Estimation of Ice Surface Scattering and Acoustic Attenuation in Arctic Sediments from Long-Range Propagation Data PDF Download
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Author: G. L. Duckworth Publisher: ISBN: Category : Languages : en Pages : 14
Book Description
A single explosive shot at a range of 341.3 km in the Pole Abyssal Plain of the Arctic Ocean is used to assess the components of propagation loss for this region. The acoustic energy propagated between a satellite ice camp and the Fram II ice station in a water column of nearly uniform depth. Much of the observed energy interacted with the upper 200 meters of sediments along a path which was nearly parallel to the Arctic Mid-Ocean Ridge. In addition, the upward refracting sound channel of the Arctic Ocean also caused the observed energy to interact extensively with the ice canopy, which was contiguous over the entire path. The deterministic lateral homogeneity of the bathymetry and sediments, and the statistical lateral homogeneity of the ice canopy in this region allow us to attempt to separate the effects of geometrical spreading, ice surface scattering, and effective sediment compressional wave attenuation. The primary data for this work are observations of the signal from a 25.8 kg explosive charge received on a 24 channel two-dimensional hydrophone array with a 1 km aperture. The data are inadequate to resolve attenuation at depth, but provide an estimate for frequency independent Q of 200 to 300 for the upper 200 meters of the sediments and a dependency of surface scattering on frequency over the 5-50 Hz band. It is shown that partially coherent summation of the surface multipaths is required to predict the observations. (RRH).
Author: G. L. Duckworth Publisher: ISBN: Category : Languages : en Pages : 14
Book Description
A single explosive shot at a range of 341.3 km in the Pole Abyssal Plain of the Arctic Ocean is used to assess the components of propagation loss for this region. The acoustic energy propagated between a satellite ice camp and the Fram II ice station in a water column of nearly uniform depth. Much of the observed energy interacted with the upper 200 meters of sediments along a path which was nearly parallel to the Arctic Mid-Ocean Ridge. In addition, the upward refracting sound channel of the Arctic Ocean also caused the observed energy to interact extensively with the ice canopy, which was contiguous over the entire path. The deterministic lateral homogeneity of the bathymetry and sediments, and the statistical lateral homogeneity of the ice canopy in this region allow us to attempt to separate the effects of geometrical spreading, ice surface scattering, and effective sediment compressional wave attenuation. The primary data for this work are observations of the signal from a 25.8 kg explosive charge received on a 24 channel two-dimensional hydrophone array with a 1 km aperture. The data are inadequate to resolve attenuation at depth, but provide an estimate for frequency independent Q of 200 to 300 for the upper 200 meters of the sediments and a dependency of surface scattering on frequency over the 5-50 Hz band. It is shown that partially coherent summation of the surface multipaths is required to predict the observations. (RRH).
Author: T. Akal Publisher: Springer Science & Business Media ISBN: 1461322014 Category : Science Languages : en Pages : 898
Book Description
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.
Author: R. H. Mellen Publisher: ISBN: Category : Languages : en Pages : 36
Book Description
Underwater acoustic propagation in the Arctic Ocean is characterized by a refractive surface-channel with a rough boundary. Acoustic scattering estimates, based on free-surface theory, have proven low by more than a factor of two in forward-scatter loss and low by 20 dB or more in backscatter strength. Failure to account for either attenuation or backscattering indicates that impedance effects must be involved. The ice layer is modeled as a uniform elastic solid. Perturbation analysis shows scattering from slopes as well as displacements. Displacements produce piston-like reradiation in addition to the usual vertical-dipole type associated with free surfaces. The 'rocking' horizontal dipole produced by slopes is evidently a significant mechanism at the lower frequencies. However, estimates of both attenuation and backscatter strength are much too low compared with experimental data. Keywords: Acoustic attenuation; Ice-water interface slope; Acoustic reflectivity; Underice roughness, Acoustic velocity; Low-frequency.
Author: R. R. Greene Publisher: ISBN: Category : Languages : en Pages : 41
Book Description
Acoustic propagation in the Arctic is intimately related to the structure of surface pack ice. In this paper, reflection loss and transmission loss are calculated based upon statistical models of ice roughness. Statistical models of ice ridges are introduced and techniques for estimating the roughness spectrum of ridged surfaces are developed. Next, a model for estimating the mean reflection loss is introduced. The reflection loss formulas are based on the statistical models for roughness. Transmission loss calculations using High-Angle parabolic equation (ARCHAPE) in a simulated Arctic environment are compared with data. The results demonstrate that rough surface scattering from random-depth ice keel structures can account for the observed rate of transmission loss in the Arctic. Keywords include: Acoustic Scattering, and Propagation loss.
Author: Paul C. Etter Publisher: CRC Press ISBN: 1351679724 Category : Technology & Engineering Languages : en Pages : 639
Book Description
This newest edition adds new material to all chapters, especially in mathematical propagation models and special applications and inverse techniques. It has updated environmental-acoustic data in companion tables and core summary tables with the latest underwater acoustic propagation, noise, reverberation, and sonar performance models. Additionally
Author: G. L. Duckworth
Author: G. L. Duckworth
Author: T. Akal
Author: R. H. Mellen
Author: A. Lara-Sáenz
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Author: R. R. Greene
Author: Paul C. Etter
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