Underwater Ultrasonic Close Range Moving Target Detection Based On Multi-frequency Modulated Signal

In recent decades, underwater acoustic detection systems have made great progress andhave been used in military, commercial, and other circumstances broadly. Underwater movingtarget detection, however, still has limitations. The detection of moving targets is an importantbranch of the of underwater ultrasonic probe field. In this thesis, based on the research Chirpsignal, I put forward the multi-frequency modulated signal to be the transmitted signal ofunderwater moving target detection, combined with fractional Fourier transform and arraysignal processing techniques to study underwater target motion parameter estimation. Themain work and innovation:1. Research and analysis on the underwater environment, including underwater acousticvelocity, background noise, Doppler Effect, multi-path effects. And introduce of the principleand classification of underwater detection systems. According to the Doppler effect and therelationship of the signal frequency, using the obtained chirp class the signal echo the tonefrequency to target movement speed estimation method.2. Then put forward the multi-frequency modulated signal to be the transmitted signal ofunderwater moving target detection, by the effect of Doppler frequency shift to chirp signaland the characteristics of the underwater ultrasonic signal. To improve detection accuracy andreduce the detection error, based on chirp signal based on a multi-frequency modulated signalsuch a composite signal, and use in the following thesis as a target detection of underwaterultrasonic movement.3. Then proposed the use of the FM signal echo fractional Fourier transform to estimateunderwater moving target speed and distance parameters. Through the study found, the bestmulti-frequency modulated signal fractional Fourier transform order tune the frequency of theecho signal is obtained, and the echo time delay estimation based on optimal fractionaldomain focus point coordinates obtained thus the speed of the moving target is obtained withthe distance parameter. 4. Put forward the method of multi-frequency modulated signal array signal processingcombined with informed underwater moving target orientation parameters. By more than agood FM signal focus, the proposed use of the fractional Fourier transform separation andtransformation of multi-frequency modulated signal, divided to be the single-frequencysinusoidal signal with a direction parameter, then use the MUSIC algorithm based onfractional Fourier transform these sinusoidal signal applied to multi-FM signal DOAestimation, get the direction of the underwater moving target parameters, so to achieve themulti-frequency modulated signal DOA estimation.5. Then accomplish the algorithm simulation above. Respectively, to complete thesimulation estimated based on the speed and distance parameters of a single moving targetmultiple FM signals and multiple moving targets, and by the mean square error comparedproved using the FM signal better parameter estimation accuracy and stability than usingLFM signal. Finally, the algorithm is proposed to estimate the improved algorithm andsimulation to achieve target direction of movement based on multi-frequency modulationsignal.