Ocean Seismo-Acoustics: Low-Frequency Underwater AcousticsTuncay Akal, J.M. Berkson 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. |
Contents
Sound Pulse Propagation in a Weakly Range | 1 |
Intrinsic Modes in a WedgeShaped Ocean with | 11 |
A Greens Function Method for OneWay Wave | 21 |
Copyright | |
80 other sections not shown
Other editions - View all
Ocean Seismo-Acoustics: Low-Frequency Underwater Acoustics T. Akal,J.M. Berkson Limited preview - 2013 |
Ocean Seismo-Acoustics: Low-Frequency Underwater Acoustics T. Akal,J.M. Berkson No preview available - 2012 |
Common terms and phrases
acoustic field acoustic propagation ambient noise amplitude approximately array arrival attenuation backscattering bathymetry beam beamforming boundary calculated coherence component compressional wave computed curves density effects elastic energy equation experiment experimental Figure fluid FREQUENCY Hz function geoacoustic geophone Geophysics gradient grazing angles Green's function group velocity horizontal hydrophone intensity fluctuations interaction interface waves internal waves inversion La Spezia levels linear low frequency marine sediments measurements medium modulus normal mode obtained ocean bottom P-wave parabolic parameters paths phase predicted pressure propagation loss properties pulse range dependent RANGE km ratio receiver reflection coefficient refraction scattering seafloor seamount sediment seismic seismometers sensors shallow water shear modulus shear wave shown in Fig signal slope solution sound speed sound speed gradient spectral spectrum subbottom surface theory towed transmission loss Underwater values vertical water column water depth wave propagation wave velocity wavenumber