Researches On Key Technologies Of Active Detection Of Offshore Underwater Small Target In A Large Bistatic-angle Configuration

Currently,the detection of underwater small targets mainly relies on active sonar,which actively emits detection acoustic signals and collects echoes generated by objects during the propagation process to determine the target.Detection of large bistatic-angle configuration is a mode of active detection,which is mainly used to detect moving targets passing through or near the transceiver line.The target strength under large bistatic-angle configuration is large,and even if the target covers the anechoic tile,the target strength will not be reduced.Currently,there are two main aspects of research and analysis on the problem of detection of large bistatic-angle configuration: firstly,the model and characteristics of underwater small targets under detection of large bistatic-angle configuration conditions;The other is the research on the detection and extraction methods of large bistatic-angle scattering signals.This article mainly studies the acoustic scattering characteristics of underwater small targets and the suppression methods of direct blast interference in large bistatic-angles.The main work of the thesis is as follows:The acoustic scattering characteristics of underwater small targets were analyzed.The scattering sound fields of spherical targets with regular geometric shapes and underwater autonomous vehicles with complex shapes were calculated separately,and rigorous theoretical solutions and finite element results were obtained.The scattering waveform of underwater small targets was analyzed.Taking the target as a linear time-invariant system,the time domain scattering waveform of the target is obtained when the incident waveform is known.The simulation results show that the backscatter waveform amplitude of the target is larger than that of the large bistatic-angle waveform,and the backscatter echo has elastic surrounding waves,which is more complex than the scattering waves under the large bistatic-angle condition;The viscoelastic anechoic layer has little effect on the waveform of large bistatic-angle.When a certain frequency is reached,the viscoelastic layer can play the role of "anechoic" on backscatter echo.Research on direct blast interference suppression method based on adaptive filtering algorithm.Aiming at the direct blast interference problem in Detection of large bistatic-angle configuration.A direct blast suppression method based on adaptive filters has been proposed.The main content of this method is to first establish a training dataset using the direct blast matrix when there is no target,obtain the weights of the adaptive filter,and use the output error at this time as the default detection output background.When the target approaches and crosses the transmission line,the input filter is a mixed signal of direct blast and scattered wave interference,which cannot match the previously trained weights,resulting in an increase in error output and a change in the detection output curve.When the target crosses the line and moves away from it,the error output will decrease until the original default background is restored.A performance test was conducted on the large bistatic-angle.Completed the monitoring of the summer hydrological environment in a certain water area of Qiandao Lake,and obtained hydrological information such as sound velocity profile,flow velocity profile,and sound propagation loss.We have completed the measurement of the scattering intensity of the scaled target as a function of the target attitude angle and analyzed the reasons for the errors in the results.A detection experiment in large bistatic-angle configuration was conducted to verify the feasibility of the adaptive direct blast suppression algorithm.