The Research Of DOA Estimation For Targets In Complex Shallow Sea Environment

Due to the influence of seawater's temperature,submarine environment and many scatterers in seawater,the actual ocean channel can't realize the ideal signal transmission without distortion,and it is a complex and changeable uneven channel.Especially in shallow sea channels with more complex environment,the existence of Doppler frequency shift and multipath effect has brought great challenges to the estimation of underwater signals.How to realize more efficient target DOA estimation based on the propagation characteristics of shallow sea channel itself has become a hotspot research in the field of underwater detection.In this paper,the target DOA estimation algorithm in complex shallow sea environment is studied,and the main contents are summarized as follows:1.This paper studies the influence of Doppler frequency shift on DOA estimation of target in complex shallow sea environment,and proposes a joint DOA-Doppler estimation algorithm for shallow sea targets based on compressive sensing.In this paper,a joint DOA-Doppler estimation model of shallow sea target is established,and then through the sparse reconstruction of the wave signal in the DOA-Doppler observation domain,the wave direction of the target and the Doppler frequency shift are estimated,and the array flow vector which effected by Doppler frequency shift is modified.The performance of DOA estimation in shallow sea environment is improved as well.Meanwhile,aiming at the increase of the computation amount of the target in the sparse reconstruction of planar domain,an improved sparse model scheme is proposed,and the observation area is divided according to the iterative idea from the large mesh to the small mesh,which greatly reduces the required running time while ensuring the parameter estimation performance,and improves the efficiency of DOA estimation of shallow sea target.2.This paper studies the influence of multipath effect on the DOA estimation of the target in complex shallow sea environment,and proposes an algorithm for the DOA estimation of shallow sea target based on time reversal-compressive sensing.Firstly,based on ray theory,a shallow sea multipath DOA estimation model is established to quantify the influence of multipath effect on shallow sea DOA estimation.And to solve the interference of shallow sea multipath to channel sparsity when DOA estimation is performed by compressive sensing,the algorithm introduces the time reversal theory to preprocess the signal,and establishes the DOA estimation model of shallow sea target based on time reversal theory.The algorithm uses the space-time focusing property of time reversal theory to correct the multipath distortion.Finally,the validity of the algorithm is verified in different complexity environment with multipath number as the measure of environmental complexity.Under the condition of low signal-to-noise ratio and small snapshot,the introduction of time reversal theory obviously inhibits the side lobe clutter,improves the sparsity of the channel and the signal-to-noise ratio of the array receiver,improves the DOA estimation performance in the complex shallow sea environment,and the performance improvement is more obvious in the environment with more severe multipath effects.