distribution map of near field noises is of great potential importance in underwater acoustical countermeasure. Because of the interferences of multi sea channels, its performance of near field locating for noise targets will be degraded. By applying virtual array technique to suppress the interferences of multi sea channels, and developing the technique of product sound map, which was proposed by this dissertation, to improve the resolution, satisfactory results were obtained. Besides, direction guided focused beam forming technique had been developed as well, which could not only locate near field target with high precision but also reduce the computation burden by a big margin.Experimental measurements were carried out in this dissertation to verify theoretical predictions.