Research On Methods Of Suppressing Interference Base On Towed Line Array

Towed line array sonar is one of the most important sonar equipment for ships and submarines.The size of towed line array can be large and the frequency can be low,which makes it easy to find targets of long distance.In practical application,the element position may deviate from nominal position because of the movement of the tow ship and other factors.Due to finite length of the towing cable,there is multipath propagation in shallow sea.Strong far-field interference may emerge in the observation sector.The above problems influence the performance of the towed line array.In this paper,methods of calibration,methods of suppressing tow ship noise and methods of suppressing random interference are researched to improve the performance of towed line array sonar in complex environment.First of all,calibration methods are researched to compensate the distortion of element position.2-D error model of the array shape is established,and then the degradation of detecting performance caused by error of array's position is analyzed.Both non-acoustic methods and acoustical methods are studied to estimate correct position of elements.Theoretical analysis and simulation results prove that these three methods are accurate and suitable for estimating element position.Furthermore,methods of suppressing tow ship noise are studied.According to power spectrum characteristics of marine environmental noise and spatial characteristics of tow ship obtained from sea trial data,the theoretical simulation model is established.null steering beamforming,inverse beamforming and non-data based beam-space transformation are applied to suppress interference of tow ship in this paper.Simulation results and sea trial results prove that,all three methods do better in suppressing tow ship noise and detecting targets than CBF and the performance of non-data based beam-space transformation is the best.Finally,methods of suppressing random interference in the observation sector are studied.Beamforming with minimum sidelobe,matrix prefiltering,beamforming based on subspace reconstruction are studied.It is shown that sidelobe of beamforming with minimum sidelobe is lower than CBF so that it can improve the detectability of weak targets.Matrix prefiltering can get expected filter response so that it can suppress interference in uninterested sector and improve the detectability of interested targets.SIR of beamforming based on subspace reconstruction is improved by reconstructing subspace of interference and signal.The validity of the methods is verified by simulations and sea trial data.