Figure 5. Soniferous fish location device (SFL) with integrated optic and acoustic sensors to aid in the identification of unknown sound sources.
of sound source level (rather than just received sound source levels). Good data on sound source levels, and hence, detection ranges, are a prerequisite for broad-scale spatial mapping of animal distributions and habitat associations. Another important use of localization is to provide clues that can aid in the identification of unknown sounds. Currently most biological sounds recorded in marine and aquatic habitats are unknown due to the lack of study and a general lack of comprehensive sound catalogues. Localization provides clues such as whether the source is stationary or mobile, from single or multiple locations, near the bottom, in the water column, near the surface, nearby or far away, etc. Often this type of information can narrow down the field of possible sound source candidates at a given location. However, positive identification of sound sources requires either laboratory or field validation (i.e., actual observation of an animal calling). Because labwww.seadiscovery.com
oratory observations are often impractical or impossible, arrays that are integrated with other technologies that can provide field proof of the sound source identity will be vital to future passive acoustic research. The development of portable array systems is not as easy as it sounds due to the spatial scale required to localize on fish and marine invertebrate sounds, and to the requirements of marine ecologists. Typically fish vocalize at between 50 and 2000 Hz, and often between 100-500 Hz. Thus hydrophone spacing needs to be on the order of meters to 10's of meters, so small arrays typical of other acoustic tracking applications are not generally possible. Unfortunately, precise positioning of hydrophones in arrays at this spatial scale is often not possible due to depth or other logistical limitations, so methods of system self determination of array element locations are needed, even if only of relative distances among elements. Systems that can be quickly deployed, retrieved, and re-deployed
Marine Technology Reporter 45
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