擾動海洋之聲速分佈與距離有關時對聲波脈沖傳播之影響

Abstract

當一聲波脈沖在隨機擾動且有層狀結構海洋中傳遞時，組成脈沖之各個 頻率，將會受到不同程度的亂流散射以及不同的多重路徑傳遞，使得脈沖 產生相當之變形。在本論文中，吾人使用所謂的分割步進數值分析法來模 擬一聲速分佈與距離有關且隨機擾動的海洋環境對載頻為3kHz之聲波脈沖 的影響。由計算結果發現以下之現象：（1）對一單頻波而言，其振幅的 正規化變異隨海洋亂流之擾動強度增加或相關特徵長度減少而增大；（2 ）海洋為一頻率選擇性通道；（3）接收到之聲波波形與接收點深度、聲 速分佈、海洋亂流之擾動強度及相關特徵長度有關；（4）由於回聲及每 次實現模擬中脈沖的遊走，使得脈沖寬度之均方根值為起始值的數倍； （5）脈沖寬度之均方根值隨著海洋亂流之擾動強度增加或相關特徵長度 減少而增加；（6）當聲速分佈與距離有關或與距離無關時，其脈沖寬度 之統計特性相似。 When an acoustic pulse in a random fluctuating ocean with a deterministic sound-speed profile, it is distorted since the every frequency component experience different extents of scattering from the random inhomogeneity and echo numbers. Here, the split-step method is used to simulate an acoustic pulse with a 3kHz carrier propagating through a turbulent ocean with range- independent / -dependent sound-speed profiles. It is found that (1) For a single frequency acoustic beam, the normalized varianc of amplitude fluctuation is increased when the fluctuation strength increases or the scale length decreases; (2) The ocean is a frequency-selective fading channel; (3) The received pulse profile is dependent on the received depth, sound speed distribution, fluctuation strengthand scale length of turbulence in oceans; (4) The rms pulsewidth is broadenedby several times its initial values as a consequence of pulse echoes and pulse wandering of every pulse realization of the ensemble; (5) The rms pulsewidth is increased when the fluctuation strength increases or the scale length decreases; and (6) The statistical properties of the propagating pulse are similar for both the range-independent and -dependent cases in the mean square sense.