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The primary objectives of this project are to: (i) build a suite of ocean models of the Philippine Sea (PS) of varying resolutions and dynamical representations; ii) perform twin experiments to examine how assimilation of full-spectra observations (including scales not resolved by the models) into simplified models impacts predictability; iii) generate covariance data from a suite of models to generate new Kalman gain matrix estimates; iv) use the Kalman estimate with the Green's function assimilation (as opposed to an adjoint) to compare different assimilation efforts; v) examine scaleselective error in the observations; vi) transition the results and methodology to NRL for further examination and possible inclusion into NRL operations.

The Arctic Ocean is currently undergoing dramatic changes, including reductions in the extent and thickness of the ice cover and extensive warming of the intermediate layers (Fig. 1). The multiyear ice is melting. Ice keels are getting smaller. With more open water, the internal wave energy level and therefore acoustic volume scattering are likely increasing, at least during summer. What was learned about acoustic propagation and ambient noise in the Arctic during the Cold War is now obsolete. The long-term objectives of this research program are to understand the effects of changing Arctic conditions on low-frequency, deep-water propagation and on the low-frequency ambient noise field. The goal is to determine the fundamental limits to signal processing in the Arctic imposed by ocean and ice processes. The hope is that these first few new steps will lead to a larger, permanent acoustic monitoring, communications, and navigation network in the Arctic Ocean. This research effort was funded as an expansion of ONR Grant N00014-12-1-0226, entitled North Pacific Acoustic Laboratory: Deep Water Acoustic Propagation in the Philippine Sea. This annual report is in addition to the annual report for ONR Grant N00014-12-1-0226 that describes the research effort in the Philippine Sea.

This work seeks to understand the effects of topography on the ocean general circulation with a focus on the wide range of scales in the interactions. The small-scale details of the topography and the drag and turbulence generated at the boundary (at scales from meters to mesoscale) interact in the boundary layers to influence the larger-scale flow. We will study these issues through ocean model simulations, adjoint sensitivity experiments, and state estimation using measurements in the region surrounding an island in the westward-flowing limb of the subtropical gyre.

The propagation of remotely generated superinertial internal tides constitutes a difficulty for the modelling of regional ocean tidal variability which we illustrate in several ways. First, the M2 tidal solution inside a control region located along the Southern California Bight coastline is monitored while the extent of the numerical domain is increased (up to 512 x 512 km). While the amplitude and phase of sea level averaged over the region is quasi-insensitive to domain size, a steady increase of kinetic energy, predominantly baroclinic, is observed with increasing domain size. The increasing flux of energy into the control region suggests that this trend is explained by the growing contribution from remote generation sites of internal tide which can propagate up to the control region. Increasing viscosities confirms this interpretation by lowering baroclinic energy levels and limiting their rate of increase with domain size. Doubling the grid spacing allows consideration of numerical domains 2 times larger. While the coarse grid has lower energy levels than the finer grid, the rate of energy increase with domain size appears to be slowing for the largest domain of the coarse grid simulations. Forcing the smallest domain with depth-varying tidal boundary conditions from the simulation in the largest domain produces energy levels inside the control region comparable to those in the control region for the largest domain, thereby confirming the feasibility of a nested approach. In contrast, simulations forced with a subinertial tidal constituent (K1) show that when the propagation of internal tide is limited, the control region kinetic energy is mostly barotropic and the magnitudes of variations of the kinetic energy with domain size are reduced. (C) 2012 Elsevier Ltd. All rights reserved.

Author Posting. © The Oceanography Society, 2013. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 26, no. 1 (2013): 66–79, doi:10.5670/oceanog.2013.06., Numerous observational and modeling studies of ocean circulation surrounding Taiwan have reported occurrences of cold water and doming of isotherms (called the cold dome) that result in the formation of coastal upwelling on the northeastern Taiwan shelf. We use a high-resolution (1/24°) ocean model based on the Massachusetts Institute of Technology general circulation model to study the evolution of this distinct shelf-slope circulation phenomenon. We performed a number of model simulations spanning a five-year period (2004–2008) using realistic atmospheric forcing and initial and open boundary conditions. The model solutions were compared with satellite measurements of sea surface height (SSH), sea surface temperature (SST), and historical temperature and salinity observations. The model showed a realistically shaped cold dome with a diameter of ~ 100 km and temperature of ~ 3°C below the ambient shelf waters at 50 m depth. The occurrences of simulated cold dome events appeared to be connected with the seasonal variability of the Kuroshio Current. The model simulations showed more upwelling events during spring and summer when the core of the Kuroshio tends to migrate away from the east coast of Taiwan, compared to fall and winter when the core of the Kuroshio is generally found closer to the east coast of Taiwan. The model also reproduced weak cyclonic circulation associated with the upwelling off northeastern Taiwan. We analyzed the spatio-temporal variability of the cold dome using the model solution as a proxy and designed a "cold dome index" based on the temperature at 50 m depth averaged over a 0.5° × 0.5° box centered at 25.5°N, 122°E. The cold dome index correlates with temperature at 50 m depth in a larger region, suggesting the spatial extent of the cold dome phenomenon. The index had correlation maxima of 0.78 and 0.40 for simulated SSH and SST, respectively, in and around the cold dome box region, and we hypothesize that it is a useful indicator of upwe, This work was supported by Office of Naval Research grant N00014-08- 1-0587.

The network comprising 61 high-frequency radar systems along the U.S. West Coast (USWC) provides a unique, high resolution, and broad scale view of ocean surface circulation. Subinertial alongshore surface currents show poleward propagating signals with phase speeds of O(10) and O(100–300) km d 1 that are consistent with historical in situ observations off the USWC and that can be possibly interpreted as coastally trapped waves (CTWs). The propagating signals in the slow mode are partly observed in southern California, which may result from scattering and reflection of higher-mode CTWs due to curvature of shoreline and bathymetry near Point Conception, California. On the other hand, considering the order of the phase speed in the slow mode, the poleward propagating signals may be attributed to alongshore advection or pressure-driven flows. A statistical regression of coastal winds at National Data Buoy Center buoys on the observed surface currents partitions locally and remotely wind-forced components, isolates footprints of the equatorward propagating storm events in winter off the USWC, and shows the poleward propagating signals year round.

As an aid to understanding long-range acoustic propagation in the Philippine Sea, statistical and phenomenological descriptions of sound-speed variations were developed. Two moorings of oceanographic sensors located in the western Philippine Sea in the spring of 2009 were used to track constant potential-density surfaces (isopycnals) and constant potential-temperature surfaces (isotherms) in the depth range 120–2000 m. The vertical displacements of these surfaces are used to estimate sound-speed fluctuations from internal waves, while temperature/salinity variability along isopycnals are used to estimate sound-speed fluctuations from intrusive structure often termed spice. Frequency spectra and vertical covariance functions are used to describe the space-time scales of the displacements and spiciness. Internal-wave contributions from diurnal and semi-diurnal internal tides and the diffuse internal-wave field [related to the Garrett–Munk (GM) spectrum] are found to dominate the sound-speed variability. Spice fluctuations are weak in comparison. The internal wave and spice frequency spectra have similar form in the upper ocean but are markedly different below 170-m depth. Diffuse internal-wave mode spectra show a form similar to the GM model, while internal-tide mode spectra scale as mode number to the minus two power. Spice decorrelates rapidly with depth, with a typical correlation scale of tens of meters.

An important element of present oceanographic research is the assessment and quantification of uncertainty. These studies are challenging in the coastal ocean due to the wide variety of physical processes occurring on a broad range of spatial and temporal scales. In order to assess new methods for quantifying and predicting uncertainty, a joint Taiwan-US field program was undertaken in August/September 2009 to compare model forecasts of uncertainties in ocean circulation and acoustic propagation, with high-resolution in situ observations. The geographical setting was the continental shelf and slope northeast of Taiwan, where a feature called the "cold dome" frequently forms. Even though it is hypothesized that Kuroshio subsurface intrusions are the water sources for the cold dome, the dome's dynamics are highly uncertain, involving multiple scales and many interacting ocean features. During the experiment, a combination of near-surface and profiling drifters, broad-scale and high-resolution hydrography, mooring arrays, remote sensing, and regional ocean model forecasts of fields and uncertainties were used to assess mean fields and uncertainties in the region. River runoff from Typhoon Morakot, which hit Taiwan August 7–8, 2009, strongly affected shelf stratification. In addition to the river runoff, a cold cyclonic eddy advected into the region north of the Kuroshio, resulting in a cold dome formation event. Uncertainty forecasts were successfully employed to guide the hydrographic sampling plans. Measurements and forecasts also shed light on the evolution of cold dome waters, including the frequency of eddy shedding to the north-northeast, and interactions with the Kuroshio and tides. For the first time in such a complex region, comparisons between uncertainty forecasts and the model skill at measurement locations validated uncertainty forecasts. To complement the real-time model simulations, historical simulations with another model show that large Kuroshio intru

The long-term scientific objective of the Quantifying, Predicting, and Exploiting (QPE) Uncertainty Directed Research Initiative (DRI) is to improve the assessment of uncertainty in observations and predictions of sound propagation in littoral regions. The objectives of this research are to understand and exploit the effects of the ocean state on acoustic propagation and detection. This work will contribute to the goals through global and regional physical ocean modeling and data assimilation. The modeling includes both model comparisons with observations, evaluating model error, and forecast and predictability studies to see the growth of uncertainty in time and space and the influences of the past ocean state on the acoustic propagation conditions on the shelf north of Taiwan. The QPE DRI is a coordinated effort in which many types of measurements have been collected over the continental shelf to the north of Taiwan. The field results will be used to help characterize the rapidly varying physical environment in comparison to the models and to study acoustic propagation and scattering in the region. Two of the most important physical processes in the region of the experiment are the cold dome observed off the northwest corner of Taiwan and intrusions of the Kuroshio onto the shelf north of Taiwan.

The boundary currents off the east coast of the Philippines are of critical importance to the general circulation of the Pacific Ocean. The westward flowing North Equatorial Current (NEC) runs into the Philippine coast and bifurcates into the northward Kuroshio and the southward Mindanao Current (MC). The partitioning of the flow into the Kuroshio and MC is an important observable. Quantifying these flows and understanding bifurcation dynamics are essential to improving predictions of regional circulation, and to characterizing property transports that ultimately affect Pacific climate. Fluctuations in the Kuroshio and MC can significantly impact variability downstream. For example, the Kuroshio penetrates through Luzon Strait into the South China Sea and onto the East China Sea shelf. The Kuroshio front dramatically alters stratification and may impact internal wave climate. This study incorporates observation, theory, and modeling to make fundamental advances in our knowledge of the origins of the Kuroshio and Mindanao current.

Author Posting. © Acoustical Society of America, 2012. 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 131 (2012): 1733-1748, doi:10.1121/1.3666014., Environmental sensors moored on the New Jersey continental shelf tracked constant density surfaces (isopycnals) for 35 days in the summer of 2006. Sound-speed fluctuations from internal-wave vertical isopycnal displacements and from temperature/salinity variability along isopycnals (spiciness) are analyzed using frequency spectra and vertical covariance functions. Three varieties of internal waves are studied: Diffuse broadband internal waves (akin to waves fitting the deep water Garrett/Munk spectrum), internal tides, and, to a lesser extent, nonlinear internal waves. These internal-wave contributions are approximately distinct in the frequency domain. It is found that in the main thermocline spicy thermohaline structure dominates the root mean square sound-speed variability, with smaller contributions coming from (in order) nonlinear internal waves, diffuse internal waves, and internal tides. The frequency spectra of internal-wave displacements and of spiciness have similar form, likely due to the advection of variable-spiciness water masses by horizontal internal-wave currents, although there are technical limitations to the observations at high frequency. In the low-frequency, internal-wave band the internal-wave spectrum follows frequency to the −1.81 power, whereas the spice spectrum shows a −1.73 power. Mode spectra estimated via covariance methods show that the diffuse internal-wave spectrum has a smaller mode bandwidth than Garrett/Munk and that the internal tide has significant energy in modes one through three., This work was supported by the Office of Naval Research, and Professor Colosi gratefully acknowledges his additional support from the Naval Postgraduate School’s Undersea Warfare Chair that he holds.

Author Posting. © The Oceanography Society, 2011. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 24 no. 4 (2011): 110–121, doi:10.5670/oceanog.2011.99., An important element of present oceanographic research is the assessment and quantification of uncertainty. These studies are challenging in the coastal ocean due to the wide variety of physical processes occurring on a broad range of spatial and temporal scales. In order to assess new methods for quantifying and predicting uncertainty, a joint Taiwan-US field program was undertaken in August/September 2009 to compare model forecasts of uncertainties in ocean circulation and acoustic propagation, with high-resolution in situ observations. The geographical setting was the continental shelf and slope northeast of Taiwan, where a feature called the "cold dome" frequently forms. Even though it is hypothesized that Kuroshio subsurface intrusions are the water sources for the cold dome, the dome's dynamics are highly uncertain, involving multiple scales and many interacting ocean features. During the experiment, a combination of near-surface and profiling drifters, broad-scale and high-resolution hydrography, mooring arrays, remote sensing, and regional ocean model forecasts of fields and uncertainties were used to assess mean fields and uncertainties in the region. River runoff from Typhoon Morakot, which hit Taiwan August 7–8, 2009, strongly affected shelf stratification. In addition to the river runoff, a cold cyclonic eddy advected into the region north of the Kuroshio, resulting in a cold dome formation event. Uncertainty forecasts were successfully employed to guide the hydrographic sampling plans. Measurements and forecasts also shed light on the evolution of cold dome waters, including the frequency of eddy shedding to the north-northeast, and interactions with the Kuroshio and tides. For the first time in such a complex region, comparisons between uncertainty forecasts and the model skill at measurement locations validated uncertainty forecasts. To complement the real-time model simulations, historical simulations with another model show that large Kuroshio intru, We thank the National Science Council of Taiwan as well as the Office of Naval Research for generous support of this effort.

An important element of present oceanographic research is the assessment and quantification of uncertainty. These studies are challenging in the coastal ocean due to the wide variety of physical processes occurring on a broad range of spatial and temporal scales. In order to assess new methods for quantifying and predicting uncertainty, a joint Taiwan-US field program was undertaken in August/September 2009 to compare model forecasts of uncertainties in ocean circulation and acoustic propagation, with high-resolution in situ observations. The geographical setting was the continental shelf and slope northeast of Taiwan, where a feature called the "cold dome" frequently forms. Even though it is hypothesized that Kuroshio subsurface intrusions are the water sources for the cold dome, the dome's dynamics are highly uncertain, involving multiple scales and many interacting ocean features. During the experiment, a combination of near-surface and profiling drifters, broad-scale and high-resolution hydrography, mooring arrays, remote sensing, and regional ocean model forecasts of fields and uncertainties were used to assess mean fields and uncertainties in the region. River runoff from Typhoon Morakot, which hit Taiwan August 7–8, 2009, strongly affected shelf stratification. In addition to the river runoff, a cold cyclonic eddy advected into the region north of the Kuroshio, resulting in a cold dome formation event. Uncertainty forecasts were successfully employed to guide the hydrographic sampling plans. Measurements and forecasts also shed light on the evolution of cold dome waters, including the frequency of eddy shedding to the north-northeast, and interactions with the Kuroshio and tides. For the first time in such a complex region, comparisons between uncertainty forecasts and the model skill at measurement locations validated uncertainty forecasts. To complement the real-time model simulations, historical simulations with another model show that large Kuroshio intru, National Science Council of Taiwan, United States. Office of Naval Research

LONG-TERM GOALS: Our long-term goal is to study the sensitivity behavior of travel-time and arrival-amplitude observables due to sound-speed perturbations in low-frequency, long-range acoustic propagation in the ocean. OBJECTIVES: The leading objective of this project is to rigorously study the asymptotic behavior of wave-theoretic travel-time sensitivity kernels with increasing range, as a means to explain their observed convergence towards the corresponding ray-theoretic sensitivity kernels even at low frequencies. Further objectives include the derivation and study of 2D and 3D first-order amplitude sensitivity kernels, as well as vertical sensitivity kernels for arrival amplitudes, first- and second-order. A last objective is the study of sensitivity behavior of late arrivals depending on propagation frequency and range. APPROACH: Previous work has revealed a numerical convergence of wave-theoretic travel-time vertical sensitivity kernels (VTSKs) towards the corresponding ray-theoretic sensitivity kernels with increasing range even at low frequencies [1]. To study this behavior, the asymptotic form of finite-frequency kernels with increasing range is rigorously derived here using a stationary-phase approach [2]. The wave-theoretic VTSK involves an integral over frequency with a rapidly oscillating kernel, the oscillation rate increasing with propagation range. The stationary-phase approach is used to evaluate the asymptotic form of this integral and finally of the VTSK for long ranges.

The boundary currents off the east coast of the Philippines are of critical importance to the general circulation of the Pacific Ocean. The westward flowing North Equatorial Current (NEC) runs into the Philippine coast and bifurcates into the northward Kuroshio and the southward Mindanao Current (MC). The partitioning of the flow into the Kuroshio and MC is an important observable. Quantifying these flows and understanding bifurcation dynamics are essential to improving predictions of regional circulation, and to characterizing property transports that ultimately affect Pacific climate. Fluctuations in the Kuroshio and MC can significantly impact variability downstream. For example, the Kuroshio penetrates through Luzon Strait into the South China Sea and onto the East China Sea shelf. The Kuroshio front dramatically alters stratification and may impact internal wave climate. This study incorporates observation, theory, and modeling to make fundamental advances in our knowledge of the origins of the Kuroshio and Mindanao currents. The objectives of this project include quantifying flows and water properties, improving understanding of the dynamics of a bifurcation region, and establishing predictability of the three major currents in the region. The observational approach will have two major thrusts: (1) quantifying the fluxes of mass, heat, and salt in the NEC, Kuroshio, and MC; and (2) establishing Lagrangian patterns of flow. To quantify the seasonal cycle and to obtain an initial measure of interannual variability, these observations will be sustained over a three-year period. The bifurcation region is an interesting target, but the stagnation point of a turbulent flow is not an easy quantity to observe. The sustained observations will provide a test for models of the regions, and at the same time will be available for assimilation in models.

The long-term scientific objective of the Quantifying, Predicting, and Exploiting (QPE) Uncertainty Directed Research Initiative (DRI) is to improve the assessment of uncertainty in observations and predictions of sound propagation in littoral regions. The objectives of this research are to understand and exploit the effects of the ocean state on acoustic propagation and detection. This work will contribute to the goals through global and regional physical ocean modeling and data assimilation. The modeling includes both model comparisons with observations, evaluating model error, and forecast and predictability studies to see the growth of uncertainty in time and space and the influences of the past ocean state on the acoustic propagation conditions on the shelf north of Taiwan.

New nonlinear filtering algorithms were developed and are currently being tested. Numerical results suggest that nonlinear filters behave better than the ensemble Kalman filter methods with strongly nonlinear systems. They also seem to respect the dynamical of the system state more resulting in more stable predictions.

The boundary currents off the east coast of the Philippines are of critical importance to the general circulation of the Pacific Ocean. The westward flowing North Equatorial Current (NEC) runs into the Philippine coast and bifurcates into the northward Kuroshio and the southward Mindanao Current (MC). The partitioning of the flow into the Kuroshio and MC is an important observable. Quantifying these flows and understanding bifurcation dynamics are essential to improving predictions of regional circulation, and to characterizing property transports that ultimately affect Pacific climate. Fluctuations in the Kuroshio and MC can significantly impact variability downstream. For example, the Kuroshio penetrates through Luzon Strait into the South China Sea and onto the East China Sea shelf. The Kuroshio front dramatically alters stratification and may impact internal wave climate. This study incorporates observation, theory, and modeling to make fundamental advances in our knowledge of the origins of the Kuroshio and Mindanao current.

The long-term scientific objective of the Quantifying, Predicting, and Exploiting (QPE) Uncertainty Directed Research Initiative (DRI) is to improve the assessment of uncertainty in observations and predictions of sound propagation in littoral regions. The objectives of this research are to understand and exploit the effects of the ocean state on acoustic propagation and detection. This work will contribute to the goals through global and regional physical ocean modeling and data assimilation. The modeling includes both model comparisons with observations, evaluating model error, and forecast and predictability studies to see the growth of uncertainty in time and space and the influences of the past ocean state on the acoustic propagation conditions on the shelf north of Taiwan.

The North Pacific Acoustic Laboratory (NPAL) program is intended to improve our understanding of (i) the basic physics of low-frequency, broadband propagation in deep water, including the effects of oceanographic variability on signal stability and coherence, (ii) the structure of the ambient noise field in deep water at low frequencies, and (iii) the extent to which acoustic methods, together with other measurements and coupled with ocean modeling, can yield estimates of the time-evolving ocean state useful for acoustic predictions. The goal is to determine the fundamental limits to signal processing in deep water imposed by ocean processes, enabling advanced signal processing techniques to capitalize on the three-dimensional character of the sound and noise fields.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1983., Microfiche copy available in Archives and Science, Bibliography: leaves 355-359., by Bruce Douglas Cornuelle., Ph.D.

The North Pacific Acoustic Laboratory (NPAL) program is intended to improve our understanding of (i) the basic physics of low-frequency, broadband propagation in deep water, including the effects of oceanographic variability on signal stability and coherence, (ii) the structure of the ambient noise field in deep water at low frequencies, and (iii) the extent to which acoustic methods, together with other measurements and coupled with ocean modeling, can yield estimates of the time-evolving ocean state useful for acoustic predictions. The goal is to determine the fundamental limits to signal processing in deep water imposed by ocean processes, enabling advanced signal processing techniques to capitalize on the three-dimensional character of the sound and noise fields., Code 1 only. The original document contains color images.

The long-term scientific objective of the Quantifying, Predicting, and Exploiting (QPE) Uncertainty Directed Research Initiative (DRI) is to improve the assessment of uncertainty in observations and predictions of sound propagation in littoral regions.

The long-term scientific objective is to develop a fully nonlinear Bayesian approach that generalizes the optimality of ensemble Kalman filter methods to nonlinear systems and can be suitable for large dimensional data assimilation problems. The approach will be tested with realistic applications to ocean data assimilation problems. The goal of this research is to explore a new direction that can lead to fully nonlinear filters that can perform better than the ensemble Kalman filter (EnKF) methods with highly nonlinear systems at reasonable computational requirements. We aim at proposing, implementing and testing new nonlinear Kalman filters with ocean data assimilation problems in mind. Simple nonlinear dynamical models will be first considered to evaluate the behavior of these new filters and assess their efficiency compared to the EnKF methods.

The long-term scientific objective of the Quantifying, Predicting, and Exploiting (QPE) Uncertainty Directed Research Initiative (DRI) is to improve the assessment of uncertainty in observations and predictions of sound propagation in littoral regions.

Our long-term goal is to develop reliable tools for modeling the sensitivity of travel-time observables to sound-speed perturbations in low-frequency long-range acoustic propagation in the ocean and associated tomography experiments., Prepared in cooperation with Scripps Institution of Oceanography, Univeristy of California, San Diego, La Jolla, CA. The original document contains color images.

The North Pacific Acoustic Laboratory (NPAL) program is intended to improve our understanding of (i) the basic physics of low-frequency, broadband propagation in deep water, including the effects of oceanographic variability on signal stability and coherence, (ii) the structure of the ambient noise field in deep water at low frequencies, and (iii) the extent to which acoustic methods, together with other measurements and coupled with ocean modeling, can yield estimates of the time-evolving ocean state useful for acoustic predictions. The goal is to determine the fundamental limits to signal processing in deep water imposed by ocean processes, enabling advanced signal processing techniques to capitalize on the three-dimensional character of the sound and noise fields., code 1 only. The original document contains color images.

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution April 1983, Ocean acoustic tomography was proposed in 1978 by Munk and Wunsch as a possible technique for monitoring the evolution of temperature, density, and current fields over large regions. In 1981, the Ocean Tomography Group deployed four 224 Hz acoustic sources and five receivers in an array which fit within a box 300 km. on a side centered on 26°N, 70°W (southwest of Bermuda). The experiment was intended both to demonstrate the practicality of tomography as an observation tool and to extend the understanding of mesoscale evolution in the low-energy region far from the strong Gulf Stream recirculation. The propagation of 224 Hz sound energy in the ocean can be described as a set of rays traveling from source to receiver, with each ray taking a different path through the ocean in a vertical plane connecting the source and receiver. The sources transmitted a phase-coded signal which was processed at the receiver to produce a pulse at the time of arrival of the signal. Rays can be distinguished by their different pulse travel times, and these travel times change in response to variations in sound speed and current in the ocean through which the rays passed. In order to reconstruct the ocean variations from the observed travel time changes, it is necessary to specify models for both the variations and their effect on the travel times. The dependence of travel time on the oceanic sound speed and current fields can be calculated using ray paths traced by computer. The vertical structure of the sound speed and current fields in the ocean were modelled as a combination of Empirical Orthogonal Functions (EOFs) from MODE. The horizontal structure was continuous, but was constrained to have a gaussian covariance with a 100 km. e- folding scale. The resulting estimator closely resembles objective mapping as used in meteorology and physical oceanography. The tomographic system has at present only been used to estimate sound speed structure for comparison with the traditional measurem, My support for the first 3 years came from an NSF graduate fellowship, and I was then supported as a research assistant by NSF Grant OCE-8017791.

Author Posting. © Acoustical Society of America, 1995. 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 98 (1995): 2270-2279, doi:10.1121/1.413341., Numerically simulated acoustic transmission from a single source of known position (for example, suspended from a ship) to receivers of partially known position (for example, sonobuoys dropped from the air) are used for tomographic mapping of ocean sound speed. The maps are evaluated for accuracy and utility. Grids of 16 receivers are employed, with sizes of 150, 300, and 700 km square. Ordinary statistical measures are used to evaluate the pattern similarity and thus the mapping capability of the system. For an array of 300 km square, quantitative error in the maps grows with receiver position uncertainty. The large and small arrays show lesser mapping capability than the mid-size array. Mapping errors increase with receiver position uncertainty for uncertainties less than 1000-m rms, but uncertainties exceeding that have less systematic effect on the maps. Maps of rms error of the field do not provide a complete view of the utility of the acoustic network. Features of maps are surprisingly reproducible for different navigation error levels, and give comparable information about mesoscale structures despite great variations in those levels., This work was supported by Office of Naval Research grants N00014-9l-J-1138 (Arctic Sciences )and N00014-92-I-1162 (Ocean Acoustics).

LONG-TERM GOALS. The goal of this research is to understand and exploit the effects of the ocean state on acoustic propagation and detection. This work will contribute to that goal through regional ocean modeling and data assimilation. The modeling will include forecast and predictability studies to see the growth of uncertainty in time and space and the predictability of the propagation conditions on the shelf north of Taiwan from the ocean state. OBJECTIVES. The objectives and immediate scientific goals of the 1-year project were to contribute to planning the 4-year DRI effort and the experiment north of Taiwan. APPROACH. The experiment will be a coordinated effort in which many types of measurements will be made during the DRI demonstration experiment in FY09 both to help characterize the rapidly varying environment in the northern Philippine Sea and to study acoustic propagation and scattering in the region. The acoustic remote sensing data, together with data from direct measurements and satellite remote sensing, will be assimilated into a regional ocean model to estimate the evolving ocean state. The technical approach will center on using the Frechet derivatives of ocean models to apply gradient-based assimilation of multiple data types, including direct measurements, satellite remote sensing, and deep-water acoustic measurements. Once the regional model and data assimilation machinery is working, Observing System Simulation Experiments (OSSE) will be conducted prior to the FY09 experiment to aid in the design of the experiment and to understand the sensitivity of the models to the various data types and geometries. The intent is to be ready to combine the data obtained during the FY09 experiment with realistic ocean models as soon as the data become available in order to provide accurate estimates of the ocean state.

Our primary objective is to use the wave-theoretic travel-time sensitivity kernel in order to study the effect of increasing range on the sensitivity of finite-frequency travel-time observables to sound-speed perturbations. A further objective is to compare wave-theoretic travel-time sensitivity kernels and Fresnel volumes associated with particular eigenrays, seeking connections between the ray-theoretic and wave-theoretic description of travel-time observables., code 1 only. The original document contains color images.

The North Pacific Acoustic Laboratory (NPAL) program is intended to improve our understanding of: (1) the basic physics of low-frequency, broadband propagation in deep water, including the effects of oceanographic variability on signal stability and coherence, (2) the structure of the ambient noise field in deep water at low frequencies, and (3) the extent to which acoustic methods, together with other measurements and coupled with ocean modeling, can yield estimates of the time-evolving ocean state useful for acoustic predictions. The goal is to determine the fundamental limits to signal processing in deep water imposed by ocean processes, enabling advanced signal processing techniques to capitalize on the three-dimensional character of the sound and noise fields., code 1 only. The original document contains color images.