Modeling And Simulation Of Multibeam Echo Signal In Shallow Sea And TOA Research

Multibeam sounder technology has been widely used in researching seafloor survey due to the advantages of full coverage, high efficiency, high accuracy and resolution.Multibeam echo sounder system gets a late start in China; the main technique for sea bottom detection is based on amplitude detection. At present, there is no feasible scheme in theoretical analysis and realization on using phase-difference detection, and hybrid method which integrates amplitude detection and phase detection is still in theoretical researching.In the first part of this thesis, by analyzing the amplitude of sound signal which is affected by path loss, sea bottom reverberation and uneven water masses, researching the variation of sonic velocity affected by sound speed profile while the signal transmit in the shallow sea, We build up a high frequency(200 kHz )signal model. In building this model we use W.F.Baker model,Lambert model,Mintzer model to simulate the loss of amplitude, and use the constant-gradient sound ray arithmetic to simulate the change of phase.In the second part, we introduce three echo signal processing methods—TVG (Time Variation of Gain),beam forming and demodulation. The application of TVG is mainly discussed.Finally, this thesis introduces two types of methods for estimating TOA(time of arrival ), one is amplitude detection which including amplitude threshold method,amplitude maximum method,special parameter analysis method and WMT, the other is the phase-difference detection. For improving the performance of phase-difference detection, this paper applies a hybrid method which integrates dynamic window and data dynamic averaging. WMT method and our hybrid method are applied to detect simulation signal and real signal. According to the experimental result, we conclude that WMT method has good performance in center-beam, and our hybrid method is benefit to the edge-beam.