Research On Impulse Response Function Calculation Method Of Range-Dependent Underwater Acoustic Channel

In order to improve the real-time and verisimilitude of real-time element-level signal simulation under range-dependent conditions,aiming at the limitations of the existing normal mode model,parabolic approximation model and ray model in performing element-level real-time simulation,the optimization methods of underwater acoustic channel propagation characteristics and channel impulse response function calculation under range-dependent conditions are studied in this paper.In view of the limitation that the KRAKEN model cannot get the propagation characteristics of range-dependent channels,the MOATL model based on the adiabatic coupled normal mode theory is improved.The normalized calculation formula of the eigenfunctions is used to realize the normalization of the MOATL eigenfunctions.Outputs of the parameters such as eigenvalue and eigenfunction are added,which are required for channel frequency response calculation.On this basis,the calculation of the ocean channel impulse response with horizontally slowly varying environmental parameter is realized,which makes up for the deficiencies that the MOATL model can only calculate the channel propagation loss.In view of the shortcomings of the complicated configuration of environmental files when calculating the multi-frequency point and multi-environment parameter propagation characteristics of the MOATL model,the frequency resolution parameters participate in the MOATL model calculation,and the program script is used to improve the MOATL model calling method.These methods jointly achieve the simplification of MOATL model configuration file and improve the operability of MOATL model.The traditional Fourier synthesis methods for broadband modeling need large amount of calculation when it requires high frequency resolution.To solve this problem,an eigenvalue interpolation method of normal mode based on the theoretical equation of adiabatic coupling normal mode horizontal wave number is proposed,and the interpolation formulas of real part and imaginary part of adiabatic coupled normal wave eigenvalues are derived.At the same time of reducing the number of propagation model code calls,high-resolution Fourier synthesis broadband modeling is realized.The simulation results show that,under the requirement of ensuring simulation accuracy,the amount of calculation can be reduced by90%,and by 95% in the case of 20 Hz resolution.The RAM model can only output the calculation results of the channel frequency response while the parameters such as eigenvalue,eigenfunction and group velocity are absent for frequency response interpolation and impulse response function optimization.To solve this problem,a window estimation algorithm for channel impulse response function is proposed based on group delay energy joint screening criterion,which realizes estimation of the start time and window length of the impulse response function.Simulation results show that compared with the traditional Fourier synthesis algorithm,the impulse response length can be reduced by 90%,and the channel frequency response similarity reaches 0.99.Since the number of eigen ray of the BELLHOP model fluctuates greatly under various ocean environment parameters,source frequency and source receiver relative position,it is difficult for a single screening criterion to insure both the real-time and similarity of the array signal simulation results.To solve this problem,the fitness function of genetic algorithm is designed to give consideration to both energy criterion and time criterion.In addition,the ray-screening criterion based on genetic algorithm is proposed,which realizes the screening of eigen ray of BELLHOP model in various application scenarios.The simulation results show that compared with the traditional ray-screening criterion,the ray screening results not only ensure the energy but also effectively reduce the duration of the channel impulse response.