No abstract
This document describes the MOOS-IvP autonomy software for unmanned marine vehicles and its use in largescale ocean sensing systems. MOOS-IvP is composed of two open-source software projects funded by the Office of Naval Research. MOOS provides a core autonomy middleware capability, and the MOOS project additionally provides a set of ubiquitous infrastructure utilities. The IvP Helm is the primary component of an additional set of capabilities implemented to form a full marine autonomy suite known as MOOS-IvP. This software and architecture are platform and mission agnostic and allow for a scalable nesting of unmanned vehicle nodes to form large-scale, long-endurance ocean sensing systems composed of heterogeneous platform types with varying degrees of communications connectivity, bandwidth, and latency. Published
High-resolution methods based on simulated annealing and full-wave sound propagation models are developed for nonlinear inversion for ocean-bottom properties. Simulated annealing is used to search the high-dimensional parameter space of ocean bottoms for the parameter set corresponding to the best replica field. The parabolic equation method is used to solve range-dependent inversion problems. For data taken by Lynch et al. from a range-dependent region of the Gulf of Mexico [J. Acoust. Soc. Am. 89, 648–665 (1991)], this approach achieves excellent agreement between the theoretical and measured acoustic pressures. The recovered sediment parameters suggest that a sound-speed boundary layer exists in the upper part of the sediment and that the depth of an interface in the sediment is range dependent. For locally range-independent problems, inversion is performed in wave-number space. Large efficiency gains are possible with this approach because the number of wave-number samples required for inversion is much smaller than the number of wave-number samples required for computing replica fields.
A numerically efficient global matrix approach t o the solution of the wave equation in horizontally stratified environments is presented. The field in each layer is expressed as a superposition of the field produced by the sources within the layer and an unknown field satisfying the homogeneous wave equations, both expressed as integral representations in the horizontal wavenumber. The boundary conditions t o be satisfied at each interface then yield a linear system of equations in the unknown wavefield amplitudes, t o be satisfied a t each horizontal wavenumber. As an alternative t o the traditional propagator matrix approaches, the solution technique presented here yields both improved efficiency and versatility. Its global nature makes it well suited t o problems involving many receivers in range as well as depth and to calculations of both stresses and particle velocities. The global solution technique is developed in close analogy to the finite element method, thereby reducing the number of arithmetic operations t o a minimum and making the resulting computer code very efficient in terms of computation time. These features are illustrated by a number of numerical examples from both crustal and exploration seismology.
A unified, self-consistent perturbation approach to rough surface scattering in stratified media is presented. By introducing a boundary-condition operator formulation, the effect of the scattering on the mean field is accounted for by replacing the boundary conditions for the smooth interface with a set of effective boundary conditions involving relatively simple matrix operations. The formulation is valid for any type of interface between fluid or elastic layers, with the only change involved being the actual boundary operators. The use of boundary operator makes the formulation compatible with existing propagation models for stratified media, allowing simulation of scattering loss of the coherent component of the field due to the generation of a scattered field in the stratified fluid-solid media with an arbitrary number of rough interfaces. The scattered field, a by-product of the simulation is, in effect, the reverberation field in the stratified waveguide. The approach is verified by agreement with published theoretical results for specific interface types. Further, it is demonstrated qualitatively how rough surface scattering can account for some of the experimentally observed attenuation of seismic interface waves. Finally, the present approach is shown to agree with experimental results for an Arctic environment with a rough ice cover.
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