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Acoustic wave propagation in liquid media containing many air-filled bubbles is ab initio considered. A self-consistent method is used to derive a set of coupled equations describing rigorously the multiple scattering of waves in such media. The wave transmission and backscattering are then solved exactly. The numerical results indicate localization of acoustic waves in a range of frequency.[S0031-9007(98)05787-1]

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The aim of this community white paper is to make recommendations for a glider component of a global ocean observing system. We first recommend the adoption of an Argo-like data system for gliders. Then, we argue that combining glider deployments with the other components (ships, moorings, floats and satellites) will considerably enhance our capacity for observing the ocean by filling gaps left by the other observing systems. Gliders could be deployed to sample most of the western and eastern boundary circulations and the regional seas (around 20 basins in the world) which are not well covered by the present global ocean observing system and in the vicinity of fixed point time series stations. These plans already involve people scattered around the world in Australia, Canada, Cyprus, France, Germany, Italy, Norway, Spain, UK, and the USA, and will certainly expand to many other countries. A rough estimate of resources required is about 13M$/Euro for ~20+ gliders permanently at sea during five years in the world ocean, based on present scientific infrastructures.

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The value of global (e.g. altimetry, satellite sea-surface temperature, Argo) and regional (e.g. radars, gliders, instrumented mammals, airborne profiles and biogeochemical) observation-types for monitoring the mesoscale ocean circulation and biogeochemistry is demonstrated using a suite of global and regional prediction systems and remotely-sensed data. A range of techniques is used to demonstrate the value of different observation-types to regional systems and the benefit of high-resolution and adaptive sampling for monitoring the mesoscale circulation. The techniques include Observing System Experiments, Observing System Simulation Experiments, adjoint sensitivities, representer matrix spectrum, observation footprints and spectral analysis. It is shown that local errors in global and basin-scale systems can be significantly reduced when assimilating observations from regional observing systems.

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