Underwater Acoustics, Modeling and Simulation
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The subject of underwater acoustic modeling deals with the translation of our physical understanding of sound in the sea into mathematical formulas solvable by computers. This four-day course provides a comprehensive treatment of all types of underwater acoustic models including environmental, propagation, noise, reverberation, and sonar performance models. Specific examples of each type of model are discussed to illustrate model formulations, assumptions, and algorithm efficiency. Guidelines for selecting and using available propagation, noise, and reverberation models are highlighted. Problem sessions allow students to exercise PC-based propagation and active sonar models. Each student will receive a copy of Underwater Acoustic Modeling and Simulation (5th edition)by Paul C. Etter (a $190 value) in addition to a complete set of lecture notes.
What You Will Learn:
- What models are available to support sonar engineering and oceanographic research.
- How to select the most appropriate models based on user requirements.
- Where to obtain the latest models and supporting databases.
- How to operate models, generate reliable results, and assess prediction uncertainties.
- How to solve the active and passive sonar equations to simulate sonar performance.
- How acoustic models serve as enabling tools for assessing noise impacts on the ocean soundscape.
- What regulations govern protection of marine mammals while operating sonar equipment.
- Introduction. Nature of acoustical measurements and prediction. Modern developments in physical and mathematical modeling. Diagnostic versus prognostic applications. Latest developments in acoustic sensing of the oceans.
- Acoustical Oceanography. Distribution of physical and chemical properties in the oceans. Sound-speed calculation, measurement, and distribution. Surface and bottom boundary conditions. Effects of circulation patterns, fronts, eddies and fine-scale features on acoustics. Biological effects. References.
- Propagation. Observations and Physical Models. Basic concepts, boundary interactions, attenuation, and absorption. Shear-wave effects in the sea floor and ice cover. Ducting phenomena including surface ducts, sound channels, convergence zones, shallow-water ducts, and Arctic half-channels. Spatial and temporal coherence. Mathematical Models. Theoretical basis for propagation modeling. Frequency- domain wave equation formulations including ray theory, normal mode, multipath expansion, fast field, and parabolic approximation techniques. Energy-flux models. Prediction uncertainties in complex environments. New developments in shallow-water and under-ice models. Domains of applicability. Model summary tables organized according to domains. Data support requirements. Specific examples (PE and RAYMODE). References. Demonstrations.
- Noise. Observations and Physical Models. Noise sources and spectra. Depth dependence and directionality. Slope-conversion effects. Mathematical Models. Theoretical basis for noise modeling. Ambient noise and beam-noise statistics models. Pathological features arising from inappropriate assumptions. Model summary tables organized according to domains. Data support requirements. Specific example (RANDI-III). References.
- Reverberation. Observations and Physical Models. Volume and boundary scattering. Shallow- water and under-ice reverberation features. Mathematical Models. Theoretical basis for reverberation modeling. Cell scattering and point scattering techniques. Bistatic reverberation formulations and operational restrictions. Model summary tables organized according to domains. Data support requirements. Specific examples (REVMOD and Bistatic Acoustic Model). References.
- Sonar Performance Models. Sonar equations for monostatic, bistatic, and multistatic systems. Advanced signal processing issues in clutter environments. Model operating systems. Model summary tables organized according to domains. Data support requirements. Sources of oceanographic and acoustic data. Specific examples (NISSM and Generic Sonar Model). References. Demonstrations.
- Simulation. Review of simulation theory including advanced methodologies and infrastructure tools. Overview of engineering, engagement, mission, and theater level models. Discussion of applications in concept evaluation, training, and resource allocation. References.
- Effects of Sound on the Marine Environment. Changes in the ocean soundscape driven by anthropogenic activity (e.g. marine hydrokinetic devices) and natural factors (e.g. ocean acidification). Mitigation of marine-mammal endangerment. References.
- Special Applications. Inverse acoustic sensing. Stochastic modeling, broadband modeling, matched field processing, acoustic tomography, coupled ocean-acoustic modeling, 3D modeling, nonlinear acoustics, and chaotic metrics. Rapid environmental assessments. Underwater acoustic networks and vehicles, channel models, and localization methods. Through-the-sensor parameter estimation. Seismic oceanography. References.
- Model Evaluation. Guidelines for model evaluation and documentation. Analytical benchmark solutions. Theoretical and operational limitations. Verification, validation and accreditation. Examples.
- Demonstrations and Problem Sessions. In-class demonstration of PC-based propagation and active sonar models. Hands-on problem sessions and discussion of results.
Paul C. Etter has worked in the fields of ocean-atmosphere physics and environmental acoustics for the past forty years supporting federal and state agencies, academia, and private industry. He received his BS degree in Physics and his MS degree in Oceanography at Texas A&M University. Mr. Etter served on active duty in the U.S. Navy as an Anti-Submarine Warfare (ASW) Officer aboard frigates. He is the author or co-author of more than 200 technical reports, professional papers, and books addressing environmental measurement technology, underwater acoustics, and physical oceanography. Mr. Etter is the author of the textbook Underwater Acoustic Modeling and Simulation (5th edition).
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