Post Processing Technology Of Underwater Acoustic Accurate Position

In order to locate and track an underwater moving target accurately, it is required to post process the real-time working-out trajectory. Spacial and temporal post processing methods are introduced respectively in this paper. Spacial post processing is used to improve position accuracy by filtering real-time tracking output. Temporal methods accurate the trajectory by post processing the real-time time delay output. Two kinds of methods are mainly used in temporal post processing, including expert system for selecting the pulses of direct path in case of multi-path environment and correcting the errors caused by the bending rays.On spacial data processing, Kalman filter can be used validly for post processing in underwater acoustic positioning systems. Kalman filter is defined as a recursive filtering method. It is an optimal estimator under the linear and unprejudiced least mean square error rule. It can be applied in multi input-output and non-steady random process. Kalman filter is the least mean square error estimator in Gaussian noisy processes, which is an optimal estimator in all. Kalman filter can improve the target's location metrical precision in effect.The preciseness of time-delay is the key for good location performance in underwater acoustic positioning system. Research on time delay estimation has made successful improvement. Cross-correlation time delay estimator can achieve precision below 1 ms, which is accurate enough (not considering the impact of Doppler). It is more important to consider time delay errors caused by the multi-path effect and the bending of the sound rays than the errors caused by estimators (which is decided by the bend width).Underwater acoustic positioning system locates by measuring the time-delays or time-delay differences of distance pulses from the target to the receiving buoys. The influence on the interfacial reflections is essential to select the direct pulses correctly for proper operation. We select direct pulses by both hardware method and software method to improve position accuracy. After selecting direct pulses, in an underwater channel, sound rays usually propagate along a bending curve because of ununiform of the sound velocity, which would cause great range error in positioning system. So the correction of sound velocity must be considered carefully for a better position accuracy. By studying the ray theory and underwater acoustic channel, mean velocity of sound,recursion method and table-look-up method are used to correct the bending of sound rays for a better positioning accuracy.Finally, simulation and experiment results are given.