Research Of The Low-frequency Signal Detection In Passive Sonar System

With the fast development of science and technology, sonar system is digitized and intelligentized gradually. Signal detection is one of the most important tasks of sonar signal processing, it's very necessary to design digital and highly performance signal processing system.Passive sonar system detects and judges the target which is based on radiate noise of the target. Line spectrum detection is distinguishing line spectrum of the radiate noise from broad band noise, and detects the sonar target accurately.In this paper, we collect signals from the receiver and stored them, then we use the primary principle to process the signals and at last we have recognition of the target signals. The work of this paper can be divided into some parts:In the stage of the signal detection, we make use of the basic principle of vector hydrophone and do some brief research about signal detecting based on vector hydrophone.In the stage of the data acquisition, we design the analog signals pretreatment circuit first, which adopts an amplifier and filter circuit to modulate the faint signal so that it can be converted into digital by analog-to-digital converter. And the automatic mechanism of signal amplifying is offered, user can adjust the amplifying ratio according to requirement. Then, the system adopts the 16-bit, 250KSPS, charge redistribution SAR, analog-to-digital converter to convert the analogy signal after modulation to digital signal with 45 KSPS throughout. More over, adopts the FIFO (First In First Out)-CY7C4285V as data buffer to avoid frequently reading digital signal by system controller, which advances the performance of system and makes system stable.The data storage module is mainly responsible for reading the data from data buffer and writing the data into mobile hard-disk with file layout through USB bus. In this module solution for mass data storage is realized, which is based on embedded USB Host technology. And the solution is applied in data acquisition system, which makes the system has the ability of mass data storage and long time working. The solution adopts high-performance ARM processor-S3C44B0X and controller circuit ISP 1362 with USB Host function. And the solution realizes the operations to USB devices of Mass Storage Class, and realizes the kind s of operations to file and directory based on FAT file system, such as creating files, deleting files, writing files, reading files and so on.The system is already completed and put into actual application. And the application fully proves that all setting index of the DAS is reached, and that its operation is very easy and convenient.