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In 1983 in area of Copper-Nickel rich manganese nodules at 14 deg 40 min N, 126 deg 25 min W (site 'E) was intensively studied with the Deep-Tow of the Scripps Institution of Oceanography, and 16 box cores were collected. Deep-Tow studies of the Thirtymile-Bank off the California Coast and the deep sea at the foot of the Patton Escarpment followed. The nodule coverage at site 'E varies from 0% to 80%. The nodule sizes vary between 1 and 13 cm. The nodule size distributions are best modeled by a Gaussian distribution. The three main nodule axes are related to each other at 1:0.8:0.5. The average density of individual nodules is 2.0 + or - 0.04 g/cu cm and the volumes increase on the average with the 2.8 power of the third root of the product of the three radii. Changes of the thickness of the upper acoustic unit of the sediment column correlate with changes in nodule coverage and concentration. The acoustic backscatter has been measured for frequencies of 4.5, 9, 15, 28, 60, 112 and 163 kHz and grazing angles from normal incidence to 5 degrees. The backscatter increases as the square of the frequency for sediments.
Seafloor investigation has long been a feature of not only seismology but also of acoustics. Indeed it was acoustics that produced depth sounders, giving us the first capability of producing both global and local maps of the seafloor. Subsequently, better instrumentation and techniques led to a clearer, more quantitative picture of the seabed itself, which stimulated new hypotheses such as seafloor spreading through the availability of more reliable data on sediment thickness over ocean basins and other bottom features. Geologists and geophysicists have used both acoustic and seismic methods to study the seabed by considering the propagation of signals arising from both natural seismic events and man-made impulsive sources. Although significant advances have been made in instrumentation, such as long towed geophysical arrays, ai r guns and ocean bot tom seismometers, the pic ture of the seafloor is still far from complete. Underwater acoustics concerns itself today with the phenomena of propagation and noise at frequencies and ranges that require an understanding of acoustic interaction at both of its boundaries, the sea surface and seafloor, over depths ranging from tens to thousands of meters. Much of the earlier higher frequency (>1 kHz) work included the characterization of the seafloor in regimes of reflection coefficients which were empirically derived from surveys. The results of these studies met with only limited success, confined as they were to those areas where survey data existed and lacking a physical understanding of the processes of reflection and scattering.
Measurements were made of sound speed and attenuation in marine sediments at 15, 30, and 60kHz by means of in situ acoustic probe instrumentation in conjunction with CURV II. These experiments were conducted in silty sand and sandy silt Continental Shelf areas of the Santa Barbara Channel, California. The main conclusions are: (1) attenuation was found to be about 3, 10, and 20 dB per meter at 15, 30, and 60 kHz, respectively; (2) for the attenuation equation, alpha = K(f to the nth power) (where alpha is sound attenuation in dB per meter, K is a dimensional material parameter, and f is frequency in kHz), the exponent, n, was found to be about 1.2, and K varied from approximately 0.1 to 0.2; (3) no significant sound-speed dispersion was found, in agreement with many other investigations; and (4) individual acoustic measurements made in close proximity to one another in a nominally homogeneous bottom can vary appreciably, although their average values may be in close agreement. (Author).
The acoustic attenuation in ocean sediments is a major loss mechanism for low frequency acoustic propagation in shallow water regions. Analysis of measured propagation in these regions has generally included estimates of the attenuation in the sediment, without consideration of the variations in attenuation as a function of depth. It will be shown that these variations can have a significant impact on the standard estimates. A new procedure is then developed which provides estimates of the attenuation as a function of depth. This procedure is used to obtain attenuation depth profiles in three shallow water regions. These estimated profiles present characteristics observed in laboratory and in situ measurements
This book honors the career of Professor Elizabeth Gierlowski-Kordesch who was a pioneer and leader in the field of limnogeology since the 1980s. Her work was instrumental in guiding students and professionals in the field until her untimely death in 2016. This collection of chapters was written by her colleagues and students and recognize the important role that Professor Gierlowski-Kordesch had in advancing the field of limnogeology. The chapters show the breadth of her reach as these have been contributed from virtually every continent. This book will be a primary reference for scientists, professionals and graduate students who are interested in the latest advances in limnogeologic processes and basin descriptions in North and South America, Europe, Africa, and China. *Free supplementary material available online for chapters 3,11,12 and 13. Access by searching for the book on link.springer.com
An experimental system has been developed that makes possible the in situ collection of acoustic data in marine sediments, with greater convenience and accuracy than has been obtainable by laboratory analysis of bottom core samples. The feasibility of the system, operating in conjunction with the NUC Cable-Controlled Underwater Research Vehicle (CURV II), has been demonstrated. System capabilities are discussed.
Cold-water coral ecosystems figure the formation of large seabed structures such as reefs and giant carbonate mounds; they represent unexplored paleo-environmental archives of earth history. Like their tropical cousins, cold-water coral ecosystems harbour rich species diversity. For this volume, key institutions in cold-water coral research have contributed 62 state-of-the-art articles on topics from geology and oceanography to biology and conservation, with some impressive underwater images.