| As the consumption of natural resources increases,the exploitation and utilization of marine resources is of great practical significance to the sustainable development of mankind.Acoustic source localization applications in the ocean are widespread,including fishery,military,navigation and seabed geological mapping.Acoustic source localization in range and depth in an ocean waveguide is a classic research topic,and many scholars have done a lot of work using the matched field processing(MFP)and its variations.Compared with the localization of stationary acoustic source,the localization of moving sources is more complex,and more relevant for practical problems.As is well known,MFP relies on accurate modeling of the acoustic field,particularly its phase,and is sensitive to environmental mismatch when the environmental acoustic information is unknown or incomplete.In reality,the phase of the acoustic field is fluctuating with range and time due to ocean inhomogeneities such as eddies,internal waves,turbulence and so on.This causes significant problems for source localization using MFP.This thesis proposes two phase independent source localization methods for robust source localization.For a source at long ranges,the traditional matched field processing method has the problem of inaccurate phases.The thesis proposes the incoherent MBP method,source depth estimation is conducted in the beam domain using a vertical line array(VLA).Source can be in principle localized by matched the complex data beams with the modeled replica beams.The methods proposed in this paper use only the beam intensities(and not the beam phase)at low(<±30°)thus eliminating local noises from high grazing angles.This method assumes some knowledge of the source range,which is known for active data.For passive data,one assumes that the source location in the x and y plane is known based estimation from two horizontal arrays.If the source range is exactly known,one snapshot of data can be used to estimate the source depth.For a moving source,incoherent MBP accumulated over ranges travelled by the moving source is shown to yield reasonably accurate estimation of source depth.This method is analyzed using simulated data and demonstrated with the SWell Ex-96 data.The paper also analyzes the depth estimation performance of the moving acoustic source in different range span.For a source at short ranges(e.g.,1 km)from the VLA,the received acoustic field is beamformed using conventional beamforming(CBF)to estimate the beam intensity as a function of vertical arrival angle.One can time reverse the beam intensity,treating it as a directional source,for example,using the Bellhop ray tracing program.Where the(back-propagated)rays intersect,the acoustic energy is highest.It yields the source location in range and depth.The technical problem is that the beams obtained by CBF has a wide beam width,producing a somewhat diffused source ambiguity map.Deconvolved CBF is used to solve this problem by the paper.Back propagation of beam intensities is the same as matched beam intensity processing,or incoherent MBP,in theory and is introduced here as it is conceptually more intuitive.The proposed method is applied to autonomous underwater vehicle(AUV)docking problem.Current methods of docking search the bearing of the docking station vertically.It often fails to find the docking station when the SNR is low since transmission loss is depth dependent.This invention finds a method to find the path with high SNR for the AUV to travel directly to the docking station,greatly improving the success rate of docking.It works for a docking station either floating,or towed behind a ship or moored to the ocean bottom.The method is limited to short ranges as ray tracing becomes smeared after saying 1 km.This method is demonstrated with the simulated SWell Ex-96 data.In summary,incoherent MBP has been proposed for robust source depth estimation.Two applications of this method are demonstrated with simulated data or real data. |
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