Sound Source Localization via Cockpit Voice Recorder

Abstract

在飛航事故的調查上，飛航資料記錄器（Flight Data Recorder, FDR）與座艙語音紀錄器（Cockpit Voice Recorder, CVR）均為失事調查的有利工具。而座艙語音記錄器除了駕駛員的通話內容外還會把非語音的聲音一併記錄起來，例如螺旋槳噪音與開關撥動聲等，因此座艙語音記錄器的資料也可以提供飛機失事前駕駛操作開關的狀況，以利失事原因的判別。本論文是基於現有標準的座艙語音記錄器資料的前提下，進行開關聲源定位的研究。傳統的定位方式首先是求得聲源發生後，經由不同傳遞長度到達不同麥克風所產生的抵達時間差（Time-Delay of Arrival, TDOA），再由此定位出開關的位置。我們更可利用同型飛機座艙內的開關位置普遍固定的特性，以及三隻艙內麥克風相對位置所差不遠的前提下，直接建立每個開關相對應的抵達時間差表格，這是最簡化的聲搜尋辦法。另外在此也提出另一個利用Trilateration的方法，來求得由抵達時間差所構成的雙曲面之間的交線，再利用此曲線與座艙配置進行聲源的定位。最後比較出這兩種方式的優缺點與成效，以及利用實驗驗證兩種方式的可行性。The Flight Data Recorder (FDR) and the Cockpit Voice Recorder (CVR) both can strongly facilitate the investigation of aviation accident. Besides the pilot communications, the CVR can also record the non-speech acoustic information as the sound of propeller and the voice of control levers and switches. For this reason, the CVR can provide the last operations of pilots in the accident and assist the investigation. The first step to locate sound sources of switches in traditional method is calculating the time-delay of arrival (TDOA) which is caused by different propagation length form the sound source to different microphones, and the second step is locating the position of sound sources with calculated TDOA. Furthermore, we can introduce the character that the allocations of switches are identical in the same type of aircraft, and premise that the relative positions of three cockpit microphones do not alter substantially. Under the premise, the task of sound source localization in the cockpit could be simplified to a simple table lookup issue, while the table consists of the TDOA set and each corresponding switch. Besides, the other method of hyperbolic positioning via trilateration is introduced. Trilateration is applied to obtain the intersection of hyperboloids which are from the estimated TDOA. Combine this hyperbolic curve and the geometry of aircraft cockpit, and the sound source can be identified. At last, the performances and their pros and cons of these two methods are compared and verified with experiments.Table of Contents文摘要 1bstract Itatement of Contributions II謝 IIIable of Contents IVist of Figures VIIist of Table XIIhapter 1 Introduction 1.1 Motivation ...........................................................................................................1.2 Background .........................................................................................................2.3 Problem Description ............................................................................................4.4 Thesis Organization .............................................................................................5hapter 2 Methodologies of Sound Source Localization 7hapter 3 Localization via TDOA 15.1 The Traditional Sound Source Localization ......................................................15.1.1 Hyperbolas and Hyperboloids 16.1.2 Intersection of Hyperboloids 21.2 Sound Source Localization with Table Lookup Method ...................................29hapter 4 The Factors of Localization Error 32.1 Mechanical Factors ............................................................................................33.2 Environmental Factors ......................................................................................36.3 Anthropogenic Factors ......................................................................................37hapter 5 Parameters & Settings 40.1 The variables and dimensions of simulation .....................................................40.1.1 The Dimensions of Boeing 767 Cockpit 41.1.2 Environment 46.1.3 Sampling rate 47.1.4 Movement of boom microphones 50.2 Process of simulation .........................................................................................51hapter 6 The Simulation of Sound Source Localization with CVR Data 54.1 Simulations of Table Lookup Method ...............................................................54.1.1 Result of localization: Switch 55.1.2 Result of localization: Area 60.1.3 Result of localization: Panel 65.2 Simulations of Hyperbolic Positioning .............................................................67.2.1 Special cases 68.2.2 Result of localization: Switch 70.2.3 Result of localization: Area 75.2.4 Result of localization: Panel 80hapter 7 Comparison of Two Algorithms 83.1 Comparison of two algorithms: Switch .............................................................83.2 Comparison of two algorithms: Area ................................................................84.3 Comparison of two algorithms: Panel ...............................................................86.4 Comparison of two algorithms: Mean accuracy ................................................87.5 Influence of different standard deviations .........................................................89hapter 8 Experiment 91.1 Apparatuses .......................................................................................................91.2 Verification of simple cross-correlation function for time-delay estimation ....94.3 Verification of simple cross-correlation function for time-delay estimation ....98hapter 9 Conclusions and Future Work 104.1 Conclusions .....................................................................................................104.2 Future Works ...................................................................................................105eferences 10