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Affordable Robust Nonlinear Towed Hydrophone Arrays


Summary:  Passive acoustics has been increasingly used for population estimation during shipboard cetacean surveys conducted by NMFS Science Centers.  Towed linear arrays are well-developed but are limited in their ability to provide real-time 3D localization.  This is important for application to deep-diving species such as beaked whales, and for real-time localization of a single sound, which is important for line-transect surveys.  Development of a volumetric (nonlinear) towed hydrophone array can provide improved localization and, when used in combination with existing modular linear arrays, can provide instantaneous localization to sound sources using a single sound. These improvements are valuable not only for NMFS population surveys, but for detection of cetaceans during mitigation efforts (seismic industries, Navy) and have the potential to aid in search and rescue efforts (beacon detection/localization).


Current development of volumetric towed hydrophones show great potential, but have been limited by increased flow noise, tension, and instability at high speeds (Rankin, 2013b, Southall, et al., 2012).  NOAA Fisheries is requesting the development of nonlinear (volumetric) towed hydrophone array that can be used with current modular array systems developed by NMFS Science Centers (see Rankin et al. 2013a).


Project Goals:  The goal of this project is to develop a functioning nonlinear array using affordable materials and a modular design that will provide accurate 3D localization of marine mammals in real-time.  The modular design must be compatible with towed hydrophones developed by NMFS Science Centers (Rankin et al. 2013a). Extensive testing by NMFS has identified a pre-amplification system that works well with HTI 96min hydrophones and 12v power; deviation from this should be well tested and compatible with NMFS systems.  The prototypes should be robust and stable when towed at 10 knots behind a research vessel. Materials must be compatible with underwater acoustic detection (acoustically transparent and either negatively or neutrally buoyant).  The prototypes should consist of modular components such that repairs and replacement of individual components can be conducted by the users in field situations.


As many of the preliminary tests have already been conducted by NMFS Science Centers, we expect that development of an initial prototype can be conducted during Phase 1. We expect that Phase 2 will consist of repeated testing of modified prototypes until a stable and robust system is developed.  During commercial development phase, individual components should be available for replacement.


Phase I Activities and Expected Deliverables:

Activities include:

·         Identification of appropriate and cost-effective materials

·         Hydrodynamic modeling of prototype(s)

·         Development and initial testing of prototype(s)

Deliverables include:

·         Detailed report of initial prototype and results from initial modeling and testing


Phase II Activities and Expected Deliverables:

Activities include:

·         Field testing and Improvement of Prototype(s)

·         Integrating prototype with currently available software (Pamguard)

Deliverables include:

·         Fully functional pre-production prototype(s) with ancillary components necessary for further use on NMFS research vessels; and

·         Detailed report documenting the project, prototype design and results from hydrodynamic modeling and field testing

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