Near Canopy Arctic Acoustic Backscattering Study
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| Total Pages | : 0 |
| Release | : 1994 |
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We collected under-ice backscattering data with a low frequency (400 Hz), spatially diverse, transmitting and receiving array during the ONR SIMI project in Spring '94. The experiment, termed IBEX (Ice Backscattering Experiment) was based on the idea that such arrays of sources and receivers can be used to make images of backscattered sound when the geometry is very well known. The data has been processed using interferometric (time delay) imaging to localize high scattering regions. The measurements were made in two locations; one directed at imaging a large ridge, the other directed at imaging an 1000 m diameter expanse of a single floe. The measurements were carried out using several pulse types. We also operated a hyperbolic noise event tracking system to locate ice-cracking events and initiate an imaging sequence. The noise levels and activity were so low during the experiment period, that this feature could not be utilized. The ridge imaging was a collaborative effort with the MIT Group under the direction of Hendrik Schmidt. We have not received the MIT data for the combined effort at this writing.
| Author | : I. Dyer |
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| Total Pages | : 12 |
| Release | : 1982 |
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Sound waves created by high-energy explosives were used to measure reverberation and backscattering in the Arctic Ocean. From an ice camp in the Beaufort Sea, signals were backscattered from the continental margin and other major features of the basin. An acoustic array was used to analyze the signals in azimuth. Based on these data we constructed charts of normalized backscatter level, which can be compared with known topography of the Arctic Ocean. Resolution of this remote sensing technique for our experimental conditions (analysis frequency, 9 Hz; averaging time, 20 s; array size, 600 x 600 m) is about 8 deg in azimuth, 15 km in radial extent, and 1 km in depth. We obtained interpretable signals out to 2700 km. For 1000 km or less, the backscatter charts provide continuous coverage of the margins and major submerged features. Strong returns from about 73.2 deg N, 139.0 deg W indicate one or more prominent features that many contemporary topographic charts do not show, but which we believe to be real. Other strong returns are evident from the Northwind Escarpment and from the continental slopes of Alaska and the Canadian Archipelago. Via a backscatter model, we estimate the roughness product (rms height times correlation radius) of these features to be about 4500 sq m on average. Reprints (EDC).
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| Total Pages | : 704 |
| Release | : 1995 |
| Genre | : Aeronautics |
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| Author | : Patrick L. Denny |
| Publisher | : |
| Total Pages | : 131 |
| Release | : 1986 |
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When low frequency underwater sound interacts with the Arctic ice cover, not only will it be reflected from the plane and scattered in all directions from roughness elements, but it will also be diffracted at leads and reradiated from flexural waves in the ice. These phenomena have been studied in an anechoic tank by pulse transmission from an underwater point source to a series of large floating acrylic plate models, each representing a different type of ice cover. The flexural wave speed, the plate and lead dimensions and the acoustic roughness are accurately scaled, and the specific acoustic impedance contrast is approximately modeled by the selection of the acrylic material. The physical contributors to the gross reflection coefficient and backscattering strength are identified and compared for models of a plane ice layer, an Arctic ice pressure ridge, edges of leads, and a rubble field of ice. Keywords: Underwater Acoustics; Scatter, Backscatter; Arctic Ice; Reflection Coefficient; Flexural Waves; Theses.
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| Total Pages | : 332 |
| Release | : 1973 |
| Genre | : Arctic regions |
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One issue each year devoted to the annual report.
| Author | : Lucy Jane Kulbago |
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| Total Pages | : 0 |
| Release | : 1994 |
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| Total Pages | : 914 |
| Release | : 1992 |
| Genre | : Physics |
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| Author | : Wade H. Shafer |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 411 |
| Release | : 2012-12-06 |
| Genre | : Science |
| ISBN | : 1461305993 |
Masters Theses in the Pure and Applied Sciences was first conceived, published, and disseminated by the Center for Information and Numerical Data Analysis and Synthesis (CINDAS) * at Purdue University in 1 957, starting its coverage of theses with the academic year 1955. Beginning with Volume 13, the printing and dissemination phases of the activity were transferred to University Microfilms/Xerox of Ann Arbor, Michigan, with the thought that such an arrangement would be more beneficial to the academic and general scientific and technical community. After five years of this joint undertaking we had concluded that it was in the interest of all con cerned if the printing and distribution of the volumes were handled by an interna tional publishing house to assure improved service and broader dissemination. Hence, starting with Volume 18, Masters Theses in the Pure and Applied Sciences has been disseminated on a worldwide basis by Plenum Publishing Cor poration of New York, and in the same year the coverage was broadened to include Canadian universities. All back issues can also be ordered from Plenum. We have reported in Volume 32 (thesis year 1987) a total of 12,483 theses titles from 22 Canadian and 176 United States universities. We are sure that this broader base for these titles reported will greatly enhance the value of this important annual reference work. While Volume 32 reports theses submitted in 1987, on occasion, certain univer sities do report theses submitted in previous years but not reported at the time.
| Author | : Herman Medwin |
| Publisher | : Academic Press |
| Total Pages | : 739 |
| Release | : 1997-11-05 |
| Genre | : Science |
| ISBN | : 0080532160 |
The developments in the field of ocean acoustics over recent years make this book an important reference for specialists in acoustics, oceanography, marine biology, and related fields. Fundamentals of Acoustical Oceanography also encourages a new generation of scientists, engineers, and entrepreneurs to apply the modern methods of acoustical physics to probe the unknown sea. The book is an authoritative, modern text with examples and exercises. It contains techniques to solve the direct problems, solutions of inverse problems, and an extensive bibliography from the earliest use of sound in the sea to present references.Written by internationally recognized scientists, the book provides background to measure ocean parameters and processes, find life and objects in the sea, communicate underwater, and survey the boundaries of the sea. Fundamentals of Acoustical Oceanography explains principles of underwater sound propagation, and describes how both actively probing sonars and passively listening hydrophones can reveal what the eye cannot see over vast ranges of the turbid ocean. This book demonstrates how to use acoustical remote sensing, variations in sound transmission, in situ acoustical measurements, and computer and laboratory models to identify the physical and biological parameters and processes in the sea.* Offers an integrated, modern approach to passive and active underwater acoustics* Contains many examples of laboratory scale models of ocean-acoustic environments, as well as descriptions of experiments at sea* Covers remote sensing of marine life and the seafloor* Includes signal processing of ocean sounds, physical and biological noises at sea, and inversions* resents sound sources, receivers, and calibration* Explains high intensities; explosive waves, parametric sources, cavitation, shock waves, and streaming* Covers microbubbles from breaking waves, rainfall, dispersion, and attenuation* Describes sound propagation along ray paths and caustics* Presents sound transmissions and normal mode methods in ocean waveguides
| Author | : J.A. Dowdeswell |
| Publisher | : Geological Society of London |
| Total Pages | : 631 |
| Release | : 2016-12-16 |
| Genre | : Science |
| ISBN | : 1786202689 |
New geophysical techniques (multibeam echo sounding and 3D seismics) have revolutionized high-resolution imaging of the modern seafloor and palaeo-shelf surfaces in Arctic and Antarctic waters, generating vast quantities of data and novel insights into sedimentary architecture and past environmental conditions. The Atlas of Submarine Glacial Landforms is a comprehensive and timely summary of the current state of knowledge of these high-latitude glacier-influenced systems. The Atlas presents over 180 contributions describing, illustrating and discussing the full variability of landforms found on the high-latitude glacier-influenced seafloor, from fjords and continental shelves to the continental slope, rise and deep-sea basins beyond. The distribution and geometry of these submarine landforms provide key information on past ice-sheet extent and the direction and nature of ice flow and dynamics. The papers discuss individual seafloor landforms, landform assemblages and entire landsystems from relatively mild to extreme glacimarine climatic settings and on timescales from the modern margins of tidewater glaciers, through Quaternary examples to ancient glaciations in the Late Ordovician.
