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EARS is an undersea sound recording system developed by the
United States Naval Oceanographic Office. The system
consists of a data-logger assembly and hydrophones, with preamplifiers
situated near the cable-mounted hydrophones. LADC has ten
data-loggers and four-channel hydrophone cables in lengths from 50- to
300-m. Omni Technologies, Inc, constructed the system
used by the LADC consortium under a cooperative agreement with the Navy.
An EARS mooring consists of at least one data-logger and hydrophone
cable (though multiple data-loggers may be employed with several
hydrophone cables), an anchor, an acoustic release system for
retrieval,
flotation devices, connecting hardware, and lengths of cable to
ensure desired phone placement. A representative mooring is
depicted schematically in Figure 1.
Figure 1: A typical EARS mooring (courtesy Dr. Joal Newcomb).
This particular mooring has three hydrophone cables and four
data-loggers (labeled as EARS buoys), two of which are mounted in
parallel as a unit. An iron anchor secures the assembly to the
seafloor, and flotation devices (yellow) are at top and distributed
along the mooring's length. When a system is deployed it is
assembled aboard a research vessel. The array is streamed out
"top first" behind the vessel, leaving the anchor on board. As
the ship steams toward the deployment point the array is trailing
astern. The anchor is released at the deployment location,
carrying the mooring with it. Figure 2 shows a mooring assembled
on deck aboard R/V Longhorn, ready for deployment in the Gulf of Mexico.
Figure 2: Mooring assembled aboard R/V Longhorn, November 2005.
Figure 2 is a view over the stern of R/V Longhorn. The stern-most
floats (upper right in figure) are at the top of the mooring, and the
anchor is at the stern, across the deck from them. One of
the data-logger assemblies is clearly visible in the foreground, next
to several spare anchors. The hydrophone array cables are coiled
in three boxes, one of which is just visible in the foreground.
The large orange floats house four-channel Acoustic Doppler
Current Profilers (ADCP's). The dual acoustic release assembly is
situated between the ADCP assemblies, resting on a tire. (In this
survey the ADCP's were to be used in conjunction with positioning
transponders to monitor the shape of the array and better localize the
hydrophones.) During deployment the array was streamed out
astern, starting with the floats at upper right, ultimately leaving
only the anchor secured from the stern A-frame via a quick-release
shackle. The anchor was released at the drop point, deploying the
array.
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