Low False Alarm Probability Underwater Acoustic Remote Trigger System

Underwater acoustic remote trigger system, especially remote controlledexplosive systems, require very high security,require very low false alarmprobability and high probability of detection. underwater acoustic remotetrigger system using modern sonar technology, the transmitter launch a set ofcoded,acoustic signal reachs the receiver after a certain distance transmissionin the water medium, and reliable trigs an action. The device is sended to apredetermined locations by the underwater vehicle, then vehicle drive away fromthe launch location, to reach a safe distance place,the operatorder sents orderto launch sound trigger signal to detonate explosives. The system consists ofa transmitter and a receiver of sound fusing mechanisms launcher containsemission transducer, power supply, transmit signal generator, amplifier,receiver contains a receiver hydrophone, power, signal processors. The systemrequirements safety trigging device action when distance is greater than1Km,its receiver false alarms reach to a10-10and detection probability is not lessthan90percent.In the fist we must understand the essence of reaching low probability falsealarm in theory, the DT formula corresponds to the different detection methods,its essence is corresponding to the probability density function of the detectedobject. With the rapid development of digital signal processing, we detectsignal mostly in spectrum domain. different detection methods corresponds todifferent detection threshold.In this article we analyzes the relationshipbetween the probability of false alarm and detection threshold in the spectrumdomain, and verified the correctness of the the results by simulation.Adopt to the engineering requirements, according to the requirements of thedistance and the ambient noise, by using the sonar equation, design systemreasonably and efficiently. according to the probability of false alarm anddetection probability, selected detection index, due to very low probabilityof false alarm,it is difficult to reach the target by alone frequencysingle-pulse， Therefore, we consider quad-band coding form。It can meet the requirements. Because the detected signal is known signal, in order to maximizethe receiver processing gain, the proposed matched filter or signals a longsliding FFT window to match the signal. In order to reduce the minimum detectablesignal to noise ratio, we appropriately increase the signal length. Consideringthe multi-path effects,received singal changs at different depths, differentdistances, different times and downs, we retain sufficient margin to set thesource level. System performance indicators can meet the demand throughtexpected and assessmented.Finally, a prototype lake experiment, the interference signals istransmited near the trigger device receives to assessment its anti-interferenceperformance,it show that false alarm meet the requirements. On the prescribeddistance transmitter and receiver are tested, the system can reliably detect thetrigger signal, the detection probability can meet the requirements. Byanalyzing and evaluating experiment date,it show that the underwater acousticremote trigger system can triggered action security in long distance.