Showing papers in "IEEE Journal of Oceanic Engineering in 1985"
TL;DR: In this article, a recent extension of sliding mode control is shown to handle nonlinearities, is highly robust to imprecise models, explicitly accounts for the presence of high-frequency unmodeled dynamics, and produces designs that are easy to understand.
Abstract: underwater vehicles present difficult control-system design problems due to their nonlinear dynamics, uncertain models, and the presence of disturbances that are difficult to measure or estimate. In this paper, a recent extension of sliding mode control is shown to handle these problems effectively. The method deals directly with nonlinearities, is highly robust to imprecise models, explicitly accounts for the presence of high-frequency unmodeled dynamics, and produces designs that are easy to understand. Using a nonlinear vehicle simulation, the relationship between model uncertainty and performance is examined. The results show that adequate controllers can be designed using simple nonlinear models, but that performance improves as model uncertainty is decreased and the improvements can be predicted quantitatively.
513 citations
TL;DR: In this paper, a new spectrum model for the ocean surface was proposed and the two unknown parameters in this spectrum were determined by fitting it to radar observations, and it was shown that this spectrum combined with two-scale scattering theory can predict much of the observed dependence of the radar cross section on radar frequency, polarization, angle of incidence, and wind velocity at incidence angles in the 0\deg-70\deg range.
Abstract: A new spectrum model for the ocean surface is proposed. We determine the two unknown parameters in this spectrum by fitting it to radar observations. We find that this spectrum combined with two-scale scattering theory can predict much of the observed dependence of the radar cross section on radar frequency, polarization, angle of incidence, and wind velocity at incidence angles in the 0\deg-70\deg range. The spectrum model is combined with a model for swell to examine the effect of swell on the radar cross section. We find that the effect of swell is significant for low radar frequencies ( L band) and near normal incidence but can be nearly eliminated by using higher frequencies ( K_{u} band) and large angles of incidence ( \approx 50\deg ).
282 citations
TL;DR: In this article, the effect of random phase errors in the phase shifters which are used in an antenna array to steer the beam in the look direction, and analyzes the performance of the optimal processor which maximizes the output SNR by deriving the expressions for the output signal power, residual interference power, and the array gain as a function of the variance of these errors.
Abstract: The paper considers the random phase errors in the phase shifters which are used in an antenna array to steer the beam in the look direction, and analyzes the effect of these errors on the performance of the optimal processor which maximizes the output SNR by deriving the expressions for the output signal power, residual interference power, output SNR, and the array gain as a function of the variance of these errors. The paper also considers the phase quantization error which arises in the digital phase shifters and shows how the performance of the optimal processor depends on the number of bits of the digital phase shifters.
79 citations
TL;DR: The National Data Buoy Center (NDBC) of the National Oceanic and Atmospheric Administration (NOAA) deployed a 10m-diameter discus-type hull in the Pacific Ocean some 185 km southwest of Los Angeles, California, in April 1984 as discussed by the authors.
Abstract: The National Data Buoy Center (NDBC) of the National Oceanic and Atmospheric Administration (NOAA) deployed a 10-m-diameter discus-type hull in the Pacific Ocean some 185 km southwest of Los Angeles, California, in April 1984. Aboard this hull was an electronic system capable of acquiring, processing, and transmitting to shore directional wave measurements. For this system to produce accurate data, a number of factors had to be taken into account. These factors included noise, amplitude and phase alterations due to mechanical and electrical components, and magnetic fields arising from the hull. Comprehensive calibration and verification techniques were developed and applied to ensure data quality. The system configuration is described with emphasis on the methods used in the data processing to correct for the various factors. Examples of the resulting corrected data are given.
64 citations
TL;DR: The AAFE RADSCAT/ocean wind signature deduced from the complete data set was analyzed in this article, which was used to model the relationship between the Ku-band radar signature and the ocean-surface wind vector.
Abstract: 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.
62 citations
TL;DR: In this paper, the authors quantitatively study the problem of partial insonification by a collimated sound beam and obtain high-frequency approximations of the resulting integrals, obtained by means of the saddle point method, showing the relative importance of the scattering centers located at the beam's specular reflection points, or at the edges of the spots that the beam shines on the scatterers.
Abstract: An object that is partially insonified by a collimated sound beam may have a scattering cross section sometimes much larger than when the object is totally covered by the incident beam. We quantitatively study this partial insonification problem here, under the classical method of physical optics. The importance of this study stems from the fact that partial coverage of the target by the beam is the situation most likely to occur in many cases of practical importance. We consider several basic target shapes partially insonified by finite beams. These shapes include the spherical, the infinite and finite cylinder, the flat plate, and the capped sphere. High-frequency approximations of the resulting integrals, obtained by means of the saddle-point method, show the relative importance of the scattering centers located at the beam's specular reflection points, or at the edges of the spots that the beam shines on the scatterers. The physical-optics method is extended to obtain formulas for the bistatic cross sections of partially insonified objects. The results are numerically evaluated and graphically displayed in many pertinent instances and compared to the predictions of approaches, such as the Fresnel-zones method and the Geometrical Theory of Diffraction (GTD). The predictions of the physical-optics method have all the advantages and deficiencies of this method and, with very minor modifications, hold equally well for the partial illumination of objects by beams of electromagnetic radiation.
59 citations
TL;DR: In this paper, an acoustic transceivers have been designed and built to measure the mean currents between two points separated by 300 km, and the equipment functioned satisfactorily during a sbort test conducted during 1983.
Abstract: By simultaneously transmitting acoustic pulses in opposite directions between two points in midocean, one can separate the effects of ocean currents on acoustic propagation from the effects of sound-speed structure. Reciprocal acoustic transmissions can therefore be used to measure ocean currents. Acoustic transceivers have been designed and built to measure the mean currents between two points separated by 300 km. The equipment functioned satisfactorily during a sbort test conducted during 1983. Preliminary analysis of that experiment has yielded differential travel times that appear reasonable, but more work is required to relate the differential travel times to meaningful ocean-current estimates.
58 citations
TL;DR: In this paper, high-precision densely sampled maps of ice motion were derived by tracking ice features to determine the small-scale spatial variability of ice deformation using digital SEASAT synthetic aperture radar (SAR) imagery.
Abstract: Using digital SEASAT synthetic aperture radar (SAR) imagery, high-precision densely sampled maps of ice motion have been derived by tracking ice features to determine the small-scale spatial variability of ice deformation. The digital SAR imagery was processed to remove geometric distortions and located on the Earth to an accuracy of about 100 m utilizing an algorithm based on the spacecraft orbital data and the characteristics of the SAR data collection system, independent of attitude information or ground reference points. Radiometric enhancement of the imagery using a variable linear stretch algorithm was performed to remove a system-related gradient and improve the identification of sea ice features. Using ice features common to an overlapping pair of images, vector plots of ice motion were then produced. Examples of ice motion are shown in the marginal ice zone and in the central ice pack where mean displacements of 15.3 km/day and 5.0 km/day were measured, respectively. Considering errors in Earth location with those in feature identification an overall error of 150-200 m in displacement measurements was estimated. The ice motion vector plots indicate a high degree of spatial deformation, demonstrating the potential value of spaceborne SAR data for production of precision large-scale maps of ice displacement with a spatial resolution of ice deformation on scales much less than 100 km.
51 citations
TL;DR: In this article, the authors investigated statistical properties of certain parametric methods for array processing in wave fields and applied them to define approximate likelihood functions to be maximized for source-parameter estimation.
Abstract: Statistical properties of certain parametric methods for array processing in wave fields are investigated. Potential applications are the classic location problem in underwater acoustics and wavenumber-spectrum analysis in geophysical work. Asymptotic normality of Fourier-transformed outputs of an array of sensors is applied to define approximate likelihood functions to be maximized for source-parameter estimation. Usually, the parameters are those of the spectral-density matrix. Liggett's estimates are approximations of maximum likelihood estimates in this sense. Another possibility is to use conditional likelihood functions. As a consequence, the source parameters can be found by solving nonlinear-regression problems. Approximate solutions of the latter, which enhance certain simple estimates by some iterations related to Fisher's scoring method, compare favorably with Liggett's estimates. Key Words-Array processing, beam forming, applications in passive sonar, radar and geophysical work; parametric methods: maximum likelihood and nonlinear regression; theoretical study and numerical experiments.
49 citations
TL;DR: In this paper, a model for Doppler spectral characteristics of radar sea scatter for low grazing angles is proposed, based on the two-scale model for radar scatter, with scatterer motions hypothesized as due to the orbital wave velocity of the large-scale waves, Stokes and wind drift currents, and the phase velocity of small-scale Bragg scatterers.
Abstract: A model is formulated for Doppler spectral characteristics of radar sea scatter for low grazing angles, and is compared with previous radar measurements reported in the literature. The Doppler model is based upon the two-scale model for radar scatter, with scatterer motions hypothesized as due to the orbital wave velocity of the large-scale waves, Stokes and wind drift currents, and the phase velocity of the small-scale Bragg scatterers. Expressions for Doppler shifts due to these motions are derived, and are given as a function of wave height, wave period, and wind speed. Although this model appears to account for the peak Doppler shift of the sea-scatter Doppler spectrum for vertical polarization, it is insufficient to describe horizontally and cross-polarized data, which have larger mean Doppler shifts. However, these two cases are found to scale very closely with the nearly simultaneous vertically polarized data for the variety of environmental conditions reported. Implications of the extension of these results to higher-angle remote-sensing applications are discussed.
47 citations
TL;DR: In this paper, the results of a general theoretical investigation of three commonly used types of inductive conductivity sensors, i.e., the single transformer, the double transformer, and double transformer with an additional loop, are presented.
Abstract: The results of a general theoretical investigation of three commonly used types of inductive conductivity sensors, i.e., the single transformer, the double transformer, and the double transformer with an additional loop, are presented. The resulting formulas describe the dependence of the sensor output signal not only on the conductivity of the seawater but also on the parameters of the electrical circuit, among them the permeability of the transformer core(s), which-unlike the other parameters-shifts considerably during oceanographic in situ measurements. A mathematical discussion of these formulas shows that for certain circuit configurations, the sensor output is independent of changes in permeability. Most of these configurations form the basis of existing oceanographical conductivity sensors, among them the "classical" sensors developed by H. Hinkelmann [3], [4], and by N. L. Brown [14], while some others make evident further possibilities for eliminating the unwanted effects of shifting permeability. In the era of microelectronics, the latter might lead to a reassessment, especially of the single transformer-type sensor.
TL;DR: The basic approach is based on the idea of minimizing the mean-square deviation between the desired look-direction response and the response of the processor over a frequency band of interest.
Abstract: In this paper, a new approach to the design of broad-band time-domain element space antenna array processors is presented. The basic approach is based on the idea of minimizing the mean-square deviation between the desired look-direction response and the response of the processor over a frequency band of interest. With this approach, three types of presteering can be handled: no presteering, coarse presteering, and exact presteering. The elimination of presteering lime delays is important in a digital implementation of antenna array processors. The relationship that the new processor has to other broad-band processors is explored and the significance of the parameters associated with the new processor is established. Furthermore, the approach presented enables various types of errors and mismatches between signal model and actual scenario to be incorporated in the problem formulation.
TL;DR: In this article, the principles of radar scattering from the sea are outlined along with some recently discovered questions, and some principles that can be used in evaluating the various theories are presented, along with brief outlines of the major conflicting theories.
Abstract: Radar remote sensing of the ocean has been the subject of research for about 20 years. Spaceborne radar altimetry and scatterometry are approaching maturity, and synthetic-aperture radars (SAR) show great promise. The principles of radar scattering from the sea are outlined here, along with some recently discovered questions. For wind-vector scatterometry, the principle is presented, and remaining uncertainties are outlined. Principles of SAR imaging of moving targets, and particularly the ocean surface, are outlined. The theory of SAR wave imaging is the subject of considerable controversy, and some principles that can be used in evaluating the various theories are presented, along with brief outlines of the major conflicting theories. Other uses of SAR images are discussed briefly, with a theory to explain the bathymetric expression outlined.
TL;DR: In this paper, ship noise received on a horizontal array towed behind a ship is used as a potentially diagnostic tool for estimating local acoustic bottom properties, and the beamforming output is readily interpreted by relating it to the Green's function of the acoustic wave equation.
Abstract: Ship noise received on a horizontal array towed behind the ship is shown to be useful as a potentially diagnostic tool for estimating local acoustic bottom properties. In numerical simulations, tow-ship noise which bounces off the bottom is processed on a beamformer that shows the arrival angles; the beamformer output is readily interpreted by relating it to the Green's function of the acoustic wave equation. Simple signal processing is shown to be sufficient to extract the propagation angles of the "trapped" (i.e., propagating) modes of the acoustic waveguide. By relating the trapped modes to a basic geophysical model of the bottom, one can predict acoustic-propagation conditions for a particular bottom-interacting ocean acoustic environment.
TL;DR: In this article, field trials of an optical scanner for measuring directional slopes of the sea surface have been carried out at the Research Pier of the Coastal Engineering Research Center (CERC), and preliminary results include upwind-downwind and crosswind components of the mean-square slopes under various wind, swell, and atmospheric stability conditions.
Abstract: Field trials of an optical scanner for measuring directional slopes of the sea surface have been carried out at the Research Pier of the Coastal Engineering Research Center (CERC). Preliminary results include upwind-downwind and crosswind components of the mean-square slopes under various wind, swell, and atmospheric stability conditions.
TL;DR: In this paper, the stable nonlinear method (SNLM) was proposed to resolve and localize discrete sources in the presence of correlated noise, system phase errors, and multipath arrivals.
Abstract: Most nonlinear high-resolution bearing estimators are unstable in the presence of correlated noise, system phase errors, and multipath arrivals because they inadvertently place too much emphasis on unstable eigenvectors of the cross-sensor correlation matrix. For moderately correlated noise there will be sufficiently many stable eigenvectors to resolve and localize discrete sources. A method is given (the "stable nonlinear method" or SNLM) whereby reweighting of the eigenvectors is achieved implicitly, without actual calculation of the eigenvectors. This SNLM is compared with Capon's maximum likelihood method (MLM) in simulations of correlated noise, partially correlated signals, and phase errors, and is shown to provide good stability in the cases considered.
TL;DR: In this paper, a wave height meter using a simple microwave Doppler radar is proposed to measure oceanic waves effectively while the ship is steaming. But it was first applied to the measurement of the variation of water level generated in a wave tank, which suggested that it was adequately applicable to the measurements of oceanic wave.
Abstract: A wave-height meter using a simple microwave Doppler radar, \simeq10 mW in power and 10.525 GHz in frequency, is proposed so that we can measure oceanic waves effectively while the ship is steaming. It was first applied to the measurement of the variation of water level generated in a wave tank, which suggested that it is adequately applicable to the measurement of oceanic waves. A field test was carried out off the cape of Nojimazaki by installing the Doppler radar 5 m above the sea level at the bow of the ship. The result agreed reasonably well with that measured simultaneously by the ultrasonic wave-height meter installed at the same position. Another test is running successfully on a larger ship with the wave-height meter installed at 9 m above the sea level. The significant wave height measured by the present meter is being compared with that observed visually by the navigation officers.
TL;DR: The Times Atlas of the Oceans as mentioned in this paper provides a concise and thorough overview for the technically oriented person, which is useful for managers, engineers, and scientists who work in such diverse areas of d e a n science and engineering as acoustic system design, fisheries management, offshore resources management, and civil engineering.
Abstract: Alastair D. Couper, the editor of The Times Atlas of the Oceans, states that the purpose of this work is to present an informative view of the resources of the last major frontier to the Marine specialist, the policymaker, and any intelligent person who desires lmowledge about the oceans. To a large extent, this atlas has accomplished its objective admirably. This atlascan be of value to managers, engineers, and scientists who work in such diverse areas of d e a n science and engineering as acoustic system design, fisheries management, offshore resources management, and civil engineering, and whose primary discipline may not have included a detailed s&dy of the “ocean basins” and the “ocean atmospheric system.” The atlas provides a concise and thorough overview for the technically oriented person. In particular, I found the self-contained overviews (with all terms defined) of the ocean zones, the hypographic curve, and magnetic seafloor dating and the summaries of the ocean crust, layering, and sedimentation both useful and informative. The portion of the atlas entitled “The Ocean-Atmosphere System” is an especially intriguing section, reminiscent of the fact that weather is something we all live with but few of us know anything about. If you think you have the need for a quick reference to tsunamis, monsoons, cyclones, water spouts, tides, or surges, then you will find a good treatment in this atlas. The treatment again is self-contained, that is, the graphics and written material define, either by illustration or text, all terms used by the authors. The atlas features a unique and imaginative use of color graphics, charts, and tables in order to present subject areas in a readable and quickly graspable manner. In most instances the authors have been successful in treating complex subjects on two pages, mostly with beautiful color graphs, charts, and pictures. This will undoubtedly please most people who are program managers, bureaucrats, and/or policyrnakers. An example would be the treatment of submarine strategy and defense. Consistent imaginative definitions of symbols, abbreviations, and good graphics enables a numerical comparison of submarine forces, missile ranges, evolution of the submarine, the use of mi nes, and a comparison of ship class sizes and their geographic distribution, all on two pages. This won’t replace “Jane’s Fighting Ships,” but it may be the place to start for the quick answer to a question or a concise overview. The atlas, of course, reflects the opinions of its authors, which in many cases appear reasonable and accurate. However, in a few instances the attempt of being concise reslilts in an oversimplification of the subject, sich as the section on Naval operations. In several instances the material is simply too complex, such as the Summary of “World Operations and Gunboat Diplbmacy” from 1946 to 1980. The atlas presents information concerninglife in the sea. The “Oceans and Life” section discusses the closely interrelated lifeforms ranging from the vegetable phytopladkon through complex food chains to the large fish .and mammals (all illustrated with excellent photographs of the life-forms). The “Living Resources” and “The Fisheries” present an interesting oyerview of the use and explanation of these resources by man. Of piqticular interest was my junior high school friend’s (Brad Colten) ability to use the graphic description of pelagic and demersal fishing g&s (defined in the atlas) with minor assistance. The graphics were readily understood after careful examination and with minor assistance Brad could grasp the essence of where the fish he eats originate and how they are caught. I found that in most instances the interested @ard to find) high school student could use the atlas and I was especially pleased to discover that most liberal arts majors could follow the graphic illustrations pertaining to technical subjects. Thus the atlas may have a more general use than in the technical office. The atlas has a comprehensive set of appendixes, a glossary, sources used in preparation of the atlas, and a bibliography. The bibliography appears to be adequate, however, what it does not provide is guidance to the interested reader on which references he should pursue to obtain additional knowledge. In other words, the atla.s provides a good start and overview but does not direct the reader to additional sources by level of difficulty and topic. Nevertheless, this atlas would be a worthwhile addition to the office or home library.
TL;DR: In this paper, the asymptotic probability of detection was compared in the frequency domain based on the APD criterion with the normalized fourth-order and kurtosis estimates.
Abstract: Several detection statistics are compared in the frequency domain based on the asymptotic probability of detection (APD) criterion. They include second-order, fourth-order, normalized fourth-order, and kurtosis estimates. The results show that for randomly occurring signals which can be characterized as non-Gaussian, the fourth-order, normalized fourth-order, and kurtosis estimates can have higher asymptotic probability of detection levels compared with second-order estimates. But only for the normalized fourth-order and kurtosis estimates do the results seem significant. Moreover, if a second-order estimate of the noise is available to normalize a fourth-order estimate of signal and noise, the resultant normalized fourth-order estimate has higher asymptotic probability of detection levels even for Gaussian signals. This result holds only when there is a significant positive covariance between the numerator and the normalizing noise sample in the denominator. On the other hand, if an independent noise sample is used to normalize a second-order or fourth-order estimate, the overall performance based on the asymptotic probability of detection will be degraded compared with the unnormalized second-order or fourth-order estimates, respectively.
TL;DR: In this article, a model describing the beam pattern is used to predict the number, position, and height of these sidelobes, and a simple interpolation scheme is proposed to reduce the height of the sidelobe.
Abstract: In conventional time-domain beam forming with sampled receiver outputs, the delays required to steer a beam in a given direction can only be approximated to within the nearest half sampling interval. For a linear array of equispaced receivers, and for certain directions, these errors give rise to high isolated sidelobes in the beam pattern. A model describing this beam pattern is used to predict the number, position, and height of these sidelobes. Degradation of the height of the main lobe is also considered. For coarse quantization, and in the absence of interpolation, the model suggests a recursive beamformer structure which significantly reduces the number of additions required. A simple interpolation scheme which reduces the height of these sidelobes is discussed and an Efficient scheme for implementing such interpolation is given.
TL;DR: In this paper, a theoretical analysis of the scattering of high-frequency (HF) electromagnetic waves from rough surfaces is proposed, when applied to a model for the ocean surface, leads to new predictions of its second-order backscattered radar cross section in addition to those provided by existing theories.
Abstract: A theoretical analysis of the scattering of high-frequency (HF) electromagnetic waves from rough surfaces is proposed. The analysis, when applied to a model for the ocean surface, leads to new predictions of its second-order backscattered radar cross section in addition to those provided by existing theories. Some of the predictions of the theory have already been verified experimentally.
TL;DR: In this paper, the authors used an array of moored current meters and an HF ocean surface radar to investigate the line broadening on the radar spectra caused by the velocity distribution within the radar target cell.
Abstract: Experimental results from an array of moored current meters and an HF ocean surface radar support the idea that line broadening on the radar spectra is caused by the velocity distribution within the radar target cell. The experiment was done in the wake of a small island where the velocity variations were severe. An estimate is made of the line broadening which can be expected. In a turbulent flow with dissipation rate of the order \epsilon \sim 10^{-10}m^{2}s^{-3} and target cell size 1 3000 m, the line broadening is \Deltaf \sim 10^{-3} Hz. This would be resolved with a radar time series of \sim 20 min and indicates that the HF ocean surface radar technique has potential in the observation of surface velocity distributions.
TL;DR: The results of this study show that the asymptotic performance of the Doppler system examined is approximately 25 percent above a theoretical lower bound.
Abstract: Active Doppler sonar systems are gaining popularity as a method to profile remotely the oceanic velocity field. Estimation of the variance with which an ideal single.beam sonar system measures relative Doppler motion is the subject of this paper. Theoretical formulations, simulated reverberation data, and sea data are considered to determine this variance. The sea data considered in this paper were selected carefully to avoid performance degrading physical/instrumental phenomena and bias corrected to remove further instrumental effects. Asymptotic performance, determined in this research, is realized when instrumental and physical phenomena do not measurably affect experimental performance. Oceanic and simulated data sets are processed with several velocity-estimation algorithms that are implemented in existing sonar systems. These algorithms are compared against each other and the velocity-estimation standard-deviation results tabulated. The algorithms are shown to possess similar performance characteristics when simulated, and sea data are processed in spite of the fact that some of these algorithms are suboptimal from a theoretical viewpoint. The results of this study show that the asymptotic performance of the Doppler system examined is approximately 25 percent above a theoretical lower bound.
TL;DR: In this paper, two single-sensor piezometer probes, 8 mm in diameter, were developed for deep-ocean geotechnical investigations, and tested in a hyperbaric chamber pressurized to 55 MPa (8000 psi).
Abstract: Two single-sensor piezometer probes, 8 mm in diameter, were developed for deep-ocean geotechnical investigations. These probes were tested in a hyperbaric chamber pressurized to 55 MPa (8000 psi). Testing was performed for a period of five weeks under high hydrostatic pressure with the probes inserted in reconstituted illitic marine sediment. Small differential pore-water pressures were generated in response to both mechanically and thermally generated forcing functions. During deep-ocean simulated pressure tests, the sensors exhibited excellent sensitivity and stability. These developments in piezometer-probe technology provide a quantitative means of assessing important geotechnical parameters of fine-grained seabed deposits.
TL;DR: In this paper, X-band synthetic aperture radar (SAR) imagery of the Goto Islands of Japan was digitally analyzed to extract air-sea interaction parameters and to assess the potential of texture measures in analysis of SAR ocean imagery.
Abstract: X -band synthetic aperture radar (SAR) imagery of the Goto Islands of Japan was digitally analyzed to extract air-sea interaction parameters and to assess the potential of texture measures in analysis of SAR ocean imagery. Wind direction is extracted from wind rows, wind streaks, and random turbulence patterns observed in the SAR imagery. Sea-state parameters are either extracted directly from the imagery or estimated using the extracted information in previously established empirical formulas. A convenient method of digitally presenting imagery, local power spectra, and the extracted/estimated parameters is presented. Texture analysis based on gray-level co-occurrence (GLC) matrices is applied to SAR ocean imagery. The inertia measure is shown to extract similar information to the power spectrum. The cluster-shade measure is shown to be sensitive to image phase.
TL;DR: The use of free-fail penetrators is now actively considered by many national and international organizations as a possible option for the safe final, disposal of high-level radioactive waste in vitrified form within deep-ocean sedimentary geological formations.
Abstract: The use of free-fail penetrators is being now actively considered by many national and international organizations as a possible option for the safe final, disposal of high-level radioactive waste in vitrified form within deep-ocean sedimentary geological formations. The present paper describes methods and results of a study aimed at highlighting the effects of a number of different parameters on penetrator performance. This work is intended as a preparation of a new series of tests to be carried out during 1984-1986 to assess the present modeling capabilities in more detail. An initial experiment carried out in March 1983, using large model penetrators (3.25 m long, 0.325 m diameter, weight 1.8 tons in air) has successfully demonstrated that it is feasible to design free-fall vehicles which are capable of reaching terminal velocities of 45-50 m/s and embedding themselves up to thirty meters in clayey deep-sea sediments.
TL;DR: In this article, the authors describe the acoustic-communication, electrical-control, data-acquisition, and mechanical-control systems developed and tested for use on the In situ Heat Transfer Experiment (ISHTE) lander.
Abstract: A lander is being designed to perform a year-long in situ Heat Transfer Experiment (ISHTE) on the deep seafloor. This paper describes the acoustic-communication, electrical-control, data-acquisition, and mechanical-control systems developed and tested for use on the ISHTE lander. The lander's functions include implanting a heat source in the deep ocean clay, monitoring the thermal field, supporting geotechnical and geochemical experiments, and recovering undisturbed sediment core samples. Once the lander is deployed, the acoustic-communication link is the only connection between it and a surface ship. The acoustic-communication link is used to track and send commands to the lander and to transmit experiment data and lander status to a surface ship.
TL;DR: In this paper, it is proposed that wind-generated solitons (hydraulic "jumps"), moving nondispersively on the thin wind-driven drift layer of wind-excited (ocean) wave surfaces, are important products of the process whereby wind-wave surfaces are generated; potentially significant in low-angle high-frequency (for example, X -band radar) scattering from such surfaces; and a plausible mechanism responsible for the observed anomalous (vis-a-vis conventional theory) large backscatter returns in underwater acoustics when high frequencies
Abstract: It is proposed that wind-generated solitons (hydraulic "jumps"), moving nondispersively on the thin wind-driven drift layer of wind-excited (ocean) wave surfaces, are: a) important products of the process whereby wind-wave surfaces are generated; b) potentially significant in low-angle high-frequency (for example, X -band radar) scattering from such surfaces; and c) a plausible mechanism responsible for the observed anomalous (vis-a-vis conventional theory) large backscatter returns in underwater acoustics when high frequencies and small grazing angles ( \phi ) are employed, in the absence of significant near-surface bubble layers [1]. When the local atmospheric conditions are such that significant bubble densities are created (principally by breaking waves), the resulting bubble layer will dominate and mask these solitons, in underwater acoustic scattering. They should, however, remain effective at low angles and high frequencies in electromagnetic (EM) or radar scattering from above the surface, unless surface spray is heavy. A qualitative mixed linear-nonlinear model of ocean-wave generation is briefly described, a key element of which is the production of soliton ensembles. These are created, and destroyed, on the moving gravity-wave "facets" of the developing wind-wave surface, along with accompanying capillary components. Unlike these gravity-capillary waves, which are dispersive, the solitons are nondispersive, i.e., move at constant speed, on the thin (moving) wind drift layer generated upon the upper part of the water surface. A variety of experimental data and evidence [2]-[7], [10]- [14], [17] is cited and discussed in support of the proposed soliton mechanism. Included are recent results for acoustic backscatter at small grazing angles in the frequency range 5-20 kHz [5], based on a Poisson model for the soliton statistics [1], which yields a theoretical soliton wavenumber spectrum of the form W_{2}(k|0) = A\{1 + (bk)^{2}\}^{-2} . The inferred parameters of the soliton structure are consistent with experimental observations of the acoustic baekscatter [5]. They also suggest the critical role of the near-surface locally turbulent winds. These are inadequately parameterized by mean wind speed ( \bar{U}_{a} ) alone: higher moments (var \bar{U}_{a} , etc.) are needed to account for the often markedly different wave surface states and resulting spectra, backscatter levels, etc., for the unsaturated nltragravity and capillary wavenumber regions (1/2-6 rad. cm{-1} ), which are consistently observed in practice [2], [3], [11], [13]. Finally, it is emphasized that, at this stage, the aim is to demonstrate feasibility and plausibility, not a full proof of the proposed mechanisms.
TL;DR: In this paper, the authors describe how to discover a supplementary experience and achievement by spending more cash, yet when? attain you endure that you require to acquire those every needs in imitation of having significantly cash? Why don't you attempt to acquire something basic in the beginning?
Abstract: Eventually, you will completely discover a supplementary experience and achievement by spending more cash. yet when? attain you endure that you require to acquire those every needs in imitation of having significantly cash? Why don't you attempt to acquire something basic in the beginning? That's something that will guide you to understand even more going on for the globe, experience, some places, bearing in mind history, amusement, and a lot more?
TL;DR: In this article, the authors derived analytic expressions for filters which minimize the power spectrum of the array response to the undesired coherent signal while simultaneously providing an all-pass condition for the desired signal.
Abstract: The response of an array of sensors to coherent undesired noise interfering with the measurement of a desired signal can be optimized if special filters are applied to the outputs of the sensors. In this paper, we derive analytic expressions for filters which minimize the power spectrum of the array response to the undesired coherent signal while simultaneously providing an all-pass condition for the desired signal. These filters are shown to yield an array rejection response which has zero-width main lobes and no sidelobes. An example illustrating the results is also presented.