| When planes and ships crash at sea,it is of great significance to search and rescue the crashed targets at the first time.Aircraft and ships are usually equipped with driving information recorders(commonly known as "black boxes"),and an information beacon is installed in the information recorder for underwater positioning.When the information recorder sinks into the water with the wrecked target,the acoustic beacon automatically starts to work and emits periodic acoustic pulse signals.Therefore,the Underwater Acoustic Localization(UWAL)method can be used to search and rescue the wrecked underwater target.Underwater targets are stationary on the ocean floor.During search and rescue,a single platform is constantly moved for multi-point measurement,and then the information of multiple measurement points is used to determine the target position.However,due to the high-temperature and low-temperature environment of the ocean floor,the signal transmission period of the acoustic beacon will be slightly distorted,and the signal period cannot be accurately known,so it belongs to an unknown period to a certain extent.The UWAL method is mainly divided into a positioning method based on a Direction of Arrival(DOA)information and a positioning method based on a delay information.This paper first studies the positioning method based on DOA information.The DOA information of the target is not affected by the variation of the signal transmission period,so the DOA information can be used to effectively locate the unknown periodic acoustic beacons.According to the spatial position distribution of the target and the positioning solution nodes,the DOA-based positioning scene is divided into plane angle positioning and space angle positioning.For each positioning scenario,a physical model and a mathematical model of positioning are established in this paper.The positioning errors are calculated theoretically,and the distribution characteristics of the positioning errors are analyzed.On the other hand,this thesis studies the positioning method based on delay information.Traditional positioning methods based on delay information mainly include positioning methods based on Time of Arrival(TOA)and time differences of Arrival(TDOA).To locate in the process of motion search,the two methods need time synchronization information or accurate signal period information respectively,so they cannot be applied to the positioning of unknown periodic acoustic beacons.Aiming at this problem,this paper establishes the physical concept and definition of Second Order Time Difference of Arrival(STDOA),and proposes a localization method for unknown periodic acoustic beacons based on STDOA.The theoretical analysis results of positioning accuracy show that the proposed STDOA-based positioning method has high positioning accuracy,which is close to the traditional positioning method based on delay information.On the basis of the above theoretical research,this thesis designs and develops an unknown periodic acoustic beacon positioning software based on the needs of actual engineering projects.The software is based on the Qt Creator platform and adopts a functional modular design,including system initialization,data communication,positioning solution algorithm,file management and other modules,which respectively realize the test parameter setting,data transmission,positioning result calculation,and test information storage functions.Finally,laboratory joint test,pool test and lake test were carried out respectively,which verified the validity of the method proposed in the paper,the correctness of the theoretical analysis and the reliability of the software developed.The experimental results confirm that both the STDOA-based positioning method and the DOA-based positioning method can effectively locate unknown periodic acoustic beacons.Among them,the STDOA-based positioning method has better positioning accuracy,while the DOA-based positioning method has faster convergence and better robustness. |
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