Waveguide Invariant Extraction Technique In Shallow Water

There is a stable interference structure in the shallow sound field and the interference structure contains a wealth of targets and marine environmental information.In recent years,it has been widely used in acoustic research,such as the study on marine environment monitoring,passive ranging,and acoustic parameters inversion.A scalar is used to describe interference fringes in waveguide invariant theory.And this theory attract extensive attention and many scholars start to study it since it was proposed.The acoustic propagation model is employed as physical basis to explain and predict various underwater acoustic phenomena.In this paper,the applicable conditions of various acoustic propagation models are analyzed and a new sound model is established based on KrakenC belonging to simple wave theory.Then the formation mechanism of the acoustic field interference structure is studied in detail.The change of the waveguide environment,the depth of the sound source and the receiving depth all can lead to the change of the interference structure of the sound field.Moreover,the waveguide invariants are related to the modal order and the waveguide invariant differs greatly from its approximation under some specific velocity distributions.Therefore,it is still necessary to estimate the waveguide invariants accurately by extraction method,which can provide theoretical basis for its application.In this paper,two kinds of image processing methods,Hough transform and Radon transform,applying to the extractive process of waveguide invariant extraction,are studied.The simulation results show that the processing techniques of two image can effectively detect the straight lines in the image space.Beamforming technology is an important signal processing method applied in the paper and its pool test result is good which mean that beamforming can effectively estimate the target azimuth.Three extractive methods of waveguide invariant are discussed and the applicable conditions of each method are analyzed in detail in this paper.Two-dimensional Fourier transform method is simple and the complex differential equations are avoided.However,the guidance source with known distance information is needed in the application process,which limits the application of the algorithm.Hough transform method can estimate the waveguideinvariant and heading angle when the waveguide invariant is extracted and it is the ideal method to estimate the performance of each azimuth target.However,it demands high stability to the target azimuth which means rapid change of it.Accurate marine environment information and the prediction of the depth of sound source and reception are not necessary when stripe-based beamforming method is employed to extract waveguide invariants.This method can directly deals with the array received signal,but there are some restrictions on the target orientation.Accurate extraction of waveguide invariants can improve the accuracy of ranging,direction finding and etc..This paper analyze the distance measurement and it hopes that the study can make basis for further study on the waveguide invariants.