IEEE Journal of Oceanic Engineering

Published by Institute of Electrical and Electronics Engineers
Online ISSN: 0364-9059
Publications
Article
The author has developed a new thermometer with a time constant of about 0.5 ms as a part of his two-phase alternating current bridge. The thermometer permits the application of a Pt-wire with a low resistance of about 10-50 m Omega . A resolution of less than 0.001 K in the range of 40deg C can be reached. Properties, experiments, and results from measurements with this fast thermometer are described.
 
Article
There is considerable interest within the underwater acoustics community as to whether a fluid model or a poroelastic (Biot) model provides a more accurate representation of sandy sediments. One key metric used to determine this is the acoustic wave speed in the seabed, since the Biot model predicts a sound speed that is frequency dependent whereas the traditional fluid model assumes a sound speed that is constant with frequency. Results obtained during the 1999 Sediment Acoustics Experiment (SAX99) showed some evidence of sound-speed dispersion [IEEE J. Ocean. Eng., vol. 27, no. 3, pp. 413-428, 2002]. The results were consistent with Biot model predictions that employed inputs based on geophysical measurements made at the site. However, only a limited data set was obtained at frequencies from 1 to 10 kHz where the model exhibited its greatest sound-speed variation. Furthermore, these were relative-rather than absolute-measurements of sound-speed dispersion. During the SAX04 sea trial, conducted in autumn 2004 about a kilometer from the location of the SAX99 site, acoustic data were collected on receivers buried in the seabed using a pair of transmitters located within the seabed and a third located in the water column directly above the buried receivers. This source geometry enabled direct time-of-flight (TOF) measurements of acoustic wave speed along all three Cartesian axes. The results are normalized by the acoustic wave speed in the overlying water. Horizontal measurements yielded absolute dispersion estimates but the vertical data were limited to relative estimates due to uncertainty in the depths of the receivers. Results show dispersion within the error limits of the measurement with normalized sediment sound speed increasing from 1.05 at 600 Hz to 1.13 at 20 kHz. The frequency dependence of the measured sound-speed ratios reported on in this paper is in agreement with a simplified poroelastic model [J. Acoust. Soc. Amer., vol. 110, no. 5, pp. 2276-2281, 200- - 1] evaluated using physical parameters measured nearby during SAX99, but the measured sound-speed ratios are about 3% lower than the model predicts; however, some of the vibracores taken at the SAX04 site indicate the presence of small mud inclusions at about 1-m depth, and model results using the oases seismoacoustic model indicate that the lower sound speeds are consistent with the presence of a thin muddy layer. In addition, sound speed along the vertical axis showed substantially greater variability with frequency than did the measurements along the horizontal axes. Results obtained from a simple numerical model indicate that the greater variability in the vertical direction can be explained by interference from reflected arrivals from a low-speed reflector at approximately 1-m depth. Using the porosity β as a free parameter, a best fit of the poroelastic model to the data is obtained for β = 0.425 . Although this is higher than the value of β = 0.385 measured in the sandy sediment during SAX99, heuristic arguments based on the self-consistent model results and the vibracores are presented to support the hypothesis that localized muddy inclusions at the experimental site increased the average porosity over the horizontal propagation paths and resulted in the lower sound-speed ratios.
 
Article
The initial response pattern for a conventional two-electrode, membrane-type dissolved-oxygen probe connected to an ENDECO model 1125 dissolved-oxygen sensor controller is presented. The controller implements a chronoamperometric technique and involves application of the polarizing potential as a pulse. The pulse duration confines the diffusion boundary within the internal electrolyte and the membrane. The time required for readout stabilization is attributed to the establishment of an equilibrium involving diffusion of reactant and product of the electrochemical reaction. A procedure for minimizing the role of membrane stretch in establishing the equilibrium time is discussed. Data obtained on changing the pulse repetition interval are presented in support of the establishment of an equilibrium condition. Sensor response over a 32-day period is noted. Calibration curve data demonstrate the linearity of response with varying oxygen concentrations. Response time data indicate attainment of better than 99% of full deflection within three minutes of a change in oxygen concentration
 
Article
About 10 years ago, the advanced application flight experiment radiometer scatterometer (AAFE RADSCAT) made its first successful measurements of ocean radar scattering cross section from a NASA C-130 aircraft. This instrument was developed as a research tool to evaluate the use of microwave frequency remote sensors (particularly radars) to provide wind-speed information at the ocean's surface. The AAFE RADSCAT flight missions and analyses helped establish the feasibility of the satellite scatterometer for measuring both wind speed and direction. Probably the most important function of the AAFE RADSCAT was to provide a data base of ocean normalized radar cross-section (NRCS) measurements as a function of the surface wind vector at 13.9 GHz. NRCS measurements over a wide parametric range of incidence angles, azimuth angles, and winds were obtained in a series of RADSCAT aircraft missions from 1973 to 1977. Presented herein are analyses of data from the 26 RADSCAT flights during which the quality of the sensor and the surface wind measurements were felt to be understood. Subsets of this data base were used to model the relationship between the Ku -band radar signature and the ocean-surface wind vector. The models developed partly from portions of this data base, supplemented with data from the Seasat (JASIN Report), were used for inversion of the Seasat-A Satellite Scatterometer (SASS) radar measurements to vector winds. This paper summarizes results from a comprehensive analysis of the RADSCAT/ocean wind signature deduced from this complete data set.
 
Article
Two weeks before Hurricane Ivan reworked the shores and nearshore seafloor of the northeastern Gulf of Mexico, swath bathymetry surveys were conducted with high-frequency (300 and 455 kHz) multibeam echosounders in three areas offshore Santa Rosa Island, FL, an 80-km barrier island extending west from Destin to Pensacola Bay, FL. These surveys were repeated in late October 2004, six weeks after the passage of the hurricane, allowing for quantitative pre- and posthurricane seabed comparisons. Bathymetric difference maps (0.2-0.3-m grid cells) show that sediment accretion exceeded 1 m in areas near the 6-7-m isobaths, where a submerged longshore bar was formed below the breaker zone of large storm waves. Accretion of sediment continued seaward tapering off near the 11-12-m isobaths, with evidence of slight seabed erosion (0.1-0.2 m) seaward of this boundary. Between the 6- and 12-m contour lines, the increase in sediment volume is about 279 000 m <sup>3</sup>/km <sup>2</sup>. Grab samples obtained in the area by Vaughan [IEEE J. Ocean. Eng., vol. 34, no. 4, pp. 495-515, 2009] support the hypothesis that the added material is fine sand eroded from the beach and dunes on Santa Rosa Island by the overwash and inundation associated with Ivan's storm surge and eventually deposited offshore by storm-surge ebb currents. Two-dimensional bottom roughness power density spectra computed from colocated east-west (EW) bathymetry swaths near the 12-m isobath show a post-Ivan threefold increase in root mean square (rms) roughness over the [0.104, 0.495] m<sup>-1</sup> spatial wave number band. Bottom roughness spectrograms computed along individual north-south (NS) survey track lines perpendicular to the shoreline and extending 10 km offshore indicate that Ivan-induced waves and currents reworked the seabed to water depths of at least 22 m, with a twofold to fourfold increase in rms roughness over the [0.023, 0.156] m<sup>-1</sup> spatial wave number band.
 
Article
The problem of associating data with targets in a cluttered multi-target environment is discussed and applied to passive sonar tracking. The probabilistic data association (PDA) method, which is based on computing the posterior probability of each candidate measurement found in a validation gate, assumes that only one real target is present and all other measurements are Poisson-distributed clutter. In this paper, a new theoretical result is presented: the joint probabilistic data association (JPDA) algorithm, in which joint posterior association probabilities are computed for multiple targets (or multiple discrete interfering sources) in Poisson clutter. The algorithm is applied to a passive sonar tracking problem with multiple sensors and targets, in which a target is not fully observable from a single sensor. Targets are modeled with four geographic states, two or more acoustic states, and realistic (i.e., low) probabilities of detection at each sample time. A simulation result is presented for two heavily interfering targets illustrating the dramatic tracking improvements obtained by estimating the targets' states using joint association probabilities.
 
Article
A communications experiment was conducted to investigate the effects of oceanographic fluctuations on high-frequency acoustic transmissions. Source transmissions containing broadband channel probes and phase-shift-keyed (PSK) communication sequences were carried out in 100-m water depth using a stationary 18-kHz source and a stationary 64-hydrophone receive array. Thermistor string data indicate the presence of high-frequency temperature fluctuations generated by the internal tide as it progress along the continental shelf. Results show that, because of a downward refracting profile, ray paths are most dense near the bottom, which maximizes wavefront interaction with the fluctuating temperature field.
 
Article
The absolute electrical conductivity at 15deg C of several lots of standard seawater has been measured with great precision as a function of chlorinity. Potassium chloride (KCI) solutions of known concentration and having almost the same conductivity were also measured and the concentration giving the same conductivity at 15deg C as 35.0000permil standard seawater (Chl = 19.37394permil ) was found to be 32.4352 g/kg.
 
Article
Towed-array research and development over 86 years is examined from the inventions of Dr. H. C. Hayes during World War I to multiple arrays towed by oil exploration ships in 2003. Time lines of the effort over the years are presented for array applications to military surface ships, submarines, and for oil exploration efforts. Military surface ship towed-array systems from the Hayes electric eel effort to the SQR-14, SURTASS, ETASS, and APL/Johns Hopkins dual towed arrays are reviewed. Submarine towed-array programs from the early 1960s to today are described and a prediction of future towed-array development is presented.
 
Article
From August 1976 through December 1978, extremely low frequency (ELF) field strength and effective noise measurements were taken continuously in Connecticut and sporadically aboard operational submarines. This article summarizes the field strength measurements taken at both land (Connecticut) and sea (North Atlantic, Western Pacific) locations during January, March, April, and October 1977 and January/ February 1978. The main conclusion is that the average field strengths measured aboard the submarines (which were located at distances of 4-12 Mm from the Wisconsin Test Facility) are in excellent agreement with previous ELF measurements taken over similar paths. Anomalous ELF field strength variations were also correlated with geomagnetic activity. Interference between the direct and "round-the-world" paths was probably observed during the Western Pacific area daytime propagation period in early October 1977. ELF propagation effects were also observed during the February 13, 1978, significant solar particle event.
 
Article
From August 1976 through December 1978, extremely low frequency (ELF) field-strength and effective-noise measurements were taken continuously in Connecticut and sporadically aboard operational submarines. This paper summarizes the effective-noise measurements taken at both Connecticut and sea (North Atlantic, Norwegian Sea, South Atlantic equatorial area, Virgin Islands area, Hawaii area, Western Pacific, and Northwestern Pacific) locations during this period. The main conclusion is that there are often considerable differences in effective-noise levels measured at Connecticut and sea locations. The highest effective noise levels were measured in Connecticut during the summer months, while the lowest effective-noise levels were measured in the South Atlantic equatorial area during November.
 
Article
The history of the definition of salinity and the methods of computing It are traced from the beginning of the twentieth century until the present. Difficulties that have arisen in existing practices are discussed, in particular, the situation regarding reduction of in-situ CTD observations. The Practical Salinity Scale 1978 is an attempt to remove the shortcomings; it has been recommended for international acceptance. The basis for this new scale is an equation relating the ratio of the electrical conductivity of the seawater sample to that of a standard potassium chloride solution (KCI) at 15deg C atmospheric pressure. The samples used were prepared from standard seawater diluted with distilled water or evaporated by weight. Finally, the set of new equations for CTD data reduction is given, based upon the work of authors whose papers are appearing elsewhere in this volume.
 
Article
The Practical Salinity Scale (PSS) 1978 is defined only for salinities within the range 2-42. We have investigated the relationship between mass-determined salinity, electrical conductivity, and temperature for salinities between 0 and 2 with the aim of developing an extension to the Practical Salinity Scale 1978. The paper presents our data, on the basis of which the following correction is proposed to extend the validity of the equations defining the scale to the entire 0-42 range: S=summin{i=0}max{5} (a_{i}+b_{i}f(t))R_{t}^{i/2}-frac{a_{0}}{1 + 1.5x + x^{2}}-frac{b_{0}f(t)}{1+y^{1/2} + y + y^{3/2}} where f(t)=frac{(t-15)}{1 + k(t-15) x=400R_{t} y=100R_{t} and the constant a_{i}, b_{i} , and k are defind by the Practical Salinity Scale 1978.
 
Article
Three equations have been fitted to new data relating the electrical conductivity of seawater to the Practical Salinity Scale 1978. These equations have been designed for the reduction of in-situ measurements of temperature, pressure, and conductivity from anywhere in the world oceans. The standard deviation of the fit is roughly equivalent to pm0.0015permil in salinity depending on the pressure at which the data is taken and, as such is commensurate with the best accuracy attainable with modern instruments.
 
Article
This paper outlines the work done at the five laboratories which provided, at the request of the Joint Panel on Oceanographic Tables and Standards (JPOTS), the basic data for the new Practical Salinity Scale 1978. Interlaboratory agreement of a very high order was achieved. The new scale is in process of acceptance by all major oceanographic societies, at which time it will be officially recommended for all future reporting of oceanographic data. Copyright © 1980 by The Institute of Electrical and Electronics Engineers. Inc.
 
Article
The scale provides a precisely defined, unambiguous method that is universally applicable to all waters for determining the practical salinity from measurements of conductivity, temperature, and pressure. In the terminology of standards, it is highly desirable to have a scale that is also unique. The authors questioned whether measurements performed on a particular water sample at different temperatures would lead to the same value of practical salinity. They have investigated this problem by examining the behavior of natural seawaters from several oceans and conclude that the PSS provides a unique scale for salinity measurements for these waters within the bounds ±0.001 in salinity
 
Article
The use of CODAR by the University of Hamburg has extended to a wide variety of experimental and oceanographic activities over the last three years. These have ranged from Arctic studies from land and ships to observations of the Dead Sea, all yielding surface current data. Hardware improvements have been investigated, including IF amplifier changes and loop-antenna arrays for shipboard operation.
 
Article
This paper reviews X-band ocean microwave backscatter data from the LOGAN (LOw Grazing ANgle) experiment conducted on the Chesapeake Light Tower by the Naval Air Warfare Center. The data were collected under varied wind, sea, and swell conditions that provide some new insights into low-grazing-angle backscatter phenomena. Transient backscatter peaks called “sea spikes” have long been associated with deep-water breaking waves; however, they have yet to be fully reconciled with backscatter and hydrodynamic theories. New analysis techniques have been applied to the LOGAN data that take advantage of the unique characteristics of sea spikes and their dynamics. High-resolution Doppler spectra are organized relative to the space-time centroids of the sea-spike clusters and conditionally averaged by RCS strength. The mean Doppler variation of the strongest sea spikes then map the breaking-wave structure just as Doppler histories measured at moderate grazing angles map the dynamics of the dominant linear surface-wave components. While breaking waves are manifest to some degree in backscatter data at all grazing angles, a non-Bragg-scatter mechanism accentuates the crest scattering at low grazing angles. The phenomena potentially can be exploited for remote ocean sensing and imaging
 
Article
An overview is given of the July-August 1995 SWARM shallow-water internal wave acoustic scattering experiment. This experiment studied both acoustic propagation through and scattering by the linear and nonlinear internal waves found on the Mid-Atlantic Bight continental shelf, as well as the physical oceanography of the internal wavefield. In order that their goal of explaining the nature of the acoustic scattering should not be hindered by incomplete environmental knowledge, numerous instruments, both ship-deployed and moored, measured the acoustics, geophysics, and oceanography. In this paper, the authors show some of the results from the first year's analysis of the environmental and acoustic data. The environmental measurements, which are a key input to the analyses of the acoustic data, are given slightly more emphasis at this point in time. Some of the more interesting oceanographic, geophysical, and acoustical results the authors present are: evidence for the dominance of the lee-wave mechanism for soliton production, evidence for the “solibore internal tide” the “dnoidal wave” description of solitons, the inversion of chirp sonar data for bottom properties, propagation loss extraction from air-gun data, and the intensity and travel-time fluctuations seen in propagating acoustic normal modes. Directions for future research are outlined
 
Article
During July and August of 1996, the summer component of the New England shelfbreak front PRIMER experiment was fielded in the Mid-Atlantic Bight, at a site due south of Martha's Vineyard, MA. This study produced acoustic transmission data from a network of moored sources and receivers in conjunction with very-high-resolution oceanography measurements. This paper analyzes receptions at the northeast array receiver from two 400 Hz acoustic tomography sources, with the transmission paths going from the continental slope onto the continental shelf. These data, along with forward acoustic-propagation modeling based on moored oceanographic data, SeaSoar hydrography measurements, and bottom measurements, reveal many new and interesting aspects of acoustic propagation in a complicated slope-shelf environment. For example, one sees that both the shelfbreak front and tidally generated soliton internal wave packets produce stronger mode coupling than previously expected, leading to an interesting time-and-range-variable population of the acoustic normal modes. Additionally, the arrival time wander and the signal spread of acoustic pulses show variability that can be attributed to the presence of a frontal meander and variability in the soliton field. These and other effects are discussed in this paper, with an emphasis on creating a strong connection between the environmental measurements and the acoustic field characteristics.
 
Article
The present work describes the various corrections necessary in order to deduce ocean surface temperature from S -band microwave radiometer measurements and applies these results to a series of data obtained with a high absolute accuracy radiometer. Measurements made with a 2.65 GHz radiometer from an aircraft flown over the Chesapeake Bay area are presented and compared in detail with accurately obtained sea truth data. For the calm sea, it was found that the observed brightness temperature agreed well with that calculated from the known sea surface and atmospheric properties over a fairly wide range of surface salinity values (0.2 per mille to 25 per mille). For cases where the surface wind speeds are of the order of 7 to 15 knots, an excess brightness temperature was observed which is attributable to surface roughness and microscale surface disturbances. The excess brightness temperature dependence on wind speed was found to correlate to a certain extent with the rms wave slope dependence on wind speed.
 
Article
This paper presents some new results from measurements of seafloor reverberation and pulse spreading using horizontal and vertical line arrays. The principal objective of this paper is to extract useful geoacoustic and bottom-scattering parameters that apply over a large ocean area. Analysis is presented on reverberation data from the 2000 Boundary Characterization Experiment performed jointly with North Atlantic Treaty Organization (NATO) Undersea Research Center (NURC), Applied Research Laboratory (ARL) of Pennsylvania State University, Defence Research and Development Canada (DRDC), and Naval Research Laboratory (NRL). Sources were SUS charges and coherent pulses. The receivers were horizontal arrays used monostatically. Data were analyzed in bands from 80 to 4000 Hz. Highlights of the reverberant returns are discussed. The experiment site is the Malta Plateau area south of Sicily, a relatively flat heavily sedimented area, but with a rocky ridge to the east. An original aspect of this paper is the design and implementation of a new automated inverse method using towed-array data to accomplish that goal. For each data set, a multiple-step simulated annealing (SA) algorithm is used together with the Generic Sonar Model (GSM). After automatically adjusting bottom loss and scattering strength, good agreement is achieved between the diffuse reverberation data and model predictions in relatively flat areas. Model/data differences are generally correlated with bottom-scattering features. Since reverberation from SUS charges typically lasts 10-40 s or more, extracted parameters apply over wide areas. Independent acoustic measurements provided a basis for a comparison with extracted values. Local bottom-loss and backscattering measurements were made by Holland in these areas. Additionally, chirp-sonar measurements were analyzed by Turgut. A comparison of geoacoustic models obtained with their methods and with this one was quite good. Comparing transmission loss (TL) pred- - icted with Turgut's local inverse method and TL predicted with the method presented here gave answers that were usually within 3 dB of each other. Typical two-way time spreads of 0.25 s were seen at a range of 7.5 km, with normalized peak correlations of 0.5, and which were fairly consistent with predictions made using the inverse results
 
Article
Two intensive, high-resolution hydrographic surveys during April 2000 and May 2001 are used to characterize the thermohaline and current structure at the shelfbreak in the South China Sea. In 2000, a strong anticyclonic circulation was present in the northern portion of the South China Sea with strong onshore currents east of Dongsha Island. The flow became polarized along isobaths as it encountered shallow water, with northeastward flows of over 0.9 m/s along steep topography. The flow was driven by strong density contrasts between waters of the outer shelf and upper slope. Shelf water was both cooler and more fresh than the water offshore, which had salinities close to that of Kuroshio water. In contrast, the mean flow in the northern South China Sea was predominantly cyclonic in 2001. Flow over the slope was to the southwest at up to 0.2 m/s. The water mass properties of the outer shelf and upper slope were similar, so that there were not the strong cross-shelf density gradients present as in 2000. A potential difference between the water mass structure of the two years was the difference in cooling during the preceding winters. In December, 1999, unusually strong cooling may have resulted in cooler shelf waters relative to the following year. The ASIAEX study area may be a particularly sensitive region to both seasonal and interannual variability, as it is near a bifurcation point associated with the Kuroshio Intrusion into the South China Sea.
 
Article
This paper applies a Bayesian formulation to range-dependent geoacoustic inverse problems. Two inversion methods, a hybrid optimization algorithm and a Bayesian sampling algorithm, are applied to some of the 2001 Inversion Techniques Workshop benchmark data. The hybrid inversion combines the local (gradient-based) method of downhill simplex with the global search method of simulated annealing in an adaptive algorithm. The Bayesian inversion algorithm uses a Gibbs sampler to estimate properties of the posterior probability density, such as mean and maximum a posteriori parameter estimates, marginal probability distributions, highest-probability density intervals, and the model covariance matrix. The methods are applied to noise-free and noisy benchmark data from shallow ocean environments with range-dependent geophysical and geometric properties. An under-parameterized approach is applied to determine the optimal model parameterization consistent with the resolving power of the acoustic data. The Bayesian inversion method provides a complete solution including quantitative uncertainty estimates and correlations, while the hybrid inversion method provides parameter estimates in a fraction of the computation time.
 
Article
We present analyses of fluctuations seen in acoustic signals transmitted by two 400-Hz sources moored as part of the ASIAEX 2001 South China Sea (SCS) experiment. One source was near the bottom in 350-m deep water 31.3 km offshore from the receiving array, and the other was near the bottom in 135-m deep water 20.6 km alongshore from the array. Time series of signal intensity measured at individual phones of a 16-element vertical line array are analyzed, as well as time series of intensity averaged over the array. Signals were recorded from 2 May to 17 May 2001. Fluctuations were observed at periods ranging from subtidal (days) to the shortest periods resolved with our signaling (10 s). Short-period fluctuations of depth- and time-averaged intensity have scintillation indexes (computed within 3-h long windows) which peak at values near 0.5 during an interval of numerous high-amplitude internal gravity waves, and which are lower during intervals with fewer internal waves. The decorrelation times of the averaged intensity (energy level) are also closely related to internal wave properties. Scintillation indexes computed for unaveraged pulses arriving at individual phones often exceed unity.
 
Article
This correspondence presents a preliminary examination of the low frequency ambient noise field measured in the South China Sea component of the Asian Seas International Acoustics Experiment (ASIAEX), concentrating on the frequencies of 50, 100, 200, 400, 800, and 1200 Hz. A two-week-long time series of the noise at these frequencies is examined for structure in both the time and frequency domains. Three features of particular interest in these series are: 1) the noise due to a typhoon, which passed near the experimental site, 2) the weak tidal frequency variability of the noise field, which is probably due to internal tide induced variability in the propagation conditions, and 3) the vertical angle dependence of the noise, particularly as regards the shallow water "noise notch" phenomenon. The acoustic frequency dependence and the vertical dependence of the noise field are also examined over the course of the time series. A simple look at the noise variability statistics is presented. Finally, directions for further analysis are discussed.
 
Article
During the recent Asian Seas International Acoustics Experiment (ASIAEX), extensive current meter moorings were deployed around the continental shelf-break area in the northeastern South China Sea. Thirteen RADARSAT SAR images were collected during the field test to integrate with the in situ measurements from the moorings, ship-board sensors, and conductivity/temperatire/depth (CTD) casts. Besides providing a synoptic view of the entire region, satellite imagery is very useful for tracking the internal waves, locating surface fronts, and identifying mesoscale features. During ASIAEX in May 2001, many large internal waves were observed at the test area and were the major oceanic features studied for acoustic volume interaction. Based on the internal wave distribution maps compiled from satellite data, the wave crests can be as long as 200 km with an amplitude of 100 m. Environmental parameters have been calculated based on extensive CTD casts data near the ASIAEX area. Nonlinear internal wave models have been applied to integrate and assimilate both synthetic aperture radar (SAR) and mooring data. Using SAR data in deep water as an initial condition, numerical simulations produced the wave evolution on the continental shelf and compared reasonably well with the mooring measurements at the downstream station. The shoaling, turning, and dissipation of large internal waves at the shelf break have been studied and are very important issues for acoustic propagation.
 
Article
An inversion technique (IT) is developed and preliminarily tested using data from the 2001 IT Workshop. This technique was developed using TL versus range data collected by the harsh environments program (HEP) and provided through the workshop. However, the IT developed here applies to all sonar systems, active and passive. The sonar-independent portion of the IT consists of a simulated annealing algorithm to be developed by Neumann et al. constrained by an expert system called the Hamilton-Bachman Smart Rules (HBSR), which was developed by the authors. This expert system constrains the geoacoustic model being inverted to realistic Hamilton-Bachman-type values, curve shapes, etc. The sonar-specific module of the IT is chosen based on the sonar frequency and models available to run at those frequencies. Two measured data cases from the workshop are presented and, due to the HBSR, good solutions were acquired in less than 50 iterations.
 
Article
During the 2003-2004 winter season, the U.S. Office of Naval Research (ONR, Arlington, VA), sponsored a detailed in situ study of the mine burial process resulting from wave-seafloor-mine interaction at Martha's Vineyard Coastal Observatory (MVCO, Edgartown, MA). In total, 16 mine shapes were deployed. Six were the Forschungsanstalt der Bundeswehr fur Wasserschall und Geophysik (FWG, Kiel, Germany) burial registration mines using optical sensors, four others were equipped with acoustical sensors, and six were simple shapes. Repeated acoustic surveys and detailed sediment sampling were conducted to characterize the site and the burial status of all objects. This paper focuses on data from three recovered optical systems. The records show three roll events at all three registration mines, which are necessary for scour burial. Two systems experienced a fourth roll event. Results from earlier experiments suggest only three (four) stages of progressively increasing burial despite frequent successive burial and exposure cycles (some as short as 1 h). During these burial-exposure cycles changes of buried mine volume reached up to 80%. The only reasonable explanation is a change of sediment height of up to 40 cm relative to the stably lying mines. This requires new concepts. Cyclic burial changes that were observed simultaneously at different positions cannot be explained with existing models. The least difficult explanation is ldquounderwater sand stormsrdquo which are characterized by a high sediment suspension.
 
Article
The seven papers in this special issue deal with the effects of internal waves and internal tides on acoustic propagation and communication in shallow water, and geoacoustic characterization of the seabed.
 
Article
The seven articles in this special section represent a portion of the research that has been carried out under the umbrella of "Shallow Water Experiment (SW06)" off the coast of New Jersey.
 
Article
The Monterey Bay Aquarium Research Institute (MBARI, Moss Landing, CA) has developed a 54-cm-diameter (21-in) docking AUV and companion docking station. This program resulted in four consecutive successful autonomous homing and docking events in the open ocean, which included downloading data, uploading a new mission plan, recharging the battery, and complete power cycling of the AUV. We describe the design, simulation, and at-sea test of the homing and docking control system.
 
Article
Market studies by Hydro Products identified industry interest in a guide wire deployed package consisting of an RCV-225 remotely controlled vehicle with launcher and a strong dexterous manipulator for drill ship support in water depths to approximately 2000 ft ( sim 600 m). This paper discusses the design, production, and initial testing of a prototype unit. Anticipated capabilities provided for in the initial design include the ability to perform pre- and post-drilling site surveys, wellhead and riser television inspection, stabbing assist, AX/VX ring replacement, guide wire replacement assist, and debris removal. Provision for incorporation of further sensors and capabilities was given high priority. Future developments and plans for further testing are also enumerated.
 
Article
High-frequency bistatic sediment scattering experiment was conducted in the shallow waters off the east coasts of Korea. Acoustic data were taken as a function of grazing angle (30°, 45°, and 60°), scattered angle (30°, 45°, and 60°), and bistatic (azimuthal) angle (0°, 60°, and 120°). Besides a flat bottom it was artificially raked so as to produce directional ripples. The measured scattering strengths for a flat bottom were compared to model predictions of D.R. Jackson et al. (1986). The surface reverberation component is seen to dominate over the volume scattering part at the frequency of 240 kHz. Compared to the flat bottom case, the scattering strengths for directional ripples showed lower and higher variation depending on the ripple's orientation
 
Article
Ocean surface current gradients can be imaged by real and synthetic aperture radar (RAR/SAR) due to the so-called hydrodynamic modulation mechanism. This is the reason why underwater bottom topography and internal waves are visible on radar images. Several physical models exist for this imaging mechanism. When trying to obtain current information from SAR images, a problem arises: the imaging mechanism can be nonlinear. We propose to rewrite the classical modeling of the SAR underwater bottom topography imaging mechanism by using a Volterra series expansion. The Volterra model can be seen as a tool allowing us to study whether the imaging mechanism can be inverted or not. It is a transposition of a well-studied physical problem into a more explicit expression. The conditions for the inversion of the Volterra model are presented and a scheme for estimating the bathymetry from SAR images is described. The main property of the inversion algorithm is its independence from the physical model used for the mechanism
 
Article
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 ∼19 km from the receiving array.
 
Article
While the civil engineering facilities of hydraulic power plants such as dam, water intake, waterway, etc., are usually submerged, there are few effective methods for their inspection. So we at Mitsui Ocean Development and Engineering Co., Ltd. (MODEC) have developed a new remote-controlled inspection system named "MURS-300 MK II" (MODEC Unmanned Remote-Controlled Submersible for 300-m water depth) in cooperation with Tokyo Electric Power Co., Inc. This MK II system, which consists of a submersible vehicle with a TV camera and a still camera, a handling system, a control van, and a composite cable with optical fibers, was designed, developed, and successfully evaluated at the end of 1984. This new system will find many applications to the inspection of nuclear and thermal power stations, offshore platforms, etc., as well as hydraulic power plants.
 
Article
Parametric transduction offers valuable advantages for underwater acoustic communications. Perhaps the most significant benefit is the fact that high directivity is achieved by means of a physically small transmit transducer. This feature may, ultimately, be employed to permit long-range, low-frequency communication using a compact source. The high directivity is desirable to combat multipath propagation and to achieve data communications in water which is shallow by comparison with range. A real-time, high data-rate “model” differential phase shift keying (DPSK) communication system has been constructed and demonstrated. This system uses parametric transduction, with a 300-kHz primary frequency and a 50-kHz secondary frequency. Experimental results show that the system can be employed to combat multipath propagation in shallow water and can achieve high data-rate text and color image transmission at 10 and 20 kb s<sup>-1</sup> for 2-DPSK and 4-DPSK, respectively, through a transmission bandwidth of 10 kHz. The “model” system was developed to confirm performance predictions for a future, operational long-range link employing a 50-kHz primary frequency and a 5-kHz secondary frequency
 
Article
The design of a shallow-water synthetic aperture sonar (SAS) requires an understanding of key system and environmental issues. The main factors that limit SAS performance are as follows: micronavigation accuracy, where micronavigation is defined as the problem of estimating the acoustic path lengths to allow the focusing of the aperture; multipath effects; and target view angle changes. All of them can degrade shadow classification performance. Micronavigation accuracy is successfully addressed by the gyrostabilized displaced phase center antenna technique, which combines data-driven motion estimates with external attitude sensors. Multipath effects in shallow water are effectively countered by narrow vertical beams. Shadow blur induced by view angle changes is mitigated by increasing the center frequency, to reduce the SAS integration length while still maintaining the desired resolution and by designing the system with a minimum grazing angle of about 6deg to reduce shadow length. The combination of these factors led to the choice of a 300-kHz center frequency and of a multipath mitigation scheme that uses multiple vertical beams. Experimental results obtained with a sonar incorporating these features have produced SAS images with 1.6 cm times 5 cm resolution in range times cross-range and shadow contrast in excess of 5 dB, at ranges of up to 170 m in 20 m of water.
 
Article
Measurements of the ambient-noise field between 50 and 300 Hz with vertical arrays at 32°N (124°W, 136°W, and 150°W) have been made. Substantial differences in the vertical distribution of noise have been measured (especially at the higher frequencies), which can be interpreted in the context of attenuation by seawater sound absorption of coastal shipping noise. Under low wind-speed conditions, the vertical distribution of ambient noise is clearly concentrated within approximately ±15° of the horizontal. High wind speed has the effect of filling in the higher vertical angles, while leaving the level within the low-angular region unchanged
 
Article
Vertically polarized antenna temperatures of ore boats and their wakes were measured with a 35-GHz radiometer from a helicopter platform. The signatures of the boats appear to be independent of viewing angle at a temperature which is about 40 K cooler than the surrounding water. The signatures of the wakes show a dependence on viewing angle. Models for the antenna temperature are presented which fit the measured data to within the accuracy of the measurement and model parameters. These models are useful in themselves for predicting the antenna temperatures of targets in terms of parameters such as viewing angle, beam fill factor (BFF), antenna main beam efficiency, and target emissivity.
 
Article
This paper describes the life testing of a 35-kV power cable that will connect a single anchor leg mooring (SALM) buoy with a platform in several hundred feet of water. While there are many power cable installations to offshore platforms and between platforms, this system is unique because the cable will be constantly flexing in compression as the mooring buoy moves in the water. The buoy design includes an articulated leg with universal joints to which the cable is clamped. It is the loop in the cable where it crosses a universal joint that is flexed, and is a major cause of concern. To predict the effects of this constant flexure while energized, a flex simulator and electrical circuit were devised to duplicate the service environment as closely as possible. This paper describes the cable system, the test apparatus and procedure, and the results obtained.
 
Article
The concentration of the potassium chloride solution (KCI) which has the same conductivity as 15deg C at P79 standard seawater corrected to 35.0000permil has been evaluated. The variation of the conductivity ratio of KCI solutions to standard seawater ( 35permil ) has been measured between 14.8 and 15.2deg C for KCI solutions whose concentration varies from 32 to 33 g.kg<sup>-1</sup>.
 
Article
The ratios Z_{K,t} of electrical conductivities of potassium chloride (KCI) solutions of known concentration ( K ) to standard seawater at the same temperature have been measured at 15deg C and 24deg C for solutions with Z_{k,15} between 0.96 and 1.04. The "normal" concentration ( N or K_{N} ) giving Z_{N,15}= 1 was found to be K_{N} = 32.4356 gKCI/kg solution. The effect of temperature on Z_{N,t} was measured over the range 15deg C to 30deg C. Equations are given for KCI concentration as a function of Z_{15} and the inverse function, for Z_{15}/Z_{24} as a function of Z_{24} (to allow use of a laboratory salinometer for the KCI-seawater comparisons), and Z_{N,t} as a function of temperature.
 
Article
Field data were analyzed from a simultaneous deployment of two 3D-ACM WAVE instruments; one on a fixed seabed frame in the nearshore zone, and the other further offshore on a taut-wire mooring. An intercomparison of measurements of vertical and horizontal wave-orbital currents with pressures was used to evaluate the velocity sensor response under field conditions. Results using the fixed frame have validated the measured horizontal wave-orbital velocities, but found the vertical velocities to be less coherent with the pressure time-series. The influence of the instrument mooring system on the velocity measurements was investigated. The oscillation of the taut-wire mooring was found to influence the magnitude of the measured horizontal wave-orbital velocities and induce a phase lag between velocity and sea-surface elevation. Examination of other data from similar taut-wire moorings indicates a systematic relationship between the length of the mooring cable and the measured phase lag, consistent with the behavior of the mooring system considered as a forced, linearly damped oscillator. A comparison was made between the spectra of wave direction derived from both velocity and pressure data with that derived solely from velocity data. The results show a high coherence for the fixed mooring, but significant directional variability in the higher frequencies (>0.13 Hz) on the taut-wire mooring we employed, which we attribute to the mooring oscillation. The analysis further indicates that on taut-wire moorings, the spectra of wave direction should be resolved solely from velocity data. Using these findings, directional wave spectra were produced for the nearshore and offshore sites from 233 coincident events over a two-month period, and these data are presented in a time-averaged spectral format
 
Article
DOLPHIN 3K is a tethered remotely operated vehicle (ROV) system for ocean bottom surveys down to a depth of 3300 m. The system will be completed in fiscal year 1986. This paper describes the design of the system, and analyzes the maneuverability of the vehicle and the transmission performance of the optical fiber data communication system.
 
Article
A descriptive analysis of reverberation statistics is presented for data taken during the 2001 Acoustic Clutter Reconnaissance Experiment, which was conducted on the Office of Naval Research (ONR) STRATAFORM area off the coast of New Jersey. Large area plots of reverberation versus topography are presented as a lead-in to describe the statistics of the reverberation and clutter that were observed during this experiment. A comparison of polar plot appearance of spikiness with a measure of non-Rayleigh behavior seems to correlate reasonably well and suggests that the polar plots may be useful as such an indicator of non-Rayleighness. Statistical analysis of the reverberation showed that a moderate-to-large portion of the data examined were nearly Rayleigh and that most of the data (Rayleigh-like and non-Rayleigh) were well fit by the K distribution. The bistatic data were seen to be uniformly and significantly more non-Rayleigh than the monostatic data. This disparity is believed to be mostly accounted for by the lower reverberation-to-ambient noise power levels in the monostatic data and the smaller vertical beamwidth of the bistatic source, rather than having arisen from the bistatic geometry. Analysis of the shape parameter of the K distribution as a function of bandwidth illustrated the "bandwidth" effect where the shape parameter first decreases inversely proportional to bandwidth, but then increases in a trend back toward the Rayleigh distribution at higher bandwidths. The shape-parameter estimates are seen to be well fit by the elongated patch model of Abraham and Lyons. The monostatic data were observed to have a minimum occurring at a smaller bandwidth than for the bistatic data, a result explained by the larger time spread of the multipath expected for the monostatic source owing to its larger vertical beamwidth. Analysis of a small amount of data from the 2003 Acoustic Clutter Experiment, recently conducted on the New Jersey Shelf, predicts a smaller bandwidth for the minimum of the shape-parameter curve compared to the 2001 data. It is believed that the sound-speed profiles in 2003 lead to more bottom interaction than in 2001 and, therefore, produced a larger time spread in the multipath, leading to a minimum occurring at a lower bandwidth. The resu- lts of this paper indicate that many of the phenomena observed in the analysis of reverberation-envelope statistics may be explained by appropriately considering the effects of propagation in conjunction with the sonar system with which the environment is probed.
 
Top-cited authors
Arthur Baggeroer
  • Massachusetts Institute of Technology
J.G. Proakis
  • University of California, San Diego
J.F. Lynch
  • Woods Hole Oceanographic Institution
John Bruce Davies
  • University of Strathclyde
Dana Yoerger
  • Woods Hole Oceanographic Institution