Impacts of Environment-Dependent Acoustic Propagation on Passive Acoustic Monitoring of Cetaceans
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IMPACTS OF ENVIRONMENT-DEPENDENT ACOUSTIC PROPAGATION ON PASSIVE ACOUSTIC MONITORING OF CETACEANS by Carolyn M. Binder Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Dalhousie University Halifax, Nova Scotia July 2017 DRDC-RDDC-2017-P060 c Her Majesty the Queen in Right of Canada, Minister of National Defence, 2017 For my family. I couldn’t have done this without your support, dedication, and love. ii TABLE OF CONTENTS List of Tables ..................................... vii List of Figures .................................... ix Abstract ........................................ xiv List of Abbreviations and Symbols Used ...................... xv Acknowledgements ................................. xix Chapter 1 Introduction ............................ 1 1.1 Literature Review .............................. 1 1.2 Investigating the Impacts of Environment- Dependent Propagation on an Automated Aural Classifier ......................... 4 1.2.1 Thesis Outline ........................... 6 Chapter 2 Automated Aural Classifier and Performance Metrics ..... 8 2.1 The Aural Classifier ............................. 9 2.1.1 Validation of Classifier Performance ............... 10 2.2 Performance Metrics ............................ 13 Chapter 3 Biogenic and Synthetic Vocalization Data Set .......... 18 3.1 Biogenic Whale Calls ............................ 18 3.2 Synthetic Whale Calls ............................ 21 3.2.1 Comparison of Synthetic Calls with Biogenic Whale Calls .... 23 3.3 Conditioning and Upsampling of Signals for Experiments ......... 27 3.3.1 Time Series for Transmission ................... 31 3.4 Signal Detection ............................... 31 Chapter 4 Propagation Experiments ..................... 33 4.1 Introduction ................................. 33 4.2 Experimental Set-up ............................ 34 4.2.1 Acoustic Recording Equipment .................. 38 4.3 Ocean Environment Measurements ..................... 39 iv 4.3.1 Wind Speed and Surface Roughness Conditions .......... 39 4.3.2 Ambient Noise ........................... 40 4.3.3 Sediment Properties ........................ 41 4.3.4 Sound Speed Profiles ........................ 42 4.4 Source Level Estimates ........................... 45 4.4.1 Method 1: Transmit Sensitivity and Transducer Input Voltage . 46 4.4.2 Method 2: Received Signal Level on Monitor Hydrophone .... 48 4.4.3 Source Level Results and Discussion ............... 50 4.5 Experimental Results and Discussion .................... 53 4.5.1 Example Decision Regions ..................... 54 4.5.2 Summary of Performance Results ................. 58 4.5.3 Training Set Selection ....................... 64 4.6 Chapter Summary .............................. 69 Chapter 5 Pulse Propagation Modelling ................... 71 5.1 Background ................................. 71 5.1.1 Broadband Modelling with Fourier Synthesis ........... 77 5.1.2 Waveform Transmission Through a Channel (WATTCH) Propaga- tion Model and Bellhop ...................... 79 5.2 Simulation of Experimental Conditions .................. 85 5.2.1 Environment and Model Configuration .............. 85 5.2.2 Noise Addition ........................... 87 5.2.3 Results and Discussion ....................... 91 5.3 Sensitivity to Environmental Parameters .................. 95 5.3.1 Environment and Model Configurations .............. 96 5.3.2 Results and Discussion ....................... 97 5.4 Chapter Summary ..............................101 Chapter 6 Relative Impact of SNR and Other Propagation Effects ....103 6.1 Introduction .................................103 6.2 Separating Contributions of Propagation-Induced Distortion and SNR . 105 6.2.1 Case 1: Adding Noise .......................106 6.2.2 Case 2: Adding Propagation Effects ................107 6.2.3 Case 3: Adding Noise and Propagation Effects ..........107 6.2.4 Results and Discussion .......................107 6.3 Increased Range Resolution ........................111 6.3.1 Methods ..............................111 6.3.2 Results and Discussion .......................114 6.4 Chapter Summary ..............................119 v Chapter 7 Impact of Environment-Dependent Propagation on Automatic Recognition of Bowhead and Humpback Vocalizations .....121 7.1 Environment and Model Configurations ..................122 7.1.1 Noise Addition ...........................125 7.2 Results and Discussion ...........................127 7.2.1 Isospeed Environment .......................127 7.2.2 Downward Refracting Environment ................129 7.3 Chapter Summary ..............................133 Chapter 8 Conclusions ............................135 Appendix A Mooring Diagrams .........................141 Appendix B Determination of Hydrophone Depth on SHARP Mooring ...146 B.1 Background .................................146 B.2 Determining Hydrophone Depth Via Ray Theory .............148 B.2.1 Method ...............................148 B.2.2 Results and Discussion .......................150 B.3 Determining Importance of Recorder Depth to the Aural Classifier Perfor- mance ....................................152 B.3.1 Method ...............................152 B.3.2 Results and Discussion .......................153 B.4 Summary Remarks .............................155 Appendix C Temperature-Salinity Diagrams .................156 Appendix D Arrival Structure ..........................158 D.1 Method ...................................158 D.2 Results and Discussion ...........................162 Appendix E Selection of Sediment Parameters ................164 E.1 Impact of Sediment Density on Propagation Effects and Classifier Perfor- mance ....................................166 E.2 Summary Remarks .............................167 Bibliography .....................................169 vi LIST OF TABLES 3.1 Frequency range and duration of whale vocalizations in the biogenic data set. ................................ 19 3.2 The five features that best discriminated between bowhead and humpback whale calls. ........................ 25 4.1 Depths of hydrophones deployed during both days of the Gulf of Mexico sea trial. ........................... 36 4.2 Transmission ranges of signals during the Gulf of Mexico experi- ment ................................. 38 4.3 Sampling formats for acoustic recording packages. ......... 39 4.4 Transmission loss values used for estimating the source level of transmitted signals. .......................... 51 4.5 Estimated source level of transmitted signals. ............ 52 4.6 Number of detections and classifier performance for biogenic bow- head and humpback calls recorded by the icListen on mooring 4. 54 4.7 Number of detections and classifier performance for synthetic bow- head and humpback calls recorded by the icListen on mooring 4. No uncertainty estimates are provided here for the classifier perfor- mance results because k-fold cross-validation was not implemented. 57 5.1 Summary of the main considerations when selecting a numerical technique for ocean acoustic pulse propagation modelling. ..... 76 5.2 Ranges over which signals were propagated through the WATTCH model for each of the receiver depths. ................ 87 5.3 Example performance values for signals propagated through the WATTCH model over 6.5 km through the downward refracting envi- ronment. ...............................101 B.1 Comparison of experimental and Bellhop-modelled time differences between the direct arrival, and surface and bottom reflections. 151 D.1 Comparison of the predicted and experimental delay times for the surface and bottom reflections. ....................162 vii E.1 Sediment parameters for geoacoustic modelling. ..........165 viii LIST OF FIGURES 2.1 Illustration of k-fold cross-validation ................ 12 2.2 Illustration of occurrence of positive and negative events with three example thresholds shown. ..................... 14 2.3 Confusion matrix for the two-class classification problem. ..... 15 2.4 Example ROC curves ........................ 16 2.5 Illustration of excellent accuracy and AUC, and poor accuracy but excellent AUC ............................ 17 3.1 Example spectrograms of real and synthetic bowhead and hump- back vocalizations. ......................... 20 3.2 Spectrograms of an example bowhead vocalization demonstrating the effects of signal denoising. ................... 22 3.3 Spectra of biogenic and synthetic whale vocalizations. ....... 24 3.4 Comparison of aural classifier decision regions for (a) biogenic and (b) synthetic bowhead and humpback whale vocalizations. ..... 26 3.5 Transmitting voltage response (TVR) curves for the ITC-2010 transducer and the complete amplifier and ITC-2010 transducer system ................................ 28 3.6 Spectra for full-band and bandpass filtered (a) bowhead and (b) humpback whale calls. ....................... 29 3.7 Results of training the classifier on (a) full band, and (b) bandpass filtered, biogenic bowhead and humpback vocalizations. ...... 30 4.1 (a) Map of the experimental location. (b) Map with ship tracks shown for both days of the experiment, including location of the recorders, CTD casts, and FFCPT measurements. ......... 35 4.2 Representation of the experimental setup. ............. 37 4.3 Ambient noise spectra for day 1 and day 2 of Gulf of Mexico experiment .............................. 41 4.4 Sediment type, in terms of the Robertson zone, obtained from Freefall Cone Penetrometer measurements. ............. 42 ix 4.5 Sound speed profiles observed (a)