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Introduction
Engineering efforts for the HIFT experiment consisted of a number of components. The
acoustic sources are specially designed for high power and low frequency. The ship used
to conduct the experiment had to be robust enough to withstand the extreme weather of
the Southern Ocean. A variety of hydrophone arrays, the acoustic receivers, were used
to study the acoustical signals. Finally, extensive research on signal processing was
conducted, both to craft an optimal collection of signals to transmit from the source and
to optimally process the received signals to glean the most information possible from them.
The acoustic sources
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HLF-4 acoustic sources was used to make the acoustic transmissions. In the course of
the experiment, several of the acoustic sources were destroyed by the effects of foul weather!
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HLF-4
The R/V Cory Chouest
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The R/V Cory Chouest preparing to go to sea.
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Arrays of hydrophones
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Some of the hydrophone arrays were deployed from a ship (left), others were bottom mounted (right). These
were arrays of many hydrophones that are used to resolve some of the spatial properties of the arriving signals.
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The portable single hydrophone system
One of the interesting aspects of this experiment was a collection of
cheap, portable receivers that were sent out to a variety of research groups
around the world. This instrument was designed and built at
the Applied Physics Laboratory at the University of Washington. APL hosted a few workshops
or two for the participants from around the world to get familiar with the devices,
The device was a orange disk buoy about 2-3 ft diameter with electronics/antenna in center,
and a hydrophone hanging down. The electronics were similar to a standard U.S. Navy
sonobuoy. One goal with these devices was to get the hydrophone into the sound channel, so a much
longer cable connecting hydrophone to the electronics was employed. This cable consisted of a coiled
black cable with hair fairing.
A photo of one of these receivers in action in the Indian Ocean can be
seen HERE.
Signal processing
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