Research On Positioning Techniques Of The Underwater Moving Target Track Based On Two-dimensional Imaging Sonar

Measurement techniques for underwater moving target all have wide application prospectswhether in the military or in the civilian areas. Generally, there are interior and exterior meansto measure the3D motion trajectory of underwater moving targets. The interior measurementacquires the relative motion status information through velocity and attitude sensors installedinside the moving target and then calculate the motion trajectory via data post-extraction andpost-processing. Moreover, the exterior measurement commonly makes use of USBL, SBL,LBL, underwater optical imaging or underwater acoustic imaging. Except the above twoimaging means, any other means all have to install the appropriate equipment on the movingtarget. However, there is no installation condition for relative equipment in many special cases,thus whether acoustic beacons or interior measurement all can’t be used in such cases. Due toits sensitivity to environment change, the performance of optical imaging is directly influencedby the water turbidity, which may cause coarse measurement errors or even invalidate themeasurements. Fortunately, the above problems can be overcome by making use of the highresolution imaging sonar. Though the3D high resolution imaging sonar is the best choice, itcan’t be implemented because of test site and immature techniques. Besides, the2D imagingsonar can only achieve the2D measurement of underwater moving target. After considering therelative technical needs and implementation conditions, a scheme adopting two2D imagingsonars for measuring the3D motion trajectory of underwater moving target is proposed in thisdissertation. In order to fulfill the special demands of device installation, the whole systemdesign is optimized, which have been validated in the trial effectively.In the first chapter, it introduces the research background and meanings firstly. Then itsummarizes the state of the art, the performance parameters and imaging results of the mainproducts about oversea and domestic side-scanning sonar, forward-looking sonar, acoustic lenssonar and synthetic aperture sonar. Herein, it concludes the key technology of underwater targetmotion measurement system studied in this dissertation. In the end, it gives the specificstructures of the following research work.The second chapter focuses on the real-time imaging technology for the high-speedmoving target under the strong reverberation background. Firstly, it introduces the principlesand performance about the conventional beam-forming (i.e. time-delay sum beam-forming).Because the conventional beam-forming can’t meet the requirements of real-time imaging, theFFT beam-forming is studied for real-time and easy implementation. Aiming at the system requirement working in the near field, it extends the traditional FFT beam-forming based on thecenter beam of multi-points focused at different distances and gives a FFT beam-formingalgorithm on the basis of multi-beams focused at different distances in the condition of broadbeam (the studied measurement system with scanning fan of90degrees), meeting therequirements of the imaging quality of near-field and real-time imaging. Secondly, due to theinfluence of the strong reverberation, the received echoes are not simply Doppler shift butDoppler spread, which causes the FFT beam-forming ineffective. In this dissertation, abroadband beam-forming method is proposed by making use of the characteristics of targetechoes. And this method solves the imaging problem of high-speed moving target in thecondition of strong reverberation.The third chapter presents the method to calculate the3D motion trajectory of underwatermoving target through two2D high resolution imaging sonars. According to the imagingcharacteristics of2D imaging sonar, it proposes a method of calculating3D trajectory via2Dintersection. And then it analyzes the error sources of the measurement system, establishes thesolution model of the measurement system and derives integrated measurement errors ofdifferent error sources. The theoretical and numerical simulation all has validated the proposedalgorithm.In the last chapter, the software and hardware structures of receiving and transmittingsonars are optimized, considering the installation and working requirements of themeasurement system. And the specific scheme is introduced and implemented. The tank trialindicates:(1) the imaging performance of the two2D imaging sonars meets the system index (i.e.range and azimuth resolution);(2) the proposed method to calculate the3D trajectory position based on the two2Dimaging sonars satisfies the demand of measurement precision;(3) the proposed imaging algorithm of high-speed moving target can suppress thereverberation effectively and improve the imaging quality for high-speed moving targets.