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Oceanic Engineering, IEEE Journal of

Issue 4 • Date Oct. 2003

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Displaying Results 1 - 18 of 18
  • Guest editorial special issue on underwater image and video processing

    Page(s): 569
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    Freely Available from IEEE
  • Author index

    Page(s): 766 - 769
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    Freely Available from IEEE
  • Subject index

    Page(s): 769 - 776
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    Freely Available from IEEE
  • Image processing of underwater multispectral imagery

    Page(s): 583 - 594
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1233 KB) |  | HTML iconHTML  

    Capturing in situ fluorescence images of marine organisms presents many technical challenges. The effects of the medium, as well as the particles and organisms within it, are intermixed with the desired signal. Methods for extracting and preparing the imagery for analysis are discussed in reference to a novel underwater imaging system called the low-light-level underwater multispectral imaging system (LUMIS). The instrument supports both uni- and multispectral collections, each of which is discussed in the context of an experimental application. In unispectral mode, LUMIS was used to investigate the spatial distribution of phytoplankton. A thin sheet of laser light (532 nm) induced chlorophyll fluorescence in the phytoplankton, which was recorded by LUMIS. Inhomogeneities in the light sheet led to the development of a beam-pattern-correction algorithm. Separating individual phytoplankton cells from a weak background fluorescence field required a two-step procedure consisting of edge detection followed by a series of binary morphological operations. In multispectral mode, LUMIS was used to investigate the bio-assay potential of fluorescent pigments in corals. Problems with the commercial optical-splitting device produced nonlinear distortions in the imagery. A tessellation algorithm, including an automated tie-point-selection procedure, was developed to correct the distortions. Only pixels corresponding to coral polyps were of interest for further analysis. Extraction of these pixels was performed by a dynamic global-thresholding algorithm. View full abstract»

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  • Radiative transfer modeling and analysis of spatially variant and coherent illumination for undersea object detection

    Page(s): 570 - 582
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2303 KB) |  | HTML iconHTML  

    Increasing the optical range of target detection and recognition continues to be an area of great interest in the ocean environment. Light attenuation limits radiative and information transfer for image formation in water. In this paper, the authors briefly review current methods of imaging and then describe a variation of the spatial interferometric technique that relies upon projected spatial gratings with subsequent detection against a coherent return signal for the purpose of noise reduction and image enhancement. A model is developed that simulates the projected structured illumination through turbid water to a target and its return to a detector. The model shows an unstructured backscatter superimposed upon a structured return signal. The model has been extended to predict what a camera would actually see, so that various noise-reduction schemes can be modeled. Finally, some water-tank tests are presented, validating original hypothesis and model predictions. The method is advantageous in not requiring temporal synchronization between reference and signal beams and may use a continuous illumination source. Spatial coherency of the beam allows for the detection of the direct return, while scattered light appears as a noncoherent noise term. View full abstract»

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  • Image projection and composition with a front-scan sonar system: methods and experimental results

    Page(s): 687 - 698
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    This paper describes a complete set of methods for arranging acoustic images of the sea floor by projecting and interpolating data gathered with a novel front-scan sonar system, developed in the context of the EC-COSMOS project. Traditional sonar imaging systems for sea-floor analysis generate acoustic images during the motion of a ship; on the contrary, the front-scan sonar system not only provides information unreachable by traditional devices (blind region), but also does not need the ship motion to compose a whole image of the sea floor. Two different projection methods have been devised: a simpler analytical solution and a more precise ray-tracing approach. The development of an analytical solution is possible under the classical assumptions about a flat sea floor and a constant sound velocity profile; when these hypotheses are not realistic or a more precise image is required, a numerical solution obtained by a ray-tracing approach can be applied, which is based on some ad hoc solutions worked out for the front-scan sonar system. To move from the projection results to an image defined over a dense matrix of pixels, an interpolation stage is needed. To this end, an algorithm based on the generation of virtual-beam signals (only where necessary) has been tested and compared with more-traditional techniques. The potentials of the proposed projection and interpolation methods have been evaluated and some comparisons have been made, using real data gathered with the COSMOS sonar prototype during trials at sea. View full abstract»

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  • An integrated sensory-intelligent system for underwater acoustic signal-processing applications

    Page(s): 750 - 759
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (578 KB) |  | HTML iconHTML  

    A generic integrated sensory-intelligent system (ISIS) is developed for underwater acoustic signal-processing applications. ISIS constantly monitors the current acoustic channel conditions and smoothly integrates the outputs of the most appropriate signal-processing procedures or algorithms available to it for those conditions. The system is based on a generalization of a tuneable approximate piecewise linear (TAPL) model derived from the modified probabilistic neural network (MPNN). This model was designed to seamlessly integrate a set of local linear signal-processing algorithms within a given multidimensional data space. Depending on the input signal distortions, which are determined by environmental effects, ISIS automatically weighs and adds the outputs from a set of processing algorithms working in parallel. The weighting is related to the "closeness" of each algorithm to the sensed input signal characteristics or some other measured environmental state. A single tuning parameter is used to smoothly and seamlessly select appropriately among the parallel processing algorithm outputs. A very small tuning-parameter value selects the closest most appropriate algorithm output. At the other extreme, a fixed weighted average of all the algorithm outputs is produced with a very large value. Otherwise, a dynamic weighed average of all algorithm outputs is achieved with values in between. Some features and benefits of ISIS are demonstrated with an illustrative linear sweep chirp signal-detector estimation problem characterized by extremely variable Doppler conditions. View full abstract»

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  • Transient discrimination using a subspace method [acoustic array signal processing]

    Page(s): 763 - 765
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (237 KB) |  | HTML iconHTML  

    This paper describes a method using a subspace algorithm that can be used to discriminate between signals. Discrimination is necessary to ensure that the same transient from different data records is used in processing. The subspace discrimination algorithm was tested against synthetic transients and found to discriminate well at high signal-to-noise ratios (SNRs). View full abstract»

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  • Flattening the side-lobes of wide-band beam patterns [acoustic arrays]

    Page(s): 760 - 762
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    Recently, simulated annealing has been proposed as a suitable method for optimizing the weighting window of a linear array working under wide-band conditions. This paper introduces and discusses a new energy function that, minimized by simulated annealing, produces a beam pattern showing a flat side-lobe profile over a large interval. View full abstract»

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  • Toward large-area mosaicing for underwater scientific applications

    Page(s): 651 - 672
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    Severe attenuation and backscatter of light fundamentally limits our ability to image extended underwater scenes. Generating a composite view or mosaic from multiple overlapping images is usually the most practical and flexible way around this limitation. In this paper, we look at the general constraints associated with imaging from underwater vehicles for scientific applications - low overlap, nonuniform lighting, and unstructured motion $and present a methodology for dealing with these constraints toward a solution of the problem of large-area global mosaicing. Our approach assumes that the extended scene is planar and determines the homographies for each image by estimating and compensating for radial distortion, topology estimation through feature-based pairwise image registration using a multiscale Harris interest point detector coupled with a feature descriptor based on Zernike moments, and global registration across all images based on the initial registration derived from the pairwise estimates. This approach is purely image based and does not assume that navigation data is available. We demonstrate the utility of our techniques using real data obtained using the Jason remotely operated vehicle (ROV) at an archaeological site covering hundreds of square meters. View full abstract»

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  • Wave synchronizing crane control during water entry in offshore moonpool operations - experimental results

    Page(s): 720 - 728
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (713 KB) |  | HTML iconHTML  

    A new strategy for active control in heavy-lift offshore crane operations is suggested by introducing a new concept referred to as wave synchronization. Wave synchronization reduces the hydrodynamic forces by minimizing variations in the relative vertical velocity between payload and water using a wave-amplitude measurement. Wave synchronization is combined with conventional active heave compensation to obtain accurate control. Experimental results using a scale model of a semi-submerged vessel with a moonpool shows that wave synchronization leads to significant improvements in performance. Depending on the sea state and payload, the results indicate that the reduction in the standard deviation of the wire tension may be up to 50%. View full abstract»

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  • High-frequency bistatic sea-floor scattering from sandy ripple bottom

    Page(s): 711 - 719
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    To obtain the bistatic scattering function on the sandy ripple bottom, high-frequency bistatic sea-floor scattering measurements were made in the shallow waters off the east coast of Korea. A sand ripple field was present at the site, with wavelength generally in the 10-20-cm range. The mean ripple orientation relative to the direction of wave propagation was estimated to be roughly 20°-30°. Field experiments were made to measure forward (in-plane) and out-of-plane scattering from the ripple bottom. The measured scattering strengths were compared to the predictions of the APL-UW bistatic scattering model. Overall, forward-scattering strength measurements showed favorable comparison with the model predictions. The global scattering characteristics for the ripple bottom gave an augmented out-of-plane scattering. View full abstract»

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  • Mosaic-based navigation for autonomous underwater vehicles

    Page(s): 609 - 624
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    We propose an approach for vision-based navigation of underwater robots that relies on the use of video mosaics of the sea bottom as environmental representations for navigation. We present a methodology for building high-quality video mosaics of the sea bottom in a fully automatic manner, which ensures global spatial coherency. During navigation, a set of efficient visual routines are used for the fast and accurate localization of the underwater vehicle with respect to the mosaic. These visual routines were developed taking into account the operating requirements of real-time position sensing, error bounding, and computational load. A visual servoing controller, based on the vehicle's kinematics, is used to drive the vehicle along a computed trajectory, specified in the mosaic, while maintaining constant altitude. The trajectory toward a goal point is generated online to avoid undefined areas in the mosaic. We have conducted a large set of sea trials, under realistic operating conditions. This paper demonstrates that without resorting to additional sensors, visual information can be used to create environment representations of the sea bottom (mosaics) and support long runs of navigation in a robust manner. View full abstract»

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  • Automatic indexing of underwater survey video: algorithm and benchmarking method

    Page(s): 673 - 686
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1245 KB) |  | HTML iconHTML  

    It is often the case that only a few sparse sequences of long videos from scientific underwater surveys actually contain important information for the expert. Locating such sequences is time consuming and tedious. A system that automatically detects those critical parts, online or during post-mission tape analysis, would alleviate the expert workload and improve data exploitation. In this paper, a methodology for evaluating the performance of such a system on real data is presented. Interesting sequences are started by changes of visual context. An algorithm to detect significant context changes in benthic videos in real time has been presented by Lebart et al. in 2000. It is used as an illustration for this methodology - its performance is studied and benchmarked on real underwater data, ground truthed by an expert biologist. Various issues relating to the complexity of the problems of automatically analyzing underwater video are also discussed. View full abstract»

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  • Characteristics of acoustic propagation to the eastern vertical line array receiver during the summer 1996 New England shelfbreak PRIMER experiment

    Page(s): 729 - 749
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    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. View full abstract»

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  • Quantitative visualization of geophysical flows using low-cost oblique digital time-lapse imaging

    Page(s): 699 - 710
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    Estuaries and coastal waters are regions where many different important physical processes can be found. Although the physical scale of these processes is often relatively small, their time scales are correspondingly rapid and aliasing is usually a problem in sampling programs. There can be significant spatial variations in mixing and flow patterns, which are usually learned only through long experience in a particular region. Observational and interpretation difficulties might be significantly simplified with a simple remote sensing tool to be used in conjunction with standard techniques. Here, the use of digital time-lapse photography at highly oblique angles as a tool for flow visualization is discussed. The interaction of surface waves with slicks and internal motions can cause apparent changes in the shade and color of water at shallow angles in a way not apparent in downlooking views. The use of time-lapse techniques allows us to isolate time scales of interest and, by "speeding up" low-frequency motions, causes them to become more apparent to the eye. A cheap and portable system based on commercially available equipment is described and various advantages and shortcomings are discussed. Results are shown to illustrate the utility of the observational system. View full abstract»

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  • Segmentation methods for visual tracking of deep-ocean jellyfish using a conventional camera

    Page(s): 595 - 608
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    This paper presents a vision algorithm that enables automated jellyfish tracking using remotely operated vehicles (ROVs) or autonomous underwater vehicles (AUVs). The discussion focuses on algorithm design. The introduction provides a novel performance-assessment tool, called segmentation efficiency, which aids in matching potential vision algorithms to the jelly-tracking task. This general-purpose tool evaluates the inherent applicability of various algorithms to particular tracking applications. This tool is applied to the problem of tracking transparent jellyfish under uneven time-varying illumination in particle-filled scenes. The result is the selection of a fixed-gradient threshold-based vision algorithm. This approach, implemented as part of a pilot aid for the Monterey Bay Aquarium Research Institute's ROV Ventana, has demonstrated automated jelly tracking for as long as 89 min. View full abstract»

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  • Stereovision imaging on submersible platforms for 3-D mapping of benthic habitats and sea-floor structures

    Page(s): 625 - 650
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    We investigate the deployment of a submersible platform with stereovision imaging capability for three-dimensional (3D) mapping of benthic habitats and other sea-floor structures over local areas. A complete framework is studied, comprising: 1) suitable trajectories to be executed for data collection; 2) data processing for positioning and trajectory followed by online frame-to-frame and frame-to-mosaic registration of images, as well as recursive global realignment of positions along the path; and 3) 3D mapping by the fusion of various visual cues, including motion and stereo within a Kalman filter. The computational requirements of the system are evaluated, formalizing how processing may be achieved in real time. The proposed scenario is simulated for testing with known ground truth to assess the system performance, to quantify various errors, and to identify how performance may be improved. Experiments with underwater images are also presented to verify the performance of various components and the overall scheme. View full abstract»

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Aims & Scope

The IEEE Journal of Oceanic Engineering (ISSN 0364-9059) is published quarterly by the IEEE Oceanic Engineering Society (IEEE OES). The scope of the Journal is the field of interest of the IEEE OES, which encompasses all aspects of science, engineering, and technology that address research, development, and operations pertaining to all bodies of water. This includes the creation of new capabilities and technologies from concept design through prototypes, testing, and operational systems to sense, explore, understand, develop, use, and responsibly manage natural resources.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
N. Ross Chapman
School of Earth & Ocean Sciences
University of Victoria
3800 Finnerty Road
Victoria, BC V8P 5C2 Canada
chapman@uvic.ca