理想负跃层浅海中脉冲波形的理论分析

Theoretical analysis on pulsed waveforms in shallow water with an ideal thermocline

随着信号处理技术的发展，对信道传输特性的研究与利用日益受到重视。多途传输是水声信道的基本特征。在典型的负跃层浅海实验中早已观测到脉冲信号具有规则的多途结构，用射线理论可以定性地解释所观测到的脉冲多途结构，但射线理论不能精确地获得脉冲的相位与幅度信息。本文利用具有波束位移的射线－简正波（ＲＭＢ）理论，计算了理想负跃层情况下带限信号的波形。为了检验本文方法的计算精度，我们用ＭＯＡＴＬ简正波算法计算了同一问题。比较表明，两种方法的计算结果是一致的，但本文方法的计算速度至少高两个数量级。研究表明，在跃变层情况下波束位移对于波形结构的计算起着关键作用。本文的结果进一步证明了具有波束位移的简正波衰减公式的正确性。利用本文方法研究了收发深度、距离、信号频率及海底参数对脉冲波形的影响。

In this paper, waveforms of band-limited signals have been calculated under the condition of an ideal thermocline by the ray-mode with beam displacement (RMB) approach. A comparison between the RMB appoach and MOATL code shows that the RMB apprach is a fast and accurate method and the run time by the RMB appoach is reduced by about two orders of magnitude. Results reveal that beam displacement makes a great difference to waveform calculation under the condition of thermocline, and validity on mode attenuation formula with beam displacement is further proved.The pulsed waveforms depending on source and receiver depths, transmission range, signal frequence and bottom parameters have been discussed.