Ocean Seismo-Acoustics

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.

Contenu

Propagation: Theoretical Developments.- Sound Pulse Propagation in a Weakly Range Dependent Shallow Ocean.- Intrinsic Modes in a Wedge-Shaped Ocean with Stratified Elastic Bottom.- A Green's Function Method for One-Way Wave Propagation in a Range-Dependent Ocean Environment.- Factorization and Path Integration of the Helmholtz Equation: Numerical Algorithms.- Range Dependent Propagation Codes Based on Wave Field Factorization and Invariant Imbedding.- An Acoustic Reflectivity Method for Laterally Varying Layered Media.- A Vector Parabolic Equation Model for Elastic Propagation.- Influence of Bottom Refraction on the Propagation of Underwater Sound.- Bottom Interaction Effects on Normal Modes: an Algebraic Approach.- Gaussian Beams and 3-D Bottom Interacting Acoustic Systems.- Development of a Parabolic Approximation for the Computation of Propagation Loss in a Range-Dependent Environment.- Propagation: Modelling and Experiments.- Linear and Nonlinear Ocean Acoustic Propagation Models.- Modeling of Pulse Response Functions of Bottom Interacting Sound Using the Parabolic Equation Method.- A Study of Propagation Loss Dependence on Sediment Layer Thickness using the Fast Field Program.- Shear Wave Effects on Propagation to a Receiver in the Substrate.- Description and Some Results of the Operational Propagation Loss Model ALMOST (= Acoustic Loss Model for Operational Studies and Tasks).- Experimental Confirmation of Horizontal Refraction of Sound Propagation in a Wedge-like Ocean.- Acoustic Propagation over Large-Scale Linear Ocean Slopes.- Predicted Partitioning of VLF Acoustic Energy in a Range-Dependent Environment.- Experiments on Sound Propagation over Sloped Bottoms.- The Effect of Unconsolidated Sediment Rigidity on Low Frequency Acoustic Propagation.- A Propagation Anomaly Observed in the Barents Sea.- Long Range Low Frequency Propagation Measurements in Deep Water Using a Seismic Towed Array.- Some Characteristics of Virtual Modes in Shallow Water with High Speed Bottom.- The Deduction of Approximate Values of Sediment Depth from Propagation Loss Measurements.- Propagation: Fluctuations.- Range and Time Dependence of Acoustic Intensity Fluctuations.- Shallow Water Tomography.- Medium-Induced Low-Frequency Fluctuations in Acoustic Transmission Loss: Examples from Measurements in Selected Geographical Areas.- Wave Propagation in Anisotropic Media Using Born Series Through 4th Order.- Coupling of Acoustic Modes in the Ocean, A Comparison of Approximate Solutions.- Boundary Scattering.- Long Range, Low frequency Acoustic Backscattering: A Survey.- Directional Measurements of Low-Frequency Acoustic Backscattering from the Seafloor.- Seamount Height Estimation from Long-Range, Low Frequency Acoustic Backscatter.- An Acoustic Model for Bathymetric Scattering with Low-Frequency Applications.- Evaluation of Low-Frequency Bottom Backscattering Strength vs Grazing Angle by Means of Multiple Beamforming.- Near Grazing Propagation over a Low Roughness Hard Ocean Bottom.- Estimation of Ice Surface Scattering and Acoustic Attenuation in Arctic Sediments from Long-Range Propagation Data.- Low Frequency Attenuation in the Arctic Ocean.- Effect of Sub-Bottom Inhomogenieties on Shallow Water Spatial Coherence.- Mode Coupling from Subbottom Roughness.- Sediments: Seismo-Acoustic Waves and Geoacoustic Characteristics.- Acoustic Waves in Marine Sediments.- Pore Shape and the Biot-Stoll Model for Saturated Sediments.- Low-Frequency Anomalies in the Reflection Behaviour of Marine Sediments.- The Interaction of Low-Frequency Acoustic Waves with a One-Dimensional Random Sediment Model.- Propagator Matrix for Acoustic Wave Propagation through Anisotropic Porous Media.- Acoustic-to-Seismic Coupling at Porous Ground Surfaces.- Geotechnical Characteristics of the Sea Bed Related to Seismo-Acoustics.- Dynamic Properties of Marine Sediments.- Relationship between the Acoustical Characteristics of Deep Sea Sediments and their Physical Environment.- Low Frequency Measurements of the Acoustic Properties of Marine Sediments.- Spatial Variability of Surficial Shallow Water Sediment Geoacoustic Properties.- A Bottom Shear Modulus Profiler: Inverse Analysis of the Field Data on Wave-Induced Bottom Motion.- Seismo-Acoustic Waves: Propagation, Attenuation, and Inverse Techniques.- Estimation of Subsurface Parameters in Lossy Media.- Analysis of Ocean-Subbottom Seismograph (OSS) Data.- The Relative Amplitudes of Primary and Multiple Signals Refracted in the Ocean Crust.- The Propagation of Pn.- Effects and Consequences of Transverse Isotropy in the Seafloor.- Seismic Anisotropy in the Upper Crust at DSDP Site 504B.- A Broad-Band Study of Attenuation in Ocean Bottom Sediments.- On the Role of Bottom Interface Waves in Ocean Seismo-Acoustics: A Review.- Observations on Interface Waves and Low-Frequency Acoustic Propagation Over a Rough Granite Seabed.- A Comparison of Seismic and Hydroacoustic Measurements at Very Low Frequencies in Different Shallow Water Areas.- Interface Wave Studies on the Ligurian Shelf using an OBS Array: Experimental Results and Propagation Models.- A Study of Sea Floor Structure Using Ocean Bottom Shots and Receivers.- Shear Properties of Ocean Sediments Determined from Numerical Modelling of Scholte Wave Data.- The Determination of Geoacoustic Models in Shallow Water.- The Estimation of the Density, P-Wave, and S-Wave Speeds of the Top-Most Layer of Sediments, from Water Bottom Reflection Arrivals.- Effects of Upper Crustal Geoacoustic Parameters on Low Frequency Sound.- Evaluation of Experimental Techniques for Determining the Plane Wave Reflection Coefficient at the Sea Floor.- Seismo-Acoustic Noise.- A Study of Ocean and Seismic Noise at Infrasonic Frequencies.- Geo-Acoustic Noise Levels in a Deep Ocean Borehole.- Low Frequency Noise Fields and Signal Characteristics.- Time Dependence of Infrasonic Ambient Seafloor Noise on a Continental Shelf.- Infrasonic Attenuation and Ambient Noise.- Technology and New Approaches in Seismo-Acoustic Measurements.- Parametric Sources - Design Considerations in the Generation of Low-Frequency Signals.- The Postcritical Penetration of Low Frequency Parametric Beams through a Water-Sediment Interface.- The Use of Low and High Frequency Intensity Fluctuations in Sea-Bed Surface Classification.- Ocean Bottom Seismology: History and Cur…