in a variety of habitats and environmental conditions are desired. A particularly desirable array system would provide an integrated display of the array configuration (array element locations), with a GIS display of bathymetry, water temperature and other available environmental variables, together with real-time locations of both known and unknown sounds. Such a system would top my Christmas wish list!
Sound Source Identification
ful new tool for locating animals and observing their behavior remotely and over long time periods. For the marine technology industry, passive acoustics promise both exciting challenges in hardware and software development and in the integration of different technologies, but also great commercial opportunities due to its usefulness in a wide range of applications and disciplines.
As previously mentioned, one of the most important, and exciting uses of hydrophone array systems is for identification of unknown sound sources. In some limited cases, such as on coral reefs where visibility is good, source identification can be achieved by mounting underwater video cameras on the array. Even here, though, better integration of acoustic and video data is needed. Further, video systems require the use of artificial lights that can greatly limit deployment options due to high power requirements. More importantly, artificial lights will often have a strong influence on animal behavior and many animals may not exhibit vocal behavior in their vicinity. In these cases, systems that integrate other observation technologies such as acoustic imaging have the greatest promise. But so far we have been talking about fixed arrays and even acoustic imaging has only a limited range. How do we determine the identity of unknown sounds over larger spatial scales? One option is to use location data derived from an array to guide an ROV, AUV, UUV, Glider or other mobile gear to the sound source location where they can utilize integrated optic, sonar, and acoustic imaging sensors to identify the source. The ultimate technology would be the development of an autonomous "Soniferous fish Locator" (SFL) device as originally envisioned by the late Joe Blue and myself. The SFL could be mounted on various mobile platforms, and could be used to locate sound sources in one of two ways depending on the sound source characteristics. In some cases, the SFL could locate the sound and directly guide the mobile platform to the source location. In other cases, the SFL could allow the platform to home-in on the sound source through the process of null steering. In either case, the SFL technology could open up an exciting new field of underwater exploration.
Conclusion
About the Author
Passive acoustic technology promises to become an important component of many fields of marine science in the coming decades. It will be particularly important to the exploration of the seas in that it can provide a power46 MTR
Dr. Rountree has over 20 years experience as a marine ecologist, and has managed multidiciplinary estuarine and fisheries programs for the National Marine Fisheries Service and the University of Massachusetts. In recently years he has become recognized as an international leader in the development of passive acoustic technology applications to fisheries. He recently founded a small consulting firm, Marine Ecology and Technology Applications, Inc., in East Falmouth, Massachusetts which conducts basic research, provides public education and outreach, and provides consultation to the technology industry on applications of advanced technologies in the fields of marine ecology and fisheries. He maintains an extensive research web site at http://www.fishecology.org. His business web site is
http://www.marineecologyandtechnology.com November/December 2008
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