TURNING-POINT CONVERGENCE-ZONES IN UNDERWATER SOUND CHANNELS(Ⅱ)A GENERALIZED RAY THEORY

A generalized ray solution,which can be used for calculating the acoustic fields near the causticsand turning points,is obtained by using a generalized phase-integral approximation.This solutionhas a clear physical picture and is convenient for the numerical calculation.The caustic structure andthe intensity distribution at the turning-point convergence-zones in underwater sound channels arediscussed in detail,and the simple and widely applicable intensity expressions are given.The theo-retical analysis shows that for high-pass signals and narrow-band signals,the signals received at theturning-point convergence-zones have the same waveform as the emitted signal or its Hilbert transform.     

浅海中单个简正波的分析

在跃变层之下的等温层中进行了爆炸声传播实验,获得了频率0.32—1.0kH2的单个简正波的记录。通过对简正波脉冲传播时间的分析,确定所记录的波形为第一号简正波。根据第一号简正波的传播特性,分析得到了频率0.32—1.0千赫的小掠射角海底反射系数。     

浅海远程声场的空间相关性与时间稳定性

本文介绍浅海远程声场空间相关的一些实验结果。实验研究了不同距离、频率与带宽的空间相关,测量数据具有明显的距离与频率依赖关系。实验结果表明,在55至130公里的传播距离上跃变层之下的低频声场有较强的空间相关性与时间稳定性。     

负跃层浅海声传播的一个新现象──远程传播中的海底散射波

本文分析了负跃层浅海中的一次声传播实验。爆炸声源位于跃层之下，两个接收水听器分别位于跃层上、下。在远距离处跃层上水听器接受到的信号由两部分组成：从声源直接传播到接收点的多途信号（穿透波）和一个随后到达的强度比前者大得多的信号（散射波）。通过理论计算和数值拟合，我们认为后者是跃层下传播的声波激发的海底散射信号，这部分信号不但可应用于远距离传输，而且还可能用来反演三维海底散射的有关参数。     

一种监测浅海内波的声学方法 *

根据多途结构到达时间间隔大小与温跃层水文环境参数之间的关系 ,研究利用多途结构的变化来监测由内波 (或内潮汐 )引起的温跃层起伏的方法。并从实验上验证了这一方法的可行性     

浅海声传播的波束位移射线简正波理论 *

适用于一般分层浅海的波束位移射线简正波 (BDRM)理论 ,该理论的特点是将边界对声场的影响通过等效边界反射系数来表示 ,因而容易推广到具有切变弹性的海底 .对浅海声场的理论计算表明 ,BDRM理论具有计算精度较高、计算速度较快等优点 .利用BDRM理论计算了浅海中脉冲波形传播 ,理论与实验数据符合比较好 .     

A SIMPLIFIED METHOD FOR IDENTIFICATION AND EXTRACTION OF NORMAL MODE

A simplified method for filtering normal mode in shallow water has been developed.During theexperiment a single hydrophone,placed at different depths,was used to receive the explosive signals at acertain distance.In the laboratory the received signals were filtered in 1/1-octave band centred at a higherfrequency(8 kHz)and in 1/3-octave band centred at several lower frequencies(<800 Hz),and the high-frequency signal was used as the trigger to start sampling the signals at lower frequencies.The theoreticalcalculation and the experimental results showed that for these lower frequencies the depth dependence of thesignals received at different depths by the single hydrophone was similar to the results received by using avertical hydrophone array.And the filtering of the first two modes has been realized by adding the signalsreceived at different depths with the weighting coefficients determined according to the modeeigenfunctions or their signs at the corresponding depths.     

负梯度浅海中的简正波声场

本文讨论简谐点源在负梯度浅海中的声场,文中假定海水声速是随深度单调减小的缓变函数,无需给出具体的函数形式。我们导出了简正波的极点方程与振幅函数的近似表达式,这些公式应用于具体问题容易获得数值解。简正波群速与指数衰减系数的计算公式也具有十分简单的形式,并得到较好的几何解释。     

Pekeris声波导情况下海深不确定性对简正波群速度反演海底声速的影响研究

简正波群速度广泛应用于海底参数反演,海深不确定性对反演结果有较大影响.为了减小海深测量误差对反演结果的影响,本文通过理论分析和仿真计算对Pekeris声波导情况下正则简正波群速度随海深和海底声速的变化规律进行研究,结果表明当所选取的频率处于某号简正波的Airy频率附近时,该号简正波的群速度对海深变化不敏感,而比同频率的...     

Analytical solution based on the wavenumber integration method for the acoustic field in a Pekeris waveguide

An exact solution based on the wavenumber integration method is proposed and implemented in a numerical model for the acoustic field in a Pekeris waveguide excited by either a point source in cylindrical geometry or a line source in plane geometry. Besides, an unconditionally stable numerical solution is also presented, which entirely resolves the stability problem in previous methods. Generally the branch line integral contributes to the total field only at short ranges, and hence is usually ignored in traditional normal mode models. However, for the special case where a mode lies near the branch cut, the branch line integral can contribute to the total field significantly at all ranges. The wavenumber integration method is well-suited for such problems. Numerical results are also provided, which show that the present model can serve as a benchmark for sound propagation in a Pekeris waveguide.