An Underwater Target Positioning Technology Based On The Random Floating Type Array

With the rapid development of submarine noise reduction technology in recent years,the noise level of submarines is reducing by 0.5dB to 1dB each year,and their detectable distances are therefore decreasing by 0.5km to 2km annually.Currently,towed sonar arrays and dipping sonars are commonly used to detect and locate underwater objects.The array,towrope and the launch and recovery system of these sonars occupies large space on the carrying vehicle.Meanwhile,the towed body brings negative effects on the maneuverability of the carrying vehicle,which further limits the searching range of the sonar system.These defects pose challenges to the above sonar devices that use beam-forming technology based on regular array.In this thesis we propose a random floating array based underwater object locating technology.The technology deploys many floating nodes on a vast area of water.By acquiring relative location of each random array node,the technology captures the phase difference of the signal sensed by each node.Then energy is focused based on a reference array element and the underwater object can be located.The main research work and innovations are as follows:1.This thesis first proposes the overall design of the random floating array based locating system,then describes the principles of the system in detail.Based on the detailed description,a test prototype of the floating node is designed.The prototype is very scalable.It has a simple structure and is easy to deploy.2.By investigating current research at both home and abroad on sensor node clustering techniques and node self-locating techniques,we propose a real-time array node locating technique by combing homogeneous node self-adaptive clustering technology and underwater chaotic spread spectrum communication technology to resolve the problem of real-time locating error caused by the vast area of monitored water,the large number of nodes andlong-distance communication outage.The technique first clusters homogeneous underwater nodes based on FCM.All nodes are self-adaptively clustered into clusters of similar sizes.The whole monitored water area is therefore partitioned into smaller areas with similar sizes.By using chaotic spread spectrum communication technology,the distance from nodes in each cluster to the cluster center is calculated by TDOA method and nodes in each cluster are located.Clusters communicate via cluster centers to locate nodes in real time.3.A spatial-wave number anti-multipath method is proposed in this thesis to respond to the limited effectiveness of traditional time-frequency filtering method.Our method reduces multi-path effect which exists widely in underwater acoustic communication,creates reliable and stable communication by effectively extracting useful signal in complex background noise.Furthermore,an adaptive spatial-wave number filtering method is proposed to further reduce underwater acoustic communication error rate.4.Finally,we validate the beam-forming technology of random array by simulation.Results show that by knowing locations of each random node and preprocessing signal received by each node using spatial-wave number filtering algorithm,objects can be located by calculating phase differences of all nodes with reference node and superposing signals of other array nodes to the reference node.