International Conference in Shallow-Water Acoustics

The International Conference in Shallow-Water Acoustics (known as SWAC '97) was successfully held in Beijing, China, from April 21 to 25, 1997. There were many participating countries. The conference consisted of invited and contributed papers on important topics of shallow-water acoustics. A major accomplishment is that SWAC '97 and the post-conference tour have led to a strong dialog with the Chinese, Japanese, Korean, Singaporean, Russian and Indian scientists. An international steering group workshop to investigate the scientific, engineering and logistic rationales that might form the basis for a collaborative international experiment in the seas of China is now in the planning.Approved for public release; distribution unlimite

Estimation of planetary wave parameters from the data of the 1981 ocean acoustic tomography experiment

Submitted in partial fulfillment of the requirements for the degree of Doctor of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1985Using the maximum-likelihood estimation method and minimization techniques, quasi-geostrophic wave solutions were fitted to the observations of the 1981 Ocean Acoustic Tomography Experiment. The experiment occupied a 300 km square area centered at 26°N, 70°W, and had a duration of ~80 days. The data set consisted of acoustic travel-time records, temperature records and CTD profiles, obtained from the acoustic tomographic array, moored temperature sensors and recorders, and ship surveys, respectively. While the latter two were conventional spot measurements, the former corresponds to integral measurements of the temperature (or sound-speed) field. The optimal fit to the data corresponded to 3 waves in the first baroclinic mode, evolving under the presence of a westward mean flow with vertical shear. The flow was estimated to be weak (~2 cm/s), but it changed the wave periods significantly by producing large Doppler shifts. The waves were dynamically stable to the mean flow, had weak nonlinear interactions with each other and did not form a resonant traid; thus they constituted a fully linear solution. Evidence for the existence of the waves was strongly supported by the high correlation (~0.9) between the data and the fit, the large amount of signal energy resolved (~80 percent), the excellent quality of the wave-parameter estimate (only about 10 percent in error), and the general agreement between the observations and quasi-geostrophic linear dynamics.My financial support for the first two years came from the Education Office at W.H.O.I. My dissertation research was supported by ONR Grant NOOOl4-82-C0019

Coupled Ocean Acoustics And Physical Oceanography Observations: In The South China Sea: The NPS Acoustic Component

LONG TERM GOALS: To study the dynamic processes of tropical cyclone (TC) development in the western North Pacific through field observational data and theoretical modeling.N00014-03-WR-2000

32-Channel Digitizer for a Moored Hydrophone

Long Term Goals: Acquisition of an in situ, 32-chanel digitizer capable of sampling at a rate of 8kHz, with a maximum depth rating of 1 km and data storage capacity sufficient to support continuous recording for a 10-day deployment. This system, when coupled to an existing, 32-channel hydrophone array owned by the Naval Postgraduate School, will enable future research efforts to investigate three-dimentional effects on sound propagation caused by a sharp front, large amplitude internal waves, and significant batheymetri changes, which are common environmental features in a shelf-slope environment. The procurement of the proposed 32-channel digitizer will help to fill the data and knowledge gaps that exist in the shallow-water acoustics research community. The first deployment will be in the next multi-institutional shallow-water acoustics experiment that is targeted for the FY14 timeframe

A report on the 3-D acoustic working group meeting at Long Beach, MS July 7-8, 1988

At the request of ONR Code 11250A, the Woods Hole Oceanographic Institution (Dr. James F. Lynch) convened a workshop to bring together a group of acoustic and ocean modelers to review and discuss 1. the state of development and the need for three-dimensional numerical acoustic research propagation and scattering models; 2. the interfacing of acoustic models with available oceanographic data and ocean model outputs. The workshop was hosted by the Institute for Naval Oceanography (Dr. Ching-Sang Chiu) at Long Beach, MS on July 7-8, 1988. This report summarizes the research presentations and the recommendations made by the group. The workshop was an initial attempt to promote the interaction between the ocean and acoustic modeling communities. This interaction between the communities is essential to the development of truly interactive basic research acoustic and ocean models. We anticipate more workshops of such nature to be held in the future. The findings and recommendations generated by these workshops are expected to have a strong impact on the direction of future three-dimensional modeling research in both acoustics and oceanography .Funding was provided by the Office of Naval Research under contract Number N00014-88-K-0363

Towards the Use of POP in a Global Coupled Navy Prediction System

LONG-TERM GOALS: Development of a global high resolution coupled atmosphere/ocean/ice model that assimilates data providing initial conditions from which forecasts are performed. Additionally, very high-resolution regional air/ocean coupled models will be nested into the global system at key strategic locations.Award Number: N0001401WR2015

Enhanced acoustic mode coupling resulting from an internal solitary wave approaching the shelfbreak in the South China Sea

Author Posting. © Acoustical Society of America, 2013. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 133 (2013): 1306-1319, doi:10.1121/1.4789358.Internal waves and bathymetric variation create time- and space-dependent alterations in the ocean acoustic waveguide, and cause subsequent coupling of acoustic energy between propagating normal modes. In this paper, the criterion for adiabatic invariance is extended to the case of an internal solitary wave (ISW) encountering a sloping bathymetry (i.e., continental shelfbreak). Predictions based on the extended criterion for adiabatic invariance are compared to experimental observations from the Asian Seas International Acoustics Experiment. Using a mode 1 starter field, results demonstrate time-dependent coupling of mode 1 energy to higher adjacent modes, followed by abrupt coupling of mode 5–7 energy to nonadjacent modes 8–20, produces enhanced mode coupling and higher received levels downrange of the oceanographic and bathymetric features. Numerical simulations demonstrate that increasing ISW amplitude and seafloor slope enhance the coupling of energy to adjacent and nonadjacent modes. This enhanced coupling is the direct result of the simultaneous influence of the ISW and its proximity to the shelfbreak, and, compared to the individual effect of the ISW or shelfbreak, has the capacity to scatter 2–4 times the amount of acoustic energy from below the thermocline into the upper water column beyond the shelfbreak in realistic environments.The ASIAEX and NLIWI experiments were supported jointly by the National Science Council of Taiwan and the U.S. Office of Naval Research

Array data acquisition with wireless LAN telemetry as applied to shallow water tomography in the Barents Sea

This report describes the application of a new technique of digital radio telemetry, based on a recently available wireless Local Area Network Ethernet adapter, to the need for realtime transmission of data from a vertical line array (VLA) of hydrophones to a nearby ship. The report is technical in nature and discusses the design and performance of the system as used during the Barents Sea Polar Front Experiment in August 1992. A key feature of the use of LAN technology in a "telemetry" application is the availability of Transmission Control Protocol (TCP) software for Ethernet hardware that greatly eases the task of achieving error free digital data over a radio link prone to dropouts.Funding was provided by the Long Beach Naval Regional Contracting Center Detachment under Contract N00123-92-C-007l and the Office of Naval Research under Contract N000l4-9l-J-1246

Introduction to the special issue on three-dimensional underwater acoustics

Author Posting. © Acoustical Society of America, 2019. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 146(3), (2019): 1855-1857, doi:10.1121/1.5126013.This special issue focuses on compelling three-dimensional (3D) volumetric and boundary effects on underwater sound propagation and scattering in complex and time-varying (thus four-dimensional) underwater environments. It consists of 24 papers covering analytical, numerical, and experimental studies and presents a collection of up-to-date research on this active and relevant topic.2020-03-3

South China Sea internal tide/internal waves-impact on the temporal variability of horizontal array gain at 276 Hz

Author Posting. © IEEE, 2004. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 29 (2004): 1292-1307, doi:10.1109/JOE.2004.836794.The temporal variability of the spatial coherence of an acoustic signal received on a bottomed horizontal array has been calculated for 276-Hz narrow-band signals. A conventional plane wave beamformer was applied to the received signals. The temporal variability of the array's omnipower, beam power, and array gain are related to variability in the sound-speed field. The spectral characteristics of array omnipower are nonstationary and changed as the spectral characteristics of the temperature field varied. The array omnipower and beam-power variability tracked each other in time and varied by as much as 15 dB over time intervals as short as 7 min. Array gain varied up to 5 dB and usually tracked the omnipower variability. A contiguous 24-h section of data is discussed in detail. This data section is from a time period during which the high-frequency fluid dynamic perturbation of the sound-speed field was of smaller amplitude than other sections of the 16-d data set. Consequently, this section of data sets an upper bound for the realizable array gain. The temporal variability of array gain and spatial coherence at times appears to be correlated with environmental perturbation of the sound-speed field, but are also correlated with changes in the signal-to-noise ratio. The data was acquired during the Office of Naval Research's South China Sea Asian Seas International Acoustics Experiment. The 465-m 32-channel horizontal array was placed on the bottom in 120 m of water at the South China Sea shelf break. The acoustic source was moored in 114 m of water /spl sim/19 km from the receiving array.This work was supported by the Office of Naval Research