It is a lot more difficult than one might imagine to determine what noises affect marine mammals. And it might surprise you to find out how much time, effort, money, and creativity are being invested in finding out. Aaron Thode a researcher at the Scripps Institution of Oceanography talked about the work he is doing in marine mammal acoustics at a conference held in Houston October 28-30, 2008. The goal of Thode’s project, funded by the E&P Sound & Marine Life JIP, was to determine if whales identified by towed acoustic arrays were to the left or right of the towing vessel. According to Thode, passive acoustic towed array systems are a popular configuration for current marine mammal mitigation efforts. Typical systems use an array of linearly arranged hydrophones to measure the difference in arrival times of an acoustic pressure wave across the array. This measurement can be converted into a bearing estimate. The problem, Thode explained, is that the phone cannot determine the originating direction of the sound. “Using single linear array, it is impossible to tell if a sound is coming from port or starboard.” Technology for measuring the acoustic particle velocity of a sound wave has existed for 50 years, and directional sensors have been used for 30 years, Thode said, but because the sensors are very sensitive to vibration, traditional sensors are not suitable for towed arrays. Newly introduced technology, however, has eliminated that problem. The new sensor, Thode said, “measures pressure and velocity as well as pitch, roll, and yaw,” enabling it to orient itself to enable accurate readings to determine if marine mammals are to the right or left of the towing vessel. Thode conducted a test of a 1.5-m (5-ft) vector sensor towed array module off the coast of Sitka, AK, in July 2008. That test, Thode said, demonstrated the system’s ability to detect and resolve the bearing of sperm whale sounds. The system also demonstrated what Thode called “an unexpected ability” to eliminate noise contamination from the towing vessel. This project officially concludes in November, 2008, but other similar projects to protect marine life are ongoing, and they are backed by the E&P industry by such companies as Anadarko, BG Group, BHP Billiton, BP, Chevron, ConocoPhillips, Eni, ExxonMobil, IAGC, Santos, Shell, StatoilHydro, Total, and Woodside. When detractors of the oil and gas industry complain that marine life is be threatened or harmed by exploration activity, it might be a good idea to point them in the direction of this JIP.
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