The Method Research Of Passive Target Detection Using DEMON Spectrum And The Project Design Of Processing System

The passive target detection and identification is the important research part in the modern acoustic technology field. The covert characteristic of passive sonar makes the submarines can get the target information without being detected easily by the enemies' detection equipment. The information includes target azimuth, distance, speed, type, etc. The native and foreign researchers have done a great deal of work in this field to improve the ability of sonar systems. The radiated noise of ships always is composed of high-frequency continuous spectrum and low-frequency line spectrum that has great energy. The line spectrum is made by the cavitation noise. It appears that there is much linear spectrum composed of base-frequency and each harmonic. The base-frequency is related with the propeller rotation speed and the number of blades on the propeller, so it is steady in some way. Many people have strong interest in target line-spectrum research for its stabilization in long time.Great deal of work has been done in targets line-spectrum detection and identification. We have had good method to do with the single target, but to multiple targets, we have not perfect detection result, especially when these targets are in the same direction. Their own base-frequencies are difficult to be separated when they are in the same beam. They look very disorderly in the spectrum. It will be very hard to differentiate them only using our eyes with the low SNR, saying nothing of the machine auto-identification. Basing this question, trying to auto-detect and auto-identify the base-frequencies of multi-targets is one of our most important work.There is much information about the targets in the envelope spectrum of the signals received by the passive sonar system. In this paper, we build the mathematic models and the envelope detection model of the ship noise. Through analyzing the envelope spectrum, we separate the line spectrum, from which we then detect the target base-frequency related with the rotate speed of ship screws. At the same time we can get the precise target azimuth, etc. In this paper, we give one or more solutions to every question, and do the contrastive experiments withthe emulational data and real data separately. Finally, we give a kind of hardware system solution, by which we can design and ameliorate the algorithm of target detection and identification, and the display system. All the work has been finished with a good effect.