Greater Boston Chapter
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Greater Boston Chapter |
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DESCRIPTION: Musicians and architects generally consider acoustic echoes a nuisance, but to ocean acousticians they provide one of the most robust means for exploring the ocean. In this presentation, acoustic reflections are used to study two different topics: acoustic inversion of the potential interior ocean of Jupiter's moon Europa, and acoustic tracking of diving sperm whales in the Gulf of Mexico.The measurement of relative reflection times is being used in computational simulations of acoustic propagation inside Jupiter's moon Europa, using acoustic propagation codes (OASES) originally developed for modeling the Arctic ocean, under the leadership of Prof. Nick Makris, of the ocean engineering department at MIT. Recent gravitational and magnetic measurements of Europa have provided strong circumstantial evidence that an ice layer up to 100 km thick may exist on this moon, with the possibility that a portion of this layer may be a liquid ocean. Photographs of the surface suggest that natural ambient noise sources between 0.1 and 100 Hz might exist, due to diurnal tidal flexing of the ice shell. Simulations of seismic fractures at the surface, ice base, and ocean bottom indicate that acoustic reflections from the ice/space, ice/water and water/mantle interfaces can be seperated in time by a geophone on the surface of the moon, which could be used to map out the dimensions of the interior ocean. In addition, similar techniques are being applied to the study of tracking whales. Sperm whales produce 10 ms pulses, known as 'clicks'. During a July 2000 cruise in the Gulf of Mexico multiple reflections from a single click were recorded on two elements of a towed hydrophone array, deployed at an unknown depth and tilt behind the NOAA vessel Gordon Gunter. By measuring the relative arrival times and array bearings of the reflections, three-dimensional profiles of three diving animals were obtained, and the array position recovered. The whales' depth estimates were then used to demonstrate that the interval between clicks was closely related to the whale's distance above the ocean floor. The measurements also showed depth-dependent features in the spectral structure of the clicks, as well as evidence for signal directivity. |
Underwater Acoustics (Tracking Sperm Whales) Using Simple Acoustic Inversion Methods - Aaron Thode, Michelle Zanolin and Sunwoong Lee | |
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Please feel welcome to join the group at 5:30 PM for a casual dinner at the Cactus Club (at the corner of Hereford and Boylston across from the Hynes Convention Center). | |
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Berklee College of Music 1140 Boylston Ave. Boston, MA The building is located one block west of intersection with Massachusetts Ave. on the corner of Hemingway St. (See the map below) | |
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