Underwater Acoustic Array Signal Processing Technology For Underwater Fast Platform Interference Suppression

The fast small platform is the main combat weapon in modern naval warfare,it is guided to the target direction through wire guidance method.It can be launched from the tube without the prerequisite of accurate target motion parameters,which greatly shortens the reaction time of the weapon system.But when launching from tube,the fast small platform becomes a strong broadband interference to affect the local sonar platforms.According to the interference forms in the stage of launching and moving,this paper proposes different interference suppression beamforming algorithms.When the fast small platform trajectory can be accurately forecast,the interference can be suppressed by setting the zero constraints in the forecast direction.In the early launching period,the rapid small platform stays in the near field while the target is in the far field,for the near field spherical wave propagation characteristics,a revision of the zero constraints beamforming algorithm is done to revise the time delay brought by the spherical wave.And the suppression technology for multiple highlight model interference is derived and simulated.Although the sonar platform away from tube such as towed array can be used to eliminate the influence of near field factors,but if the predicted direction is not accurate enough,the interference suppression performance of zero constraints will decrease rapidly.In this paper,when the linear array element spacing satisfies certain wavelength relation,adjacent array element can be combined to produce heart shaped directivity,adjust the fast small platform launching direction to null direction,the interference from the array endfire direction can be decreased.For broadband array signal,the resampling technique is used to focus the broadband signal on the frequency which meets the directivity requirement,further suppress the broadband interference and detect the target.In the early and middle movement period,the fast small platform has high speed,which leads to the rapid variation of receiving data and target direction,and a few available snapshots.If one sonar array is supposed to finish tasks of both tracking the fast small platform and tracking the target,then a smaller number of snapshots will be used for the adaptive beamforming.Combined with the fast small platform characteristics of rapid movement and small number of available snapshots,some adaptive robust interference suppression techniques including diagonal loading and covariance matrix tapers are studied.A robust broadband adaptive anti rapid target interference beamforming algorithm is proposed,which can make full use of the broadband gain of the source.Finally the feasibility and robustness of the algorithm are verified with simulation and sea trial data.In the late period of fast small platform movement,its azimuth changes slowly,distance is far,then the signal component,interference component and noise component in the receiving signal covariance matrix all change slowly,and there are lots of available snapshots,so covariance matrix estimation is relatively stable.When the probability statistics of noise and target signal are independent,the noise component mainly concentrates in the main diagonal of the receiving signal covariance matrix.According to this characteristic,this paper proposes the underwater acoustic array signal processing algorithm based on diagonal reduction.For underwater environment of high background noise level,the proposed method can effectively improve the multi-target resolution performance with low SNR.Based on theoretical derivation,the diagonal reduction coefficient is calculated,without estimating the source number in advance.For broadband signal,this paper proposes a steered minimum variance beamforming algorithm based on diagonal reduction.Sea trial data verifies that this algorithm is effective and robust,and is better than the incoherent broadband processing method,improving the multi target resolution of spatial spectrum estimation.The results also verify that the diagonal reduction technique is very suitable in low SNR underwater acoustic array signal processing environment,and has great value for engineering application.