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OCEANS '98 Conference Proceedings

Date Sept. 28 1998-Oct. 1 1998

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  • OCEANS '98 [front matter]

    Page(s): i - viii
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    Freely Available from IEEE
  • Table of contents

    Page(s): ix - xxxi
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    Freely Available from IEEE
  • Index [of authors]

    Page(s): 0_2 - 0_5
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    Freely Available from IEEE
  • Real-time architecture for cable tracking using texture descriptors

    Page(s): 1496 - 1500 vol.3
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    We present a texture analysis algorithm based on perceptual features. A specific architecture has been developed in order to implement texture features extraction which is low cast, easy-to-implement and reprogrammable depending on the vision system conditions. We apply our algorithm in detection and tracking of submarine cable where underwater vehicles control requires high speed in visual information treatment View full abstract»

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  • The need for conformity in GPS navigation and pilotage systems

    Page(s): 1336 - 1339 vol.3
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    There has been a steady growth in the development of satellite-based vessel tracking systems and electronics aids for pilotage, especially on inland waterways. The Global Positioning System (GPS) is a key element in many of the activities that have been undertaken. The global aspects of the technology, however, do not ensure conformity among emerging systems. It is time to make a concerted effort to realize the international benefits of truly global systems versus the present tendency to implement regional systems. At the present time, significant efforts are underway in the Panama Canal, the Great Lakes/Saint Lawrence Seaway system, and in Central America to modernize maritime systems using GPS satellite technology. System upgrades are not limited to just waterways in the Americas, but rather are taking place on a global scale. The proliferation of advanced radionavigation and pilotage systems is occurring because of demands for more efficient and safer maritime operations. This paper describes and examines some of the current forcing functions that are driving the evolution in marine technology. Another major factor analyzed is the growing trend to tightly couple the requirements of vessel traffic management systems with those of radionavigation systems on-board vessels. The most significant point of contention regarding changes taking place in maritime systems worldwide, particularly those employing automatic identification system (AIS) technology, is the unavailability of international standards. This paper discusses the possibility of establishing some measure of conformity now in the number of GPS based AIS navigation and pilotage systems View full abstract»

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  • On mechanism of wind wave noise generation

    Page(s): 1378 - 1381 vol.3
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    The classification of underwater sound sources requires detailed knowledge of ambient noise structure at different hydrodynamic and meteorological conditions. This includes a better understanding of the mechanism of ambient sound generation and attenuation. It is generally recognised that breaking wind-waves are the dominant source of natural ambient noise in the ocean. The noise intensity is usually characterised by the Knudsen frequency spectra with the typical slope of -5-6 dB/octave. First measurements of the Knudsen spectra revealed strong correlation of the wind speed to underwater ambient noise. Recent studies suggested that the wind is the source of the Knudsen spectra only through the mediation of the spilling breakers, which are the sources of the sound-radiating air bubbles. Calculating the amount of dissipated wave energy that is spent on the bubble entrainment against buoyancy, a conclusion on the bubble cloud parameters can be made. In the paper, a mathematical model of ambient noise generation due to wave breaking is presented. The acoustic energy is generated by the collective oscillation of the bubbles in the bubble cloud, resulting in a much lower eigenfrequency than that of a single bubble. The model leads to an expression for noise intensity spectra due to wind-wave breaking. The model suggests that observed shape of the Knudsen spectra is defined mainly by the structure of bubble population and lowest eigenfrequency of collective bubble oscillation View full abstract»

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  • Methods for evaluating debris on the deep sea floor

    Page(s): 1512 - 1524 vol.3
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    The distribution and abundance of larger marine debris were investigated using four different methods (bottom trawling, pole trawling, videophotography and submersibles) during oceanographic cruises undertaken from November 1993 to July 1998. Different types of debris were enumerated, particularly pieces of plastic, plastic and glass bottles, metallic objects, glass, and various materials including fishing gear. The results were highly variable depending on the methodologies used as well as hydrodynamic, geomorphologic or anthropic factors. Concentrations reached more than 200 pieces of debris per hectare in some areas. In most stations sampled, plastic bags accounted for a very high percentage (more than 90%) of total debris. In the Mediterranean Sea, most debris was found in canyons along the continental slope. The adequacy of each method was considered in terms of qualitative and quantitative analysis. For larger areas, pole trawling was the most suitable method whereas narrow eroded areas such as canyons required submersibles View full abstract»

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  • The limits of spatial resolution achievable using a 30 kHz multibeam sonar: model predictions and field results

    Page(s): 1823 - 1827 vol.3
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    A Simrad EM300 multibeam sonar was used to attempt to resolve small (~5 m high) targets in 450 m of water. The targets had previously been surveyed using a deeply towed 59 kHz sidescan sonar. Using multisector active yaw, pitch and roll compensation, together with dynamically altering angular sectors, the sonar is capable of maintaining sounding densities of as tight as 10 m spacing in these water depths. This is significantly smaller than the largest dimension of the projected beam footprints (16-64 m). The observed data suggest that the targets are intermittently resolved. The field results compare well to the output of a numerical model which reproduces the imaging geometry. Possible variations in the imaging geometry are implemented in the model, comparing equiangular and equidistant beam spacings, differing angular sectors and all the different combinations of transmit and receive beam widths that are available for this model of sonar. While amplitude detection is significantly aliased by targets smaller than the across track beam footprint, under conditions where the signal to noise ratio is favorable, phase detection can be used to reduce the minimum size of target observed to about the scale of the across track beam width. Thus having the beam spacing at the scale is justifiable. The phase distortion due to smaller targets, however, is generally averaged out View full abstract»

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  • Sub-bottom characterisation using a parametric sonar

    Page(s): 1828 - 1832 vol.3
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    High quality seabed data are needed in many situations connected with marine surveillance and monitoring. At FOA we are developing remote sensing methods, which use a parametric sonar. It has a very small footprint, which means that individual small objects can be detected and separated. The sonar can be operated with broadband signals, which gives good resolution in the time domain. We have used a parametric sonar in very shallow water in the Baltic. The results of our interpretation are compared to “ground truth” from bottom samples. We have tested the sonar's capability to detect embedded objects by burying test targets into the ground. The recorded signals are then analysed by various detection algorithms. These give the position of the object. The physical properties are then determined by comparison to theoretical calculations on object signatures View full abstract»

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  • Underwater vehicle synthetic environment demonstration: an overview

    Page(s): 1387 - 1391 vol.3
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    The use of synthetic environments (SE) and network technologies such as the World Wide Web (WWW) enable information from distributed simulations to be integrated, visualised, manipulated and interacted with in near real time in a virtual world. This capability enables underwater system designs and concepts to be comprehensively prototyped, tested, verified and validated in a virtual world before manufacture. These benefits have the potential to reduce overall risks and costs. DERA have been involved in work demonstrating the use of SE in the mine warfare area. An initial demonstration involved the combination of information from UUV 6 degree-of-freedom, seabed terrain, side scan sonar, video and command and control system simulations. This data was combined using the distributed interactive simulation (DIS) protocol to link entity level simulations. A stealth viewer was used to visualise interaction of 3D entity models. The paper discusses the work conducted for this demonstration highlighting the method of implementation, results and likely future work View full abstract»

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  • On control approaches for efficient primary energy conversion in irregular waves

    Page(s): 1427 - 1431 vol.3
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    Active control has been extensively studied in the wave energy literature. Advantages of control include potential improvement in year-round productivity and potential decrease in device size. Control in irregular waves presents special difficulties. This paper summarizes some of the recent work on reactive control in irregular waves. A part of the total actuator force requires estimation of future velocity. Approximate estimates based on past measurements are utilized. Results show considerable performance enhancement in wave spectra dominated by energy-rich swells. For further enhancement, the estimation quality must be improved View full abstract»

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  • Low-speed targets sonar detection using autoregressive models in reverberation; experimental performances for wideband signals

    Page(s): 1285 - 1289 vol.3
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    We generalize here a suboptimal method to detect any kind of wideband signals embedded in the reverberation noise they have created. As this noise is strongly colored, first of all the optimal detector consists in whitening the observation. This step is made very difficult because of the nonstationarity of the reverberation noise. Under local stationarity assumption of the reverberation, we cut the received signal into blocks; On each block, we consider that the noise can be modeled as an AR process. Thus we perform the whitening step and finally an appropriate matched filter is applied. We also discuss the validity of local stationarity for the reverberation using the spectral measure of Itakura. We finally present performances of the approach valuated on two different experimental data sets View full abstract»

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  • Sea trials of the deep scientific system VICTOR 6000

    Page(s): 1573 - 1577 vol.3
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    In 1992, IFREMER decided to develop the deep teleoperated system VICTOR 6000. This system, rated to 6000 metres water depth, is dedicated to scientific research and is able to carry out a large scale optical survey and local inspection. The first at sea trials started in September 1997 for shallow tests close to the IFREMER centre. The tests were then continued on R/V Thalassa in December 1997 for a 3-week cruise where the system proved its ability to dive up to 3500 metres. This paper gives a general description of the system in terms of missions and objectives and presents the results of the trials View full abstract»

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  • Rejecting the disturbances due to the umbilical's traction in ROV's control

    Page(s): 1245 - 1249 vol.3
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    Consider the problem of decoupling the effect of the umbilical's traction from the position of a ROV by means of feedback. The problem is first studied with respect to a linearized model of the ROV. Geometric methods show that exact decoupling is not possible, while approximate decoupling can be achieved by means of high-gain feedbacks. The relations with an H approach to the same problem are discussed and the effectiveness of the design methodology with respect to the nonlinear model is shown by means of simulations View full abstract»

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  • Shallow water predictions and HF radar wave measurements in coastal areas

    Page(s): 1666 - 1670 vol.3
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    This paper presents some initial comparisons between HF radar wave measurements and SWAN shallow water wave model results. The comparisons involve fetch limited wave growth and long fetch wave growth scenarios. These allow a simple visual assessment of the results. The HF radar measurements and SWAN results are comparable, although the former contains some spurious measurements, mainly in the near shore. This suggests that the measurements require stricter or different quality controls View full abstract»

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  • Spatially variant and coherent illumination method for undersea object detection and recognition

    Page(s): 1259 - 1263 vol.3
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    Increased optical range of target detection and recognition is always a problem in the marine environment. The inherent optical properties of light absorption and scattering in water, compounded by suspended particulate matter scattering, limit both radiative and information transfer for image formation. Methods for the formation of images in scattering media generally rely upon temporal or spatial methodologies. Some interesting designs have been developed in an attempt to circumvent or overcome the scattering problem. Time gating is a temporal example of image formation whereby a light source is pulse projected toward a target and the detector is time gated to accept image forming illumination from a specific range. To be successful at eliminating much of the backscatter problem, this method requires range information and loses the simplicity of a continuous light source. Holography is one example of an image formation method requiring specific spatial relationships, i.e. mutual coherence between a reference beam and a signal beam. The coherence allows the formation of an interference pattern that carries the signal information on a “spatial carrier”. In order for the method to be of use, the medium in which the beams are carried must preserve the coherence or phase spatially across the beams and in relation to the reference beam. In water, the distance over which the phase may be preserved is dependent upon many factors, including turbulence induced refractive index variations, thermal gradient structure, and relative motion. If pathlength differences exceed the temporal coherence length of the beam, interference is not obtained and the method breaks down. Generally, the demands of maintaining a spatially coherent beam at optical frequencies is difficult over long range thereby limiting the usefulness of the technique for image formation in turbid media. This paper describes a variation of the spatial interferometric technique that relies upon projected spatial gratings with subsequent detection against a quasi-coherent return signal View full abstract»

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  • Multiple source localization using partitioning: algorithms

    Page(s): 1418 - 1421 vol.3
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    This paper addresses the problem of estimating the number of sources, the directions of narrowband signals and the signals emitted by a number of sources. The proposed solution is based on the reformulation of the problem in a way so that the measurement equation can be expressed as a non-linear function of a vector consisting of the locations as well as the signals emitted by the sources. Simulations illustrate that the proposed method selects the correct dimension of this augmented location vector (i.e. it correctly selects the number of sources) while at the same time successfully identifying the source locations and signals, even for a sufficiently small number of snapshots, Furthermore, the method is adaptive in the sense that it has the ability to track changes in the model structure in real time, successfully. Finally, an interesting feature of the proposed algorithm is its natural decoupled form, which makes it amenable for parallel implementations View full abstract»

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  • Statistical and neural techniques to buried object detection and classification

    Page(s): 1269 - 1273 vol.3
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    Systems able to retrieve objects embedded in the sea bottom are of crucial importance for many different tasks, In this paper, an assessment of different advanced signal processing techniques for object detection classification is proposed, Such an assessment based on real data acquired by a parametric sonar, A detector based on the “classify-before-detect” paradigm has been developed that is well suited to exploit the available statistical and spectral a priori information. In other words, a statistical classifier has been employed to distinguish between two classes (i.e., target presence and target absence) exactly like detectors. Concerning classification, the focus has been placed on the exploitation of the object resonances and a neural network has been designed. As a first step the possibility for the network to be properly trained has been assessed, while as a second step the discrimination capability has been verified. The above methods have been tested with an experimental data set in which the echoes of a steel cylinder were embedded in real reverberation echoes, according to low signal-to-reverberation ratios View full abstract»

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  • Radar/sonar multitarget tracking

    Page(s): 1422 - 1426 vol.3
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    This paper examines optimal joint detection and tracking of multiple targets that move randomly in spatially uncorrelated and correlated Gaussian and non-Gaussian (heavy tail) clutter. We develop an integrated detector/tracker and illustrate its performance with synthetic data View full abstract»

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  • Rain cells over the sea monitored by synthetic aperture and weather radars: a comparison

    Page(s): 1445 - 1448 vol.3
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    Rain showers (rain cells) over the sea can be monitored by active microwave sensors because of two processes: (1) the scattering and attenuation of the microwaves by raindrops in the atmosphere and (2) the modification of the sea surface roughness and thus its radar backscatter cross section by the impact of raindrops and by wind gusts associated with rain cells. The first process is used by ground-based weather radars which measure the power backscattered by raindrops in the atmosphere, from which the rain rate can be derived. A combination of both processes causes signatures of rain cells on synthetic aperture radar (SAR) images of the sea. Such signatures consist of irregularly-shaped bright and dark patches with a diameter of several kilometers, often embedded in almost circular structures. In this study, for the first time SAR images of European marginal seas acquired by the C band SAR aboard the European remote sensing satellites ERS-1 and ERS-2 are compared with concurrent C band weather radar images, which allows to unambiguously attribute signatures on the SAR images to rain cells. The study shows even rain cells with relatively low rain rates (<10 mm/h) can cause signatures in ERS SAR images of the sea. These signatures are predominantly caused by the effect of the rain cells on the sea surface roughness View full abstract»

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  • Dual frequency acoustic classification of seafloor habitat using the QTC VIEW

    Page(s): 1296 - 1300 vol.3
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    A program of single frequency seabed classification using QTC VIEW with two separate frequencies has affirmed the effectiveness of this technology. Adding seabed classification to routine bathymetric surveys constitutes an efficient value-added solution to acquisition of needed baseline data for the enforcement of Marine Protected Area legislation and for fisheries habitat management. A local seabed classification test area was thoroughly groundtruthed with a variety of methods. Integration of the two separate frequencies at an intermediate stage of professing achieved near-optimal classification over varied geology. Dual frequency processing was well correlated with ground truth data View full abstract»

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  • WHOI Cable: time domain numerical modeling of moored and towed oceanographic systems

    Page(s): 1681 - 1685 vol.3
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    A new computer program is described for analyzing the statics and dynamics of oceanographic cable structures. The numerical program, WHOI Cable, features a nonlinear solver that includes the effects of geometric and material nonlinearities, bending stiffness for seamless modeling of slack cables, and a model for the interaction of cable segments with the seafloor. The program solves surface and subsurface single-point mooring problems, systems with multiple anchored ends, and towing and drifter problems. Forcing includes waves, current, wind, ship speed, and pay-out of cable. The programs that make-up WHOI Cable run under Unix, DOS, and Windows. There is a familiar Windows-style interface available for Windows 95 and Windows NT platforms. The mathematical framework, numerical algorithm, and interface for WHOI Cable are described and example applications from design and validation studies are presented View full abstract»

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  • Using ambient noise sonar (ANS) to probe the ocean environment in shallow water

    Page(s): 1368 - 1372 vol.3
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    The Ambient Noise Sonar system (ANS) is a passive sonar array that has been developed to study the ocean environment in coastal waters by measuring ocean noise global directivity using only six transducers in a sparse volume array of maximum size 2 m. The array output gives 3D images with thousands of independent pixels for any chosen look direction and so can provide both horizontal and vertical directivity patterns. This system uses the natural broadband characteristics of ambient noise using a multiplicative processing of the cross-correlations between the receivers, similar to Class I T.A.P. arrays. The sonar has already been used in a variety of experiments to probe the ocean environment in shallow waters off the coast of Florida. Although there have been many measurements made of ambient noise levels in shallow water there appear to be very few published results of the ambient noise horizontal directivity. More recently there have been a number of experiments on near-shore ambient noise and these have shown the importance of biological activity in low sea states and breaking waves in high sea states. The results found with the ANS indicate that in tropical waters and in low sea states the noise is highly anisotropic and is generated by biological noise sources and not breaking waves, contrary to the standard assumption that the noise is surface generated and isotropic. Colonies of snapping shrimp have been localized along the coast, clustered around man-made structures and natural reefs. Finally, by monitoring local boat traffic, the ANS used boat noise as a source of opportunity to probe the environment and obtain an estimate of the bottom reflection coefficient View full abstract»

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  • Classification of buried objects using a parametric sonar

    Page(s): 1264 - 1268 vol.3
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    Underwater object identification has been of great interest to acousticians (detection of boulders), marines (detection of buried mines), or archaeologists (detection of wreckage). Image and signal processing succeeds in identifying objects lying on the sea bottom, however identification of an object buried in sediment remains complex. The goal of this work is to obtain a complete identification and localization of objects embedded in sediment using adapted technology. The parametric source, whose properties are based on the nonlinear propagation characteristics of water, has many advantages as an acoustic source (high relative bandwidth, narrow beam) which are useful for object detection and classification View full abstract»

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  • Visual navigation of an autonomous underwater vehicle using image sequences of a scanning sonar

    Page(s): 1833 - 1837 vol.3
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    We use image sequences generated by an electronic scanning sonar to achieve the aim of obstacle avoidance and visual navigation for an autonomous underwater vehicle (AUV). Using sonar systems for the sensing of unknown underwater environments is the best selection in practice. However, the critical demand for real-time signal processing and the uncertainties of AUV's dynamics make online detection of obstacles a challenging task. We use the track-before-detect algorithm to extract information contained in image sequences to estimate the dynamics of the AUV and to solve the problem of detection. This method reduces the computational cost to meet the real-time demand on obstacle avoidance and navigation of the AUV View full abstract»

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