[MARMAM] PhD Thesis: The Significance of Passive Acoustic Array-Configurations on Sperm whale...

jonathan at underwateracoustic.com jonathan at underwateracoustic.com
Tue Feb 24 23:02:34 PST 2009


Dear all

This PhD Thesis was recently submitted and accepted by Heriot-Watt  
University, UK

Title: The Significance of Passive Acoustic Array-Configurations on  
Sperm whale Range Estimation when using the Hyperbolic Algorithm.


Abstract: In cetacean monitoring for population estimation,  
behavioural studies or mitigation, traditional visual observations are  
being augmented by the use of Passive Acoustic Monitoring (PAM)  
techniques that use the creature’s vocalisations for localisation.

The design of hydrophone configurations is evaluated for sperm whale  
(Physeter macrocephalus) range estimation to meet the requirements of  
the current mitigation regulations for a safety zone and behaviour  
research.

This thesis uses the Time Difference of Arrival (TDOA) of cetacean  
vocalisations with a three-dimensional hyperbolic localisation  
algorithm.  A MATLAB simulator has been developed to model  
array-configurations and to assess their performance in source range  
estimation for both homogeneous and non-homogeneous sound speed  
profiles (SSP).  The non-homogeneous medium is modelled on a Bellhop  
ray trace model, using data collected from the Gulf of Mexico.  The  
sperm whale clicks are chosen as an exemplar of a distinctive  
underwater sound.

The simulator is tested with a separate synthetic source generator  
which produced a set of TDOAs from a known source location. The  
performance in source range estimation for Square, Trapezium,  
Triangular, Shifted-pair and Y-shape geometries is tested.  The  
Y-shape geometry, with four elements and aperture-length of 120m, is  
the most accurate, giving an error of ±10m over slant ranges of 500m  
in a homogeneous medium, and 300m in a non-homogeneous medium.   
However, for towed array deployments, the Y-shape array is sensitive  
to angle-positioning-error when the geometry is seriously distorted.   
The Shifted-pair geometry overcomes these limits, performing an  
initial accuracy of ±30m when the vessel either moves in a straight  
line or turns to port or starboard. It constitutes a recommendable  
array-configuration for towed array deployments.

The thesis demonstrates that the number of receivers, the  
array-geometry and the array-aperture are important parameters to  
consider when designing and deploying a hydrophone array.  It is shown  
that certain array-configurations can significantly improve the  
accuracy of source range estimation.  Recommendations are made  
concerning preferred array-configurations for use with PAM systems.


For any pdf copies please do not hesitate to contact me at  
jonathan at underwateracoustic.com


Jonathan Vallarta, PhD

School of Engineering and Physical Sciences
Heriot-Watt University University
Edinburgh, UK







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