Study On Robust Azimuth Estimation Using Small Scale Sonar Array

With the increasing application of unmanned platform in underwater acoustic detection,small scale sonar has gradually become a research hotspot.The small-scale-sonar array not only has the advantages of small size and convenient installation,but also can realize the azimuth estimation of low frequency targets.At the same time,due to the small array size,the low frequency azimuth estimation performance is not as good as that of traditional large aperture sonar,and it is more sensitive to array error and motion,so the robustness of azimuth estimation is affected.This thesis studies the robust azimuth estimation based on a four-element cross array on a small platform.On the one hand,the factors affecting the robustness of the array azimuth estimation are studied and analyzed.On the other hand,a correction method is proposed for the phase difference error between the array channels in order to improve the accuracy and reliability of the array azimuth estimation.Firstly,the azimuth estimation and performance of the small-scale-sonar array are studied based on the four-element cross array.Based on the four-element cross array,the received signal model and isotropic noise model are constructed and analyzed.On this basis,two azimuth estimation methods based on the cross-power spectrum and MUSIC method are given for the four-element cross array.The influence factors of two kinds of azimuth estimation methods are analyzed,especially the influence of phase difference error between channels on azimuth estimation,and the performance of azimuth estimation of four-element cross array under different environments is given.Then,to solve the problem of azimuth deviation caused by phase inconsistency between array channels,an external field calibration method for phase error between four element cross array channels is proposed.Firstly,using the GPS information of the array and the auxiliary source,a direct correction method for the phase difference deviation between the channels of the four-element cross array is presented,and its performance is simulated and analyzed.Then,considering the array compass deviation,a mathematical model based on multiple azimuth auxiliary sources is proposed to correct the array compass error and the phase difference deviation between channels simultaneously.The array error is corrected based on the direct search method and Newton iteration method respectively,then its performance is analyzed by simulation.Finally,the phase difference between channels is corrected based on the four-element cross array.Firstly,the phase difference characteristics between two hydrophones channels were tested in the air,and the phase difference characteristics between channels and the effect of multi-path interference on phase correction were analyzed.Then the phase correction of the array is carried out in the pool,and the influence of the near-field environment of the pool and the multi-path interference on the phase correction is simulated and analyzed.The calibration test is carried out in the pool and the test data is processed.Finally,the phase calibration of the array is carried out in the Marine environment,and the calibration method is verified by the experimental data.