SpringerBriefs in Oceanography – serie

Offshore drilling and constructions require exact knowledge of the geophysical properties of the seabed and sub-seabed, as unexpected objects can slow down or halt projects. This book presents the state-of-the-art in acoustic exploration of the seabed and sub-seabed, from initial designs in the 1980s to commercial contracting and operation of the Acoustic Corer™ in the last decade. The Acoustic Corer™ is a high-definition commercial acoustic sub-bottom imaging system, producing an “acoustic core” within which sub-seabed sedimentary characteristics and discrete buried objects larger than 0.5 m can be identified and mapped. It makes use of the innovative JYG-cross design, inspired by seismic reflection and uses Synthetic Aperture Sonar (SAS) multi-angle scattering in and within the seabed to deliver unprecedented imagery. This book was written by the inventor of these concepts, a known specialist in seabed acoustics, with help from an experienced academic and author. It is intended first and foremost as a “how-to” guide for offshore industries looking at techniques to make the installation of different types of structures safe and efficient.

This Technical Report presents the outcome of a Working Group that was established to determine broadly applicable sound exposure guidelines for fishes and sea turtles. After consideration of the diversity of fish and sea turtles, guidelines were developed for broad groups of animals, defined by the way they detect sound. Different sound sources were considered in terms of their acoustic characteristics and appropriate metrics defined for measurement of the received levels. The resultant sound exposure guidelines are presented in a set of tables. In some cases numerical guidelines are provided, expressed in appropriate metrics. When there were insufficient data to support numerical values, the relative likelihood of effects occurring was evaluated, although the actual likelihood of effects depends on the received level. These sound exposure guidelines, which are based on the best scientific information at the time of writing, should be treated as interim. The expectation is that with more research the guidelines can be refined and more cells in the tables completed. Recommendations are put forward defining the research requirements of highest priority for extending these interim exposure guidelines.

This book presents a concise description of the acoustics of ocean sediment acoustics, including the latest developments that address the discrepancies between theoretical models and experimental measurements. This work should be of interest to ocean acoustic engineers and physicists, as well as graduate students and course instructors. The seabed is neither a liquid nor a solid, but a fluid saturated porous material that obeys the wave equations of a poroelastic medium, which are significantly more complicated than the equations of either a liquid or a solid.This volume presents a model of seabed acoustics with input parameters that allow the model to cover a wide range of sediment types.  The author includes example reflection and transmission curves which may be used as typical for a range of sediment types. The contents of this book will allow the reader to understand the physical processes involved in the reflection, propagation, and attenuation of sound and shear waves in ocean sediments and to model the acoustic properties for a wide range of applications.

As such, geoscientists are called upon to analyze the coastal hazards by anticipating the changes in and impacts of extreme weather hazards on the Bay of Bengal coasts as a result of global climate change and local sea-level change.