Research On Direction Finding Algorithm And The Real-time Implementation Of Underwater Target

The more deeply people understand the strategic significance of ocean playing in boththe civilian and military filed the more energy people put into the ocean development. Thefirst step to have a knowledge of ocean is to confirm the presence of objects and determinetheir position. So the underwater detection and location technique has been one of the keytechnologies in underwater acoustic field. The main research of this thesis is real-timeomnidirectional monitoring of the underwater target. The main content of this paper are asfollows:The triangular hydrophone array used in the direction finding system is first introducedin this paper. The three equally spaced linear arrays each of which is responsible for the angleranging from-60degree to60degree measurement constitute the triangular hydrophone array.For direction finding one of the three equally spaced linear arrays is chosen as a reference.And the angles got by the three equally spaced linear arrays are changed to angles rangingfrom-180degree to180degree. Then according to the angle got by compass the anglesmeasured by the three equally spaced linear arrays are compensated to angles in geodeticcoordinates. The basic Principle of equal spaced linear array is briefly introduced whilevarious error factors effecting the measurement are calculated and analyzed such as formulaapproximation error, random error, array element installation error and array swinging error.Then the basic measurement method of the time delay estimation is introduced andcross-correlation method to measure the time delay is used in this paper. In order to improvethe accuracy of time delay estimation beam forming achieved by time delay is used to obtainsome certain directivity gain. Different directivity gains got by lap according to a certainattenuation decibels and add of the output after beam forming are compared and the effect ondirection measurement is also compared. Kalman filter is adapted to the direction result to geta smoother target motion trajectory.Finally the real-time implementation of passive direction finding system in theOMAPL-138platform is introduced. The programming of each part algorithm are optimizedso that it can meet the real-time requirement. The real-time measurements of target azimuthangle value and correlation curves are uploaded to the host computer through network and thehost computer displays real-time moving target azimuth process diagram.The passive direction finding module designed in this paper has been tested in both thelaboratory simulation test and the actual lake test verification. Simulation and experimental results show that the module has good real time measurement performance of moving target.