Research On Key Techniques Of Near-field Passive Positioning

Focused beamforming is a passive positioning method which is suitable for the short-range noise source.But there are still many problems of its application in the accurate positioning of the moving target in shallow water.The array shape error and the coherent multipath channel will lead to the mismatch of the array manifold.The Doppler will reduce the correlation between the signals receipted by different elements.In this paper,the sub-arrays are used.Aiming at the above problems,several techniques were researched,which are the calibration technique for hydrophone array shape with sources in near field,the broadband passive Doppler compensation and motion estimation technique,the multipath compensation and 3-D positioning technique.They'll lay the foundation of the accurate passive positioning of the high-speed moving target in near field.Considering the requirement of the near-field calibration under multipath condition,two methods are proposed which are suitable for the installation error of the sub-arrays.Firstly,integrating the near-field spherical wave model and the Taylor approximation theory,the 2-D error model of the array shape is established,and the linear relation between the error and the eigenvector is achieved.Then a new accurate near-field pilot-calibration method of the array shape is proposed based on it.Secondly,according to the unconditional maximum likelihood theory,the objective function of nonlinear optimization problem is constructed.Another novel near-field calibration method for array shape is put forward based on maximum likelihood estimation,which can be used as the both pilot-calibration and self-calibration.The impact of multipath on the calibration is studied.Assuming that the reflections are the coherent sources with known position,the matched strategy is presented using the property of eigen decomposition.Theoretical analysis and simulation results prove that,these two calibration methods are accurate and suitable for the strong reflections.Finally,the lake trial verifies the validity of the proposed methods.High-speed will lead to a big difference between Doppler coefficients of the receipt signals with the target in near field.And it reduces their correlation.Aiming at the problem,two Doppler compensation methods are proposed based on the frequency domain correlation and the feature extraction.They can not only compensate the Doppler for the broadband signal precisely,but also reduce the calculation comparing with the ambiguity function.In order to further improve the capability of the integrated array,the relation is derived between the Doppler coefficient and the parameters of motion.The differential evolution method is used to fuse the data.Based on the Doppler,the real-time passive estimation method of the state of motion is achieved.The performance of the above algorithms is analyzed by numerical simulation.It validates that the Doppler compensation method can modify the Doppler impact of the focused beamforming.The validity of the state of motion passive estimation is proved.Multipath makes the spatial spectrum of the focused beamforming appear the false highlights,which impact the positioning.Two techniques are researched to suppress the impact,which are multipath model match and virtual time reversal mirror.In order to realize the 3-D positioning using a horizontal linear array,a cepstrum estimator of the time delay of reflections and a 3-D positioning method are put forward.The cepstrum expression of the underwater acoustic channel is derived.Utilizing the geometric relationship between the time delay and the target location,and the redundant information of all the sensors,the problem of solving equations is changed into a nonlinear optimization problem.Then the 3-D positioning method is achieved through the signal synchronizing and the calculation with Levenberg-Marquardt(LM).The simulation and pool test validate that,the above methods are effective and applied.