使用拖曳式水下麥克風陣列之飛航紀錄器水下偵蒐及定位

Abstract

本研究目的為建立一套拖曳式水下麥克風陣列系統，作為海上空難發生時之可攜式海空難搜救水下聽音定位設備。水下定位發報器(Underwater Locator Beacon, ULB)是裝設於飛航紀錄器(Flight Recordor)上之設備，若海上空難不幸發生時，在落入水中後便會短路並以固定周期發出單頻脈衝訊號供搜救人員進行搜索，進而打撈飛機殘骸並了解肇事主因。本研究以建置之拖曳式水下麥克風陣列系統於台東外海進行實驗，佈放一低頻率8.8kHz水下定位發報器做為聲源，並以拖曳式水下麥克風陣列接收訊號後進行聲源方位計算，驗證此系統於水下定位發報器聲源定位之可行性，同時於實驗時量測該水下定位發報器聲源位準。定位部分本研究利用麥克風陣列上多個麥克風之特性，並假設聲波在遠場及平面波傳遞之情況下，藉由匹配濾波器找出水下定位發報器訊號傳遞到不同麥克風的到達時間，再透過到達時間差(Time Difference of Arrival,TDOA)與入射聲波角度與陣列之間三角幾何關係計算相對於水下麥克風陣列之聲源入射角，進而得出水下定位發報器位置。除了聲源方位角計算外，本研究也以高斯射線群法針對水下定位發報器主要頻率進行音傳損耗模擬，以模擬結果對應實際音傳損耗下知音傳距離，推估聲源距離，輔助定位結果。除了硬體設備建置外，軟體部分以PAMGUARD做為主要架構進行訊號接收及介面顯示，介面內容可即時提供輸入訊號之時頻譜圖、陣列深度、GPS位置及錄製四通道音檔，即時顯示時頻譜圖可於海上搜救時即時觀測有無接收到水下定位發報器之訊號，並透過內建Click Detector模塊可進行即時訊號偵測及定位，能夠提高海上搜救效率。

The goal of this study is to build an underwater towed hydrophone array system as a portable system that can search the flight recorder when an aviation accident occurs on the ocean. The underwater locater beacon (ULB) is an equipment installed on the flight recorder. When the plane crashes into the ocean and the ULB falls into water, the ULB will be triggered and make transient pulse signals in a fixed period to let the rescue personnel search the location of the flight recorder. Finding the flight recorder can help investigate the cause of the accident. In this study, an experiment using the towed hydrophone array system was conducted in Taitung offshore. This experiment used a low frequency ULB (8.8kHz) as a sound source and receive the signal by the towed hydrophone array to verify the system is capable in localization of the ULB’s signal. Also measured the sound pressure level of the ULB in this experiment. To localize the ULB, assumed the sound source is in the far field and transmitted as a plane wave. This study use Matched filter to determine the arrival time of the ULB’s signal and use the Time Difference of Arrival (TDOA) between different hydrophone in the array to calculate the bearing angle between the sound source and the array. Besides caculate the bearing angle this study also use the Gaussian Beam tracing method to calculate the Transmission Loss (TL) of the ULB signal and correspond the actual TL in experiment to estimate the distance of the sound source. Apart from building an underwater towed hydrophone array system, this study also use PAMGUARD an open source software as an interface to show the incoming time series signal, spectrogram, array depth, GPS position and also recording the four channels sound file. The real-time spectrogram can show whether the signal of the ULB is received. Also through the built-in Click Detector module, real-time signal detection and positioning can be performed to improve the efficiency of the searching and rescue operations.