ware for field recording and data processing. Like other observational technologies, passive acoustics often produce a daunting amount of digital data that must be processed either in real time or during post processing. To be sure, investigators around the world have had various amounts of success developing automatic detection algorithms for marine mammals and fishes, but efforts have not yet been translated to technologies readily available to others. In addition, we need much more robust programs capable of recognizing and classifying both known and unknown biological sounds. It is important to note that often the temporal and spatial context of a detected sound is just as important as the sound itself. Therefore, auto-detection programs should provide information on the relative and absolute time reference for each sound. In addition programs that can automatically provide statistical data on sounds, such as duration, dominant frequency, pulse rate, pulse width, pulse number, etc., are much desired. The ability to compile large sample sizes for these parameters is vital to ecological studies. Software development is a challenging area of passive acoustic research, but promises great intellectual and commercial rewards. The development of advanced passive acoustic instrumentation beyond existing systems currently used by a few laboratories for specialized studies, into robust systems that can be made available off-the-shelf for a variety of uses is dependent on the development of more robust acoustic software.
Shore-based Passive Acoustic Systems
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!
The "bread-n-butter" technology needed for further expansion of the field will be low-cost, hand-held systems that will become a standard component of academic, industry and government research and monitoring programs right alongside seine nets and environmental probes. However, currently investigators have to cobble together sound digitizing and recording equipment never intended for field use, let alone use around water. Unfortunately, these make-shift systems lack many specific components or options that investigators quickly discover needing upon attempting to conduct a passive acoustic survey. Among the most important needs are integrated systems (hydrophones, digitizer, recording system and software) that run off of a single power source, can be used in various lighting conditions, have real-time monitoring and playback capabilities, and have accurate and calibrated gain control options. Just as importantly we need specialized software designed for field use in rugged marine and aquatic habitats. Currently there are many
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Figure 3. A large composite fixed array composed of multiple modular arrays to allow localization of sounds on different spatial scales. Marine Technology Reporter 43
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