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Creating Custom Acoustic Reference Beacons for NOAA
RJE International is working with the National Oceanic and Atmospheric Administration (NOAA), to create custom, long-life, underwater acoustic beacons. RJE was tasked with creating a sound source with a low enough frequency to be detected by the recording system (frequency <7kHz), and have a frequency bandwidth and an inter-pulse group interval long enough to not interfere with signals of interest (marine mammal vocalizations). These custom acoustic sound sources will serve as reference signals in calibrating localization errors on passive acoustic recorders in the Chukchi Sea.
The pingers supplied by RJE International will be used in the Chukchi Acoustic Oceanographic and Zooplankton (CHAOZ) study. The goal of the CHAOZ study is to document the general presence of bowhead, right, fin, gray, and other whales in areas of potential seismic, drilling, construction, and production activities using passive acoustic monitoring. To better understand the reaction of marine mammals to offshore industrial development, better documentation is needed to describe migratory pathways, feeding areas, and areas where breeding or birthing occur. Timing and location of whale migrations may play an important role in assessing where, when or how exploration or access to petroleum reserves may be conducted. Furthermore, extreme ice-retreat and climate warming in the western Arctic over the last decade will cause changes in species composition and distribution, evidenced already through local knowledge and opportunistic observations. Acoustic monitoring in the Chukchi Sea year-round for several years will provide a long-term assessment of the seasonal occurrence of large whales in this region and their response to environmental changes (Crance, 2010).
NOAA will be deploying three arrays of long-term acoustic recorders in the Chukchi Sea. Each array consists of 5 recorders spaced approximately 2-5 miles apart in a pentagonal shape. Each recorder mooring will consist of (a) a buoy, (b) a cable/chain, (c) the autonomous recording device, (d) an acoustic sonic release system, and (e) a heavy object to anchor the mooring. These recorders will record for 1.5 hours every 3 hours, at a sampling rate of ~ 16 kHz, for an entire year. The use of five recorders in each array allows for localization of calling whales, in addition acting as a safeguard in the event of a recorder failure. Each mooring will have one pinger, thus each array will have 5 pingers. The RJE pingers will be used as reference signals to calibrate the distance errors in localization calculations. The pingers will also serve to guide recovery of the moorings if the acoustic releases fail and dragging is necessary (Crance, 2010).
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