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Three pods of resident orca whales frequently vocalize near the shore of San Juan Island, WA. An array of eight hydrophones randomly spaced parallel to the shore records calls, echolocation clicks and background noise. Crosscorrelation is used to determine the time differences of sounds arriving at each hydrophone and singular value decomposition is used to reconstruct the location of each underwater sound source. To date (June 15, 2001), 85 separate calls and 245 echolocation clicks have been localized during 12 separate passes of these resident whales. Preliminary examination of these data show that whales echolocations usually come from one general location (+- 75m) while the pod of 5 to 20 whales are spread out over a much larger domain. When repeated calls are heard, they seem to emanate from one general location while the whales are spread out over a much larger domain. When calls and clicks are interspersed, usually the calls are not coming from the location where the clicks come from. During the course of the upcoming summer, I expect to gather about ten times more data so that statistical assessments of the locations and correlations between source locations may be made.
This hydrophone array is a part of the SeaSound project of the Whale Museum of Friday Harbor, WA. The array operates autonomously, triggering on interesting events and reconstructing their locations for close events and there bearing for events more than 1000 m distant. The hydrophone depths range from 3 to 18 m below mean sea level. The array is contained within a rectangle that is about 250 m long, parallel to the shore (facing the Haro Strait), and extends to a distance of about 30 m from the shore. The hydrophone locations have been determined by emitting chirps from an underwater speaker placed at many different locations near the array and then determining the best estimate of the hydrophone locations using simulated annealing.
