IEEE Oceans Research Articles

IEEE Oceanic Engineering Society WIE Panels: Oceans of Opportunities

IEEE Oceanic Engineering Society WIE Panels: Oceans of Opportunities

Design of performance-weighted blended mode filters for underwater experiments

Normal mode signals are valuable in ocean acoustic tomography and source localization, assuming that they can be separated using spatial or temporal filtering. Common spatial mode filters include the matched filter (MF) [Ferris, JASA, 1972] and the pseudo-inverse (PI) filter [Tindle et al., JASA, 1978]. Choosing a filter and its parameters, e.g., the PI filter rank, requires knowledge that is not readily available. For instance, it is unlikely that the levels of ambient noise or interference from other modes is known a priori. To address this problem, Chakrabarti and Wage [IEEE Oceans, 2021, 2022] developed a Performance-Weighted Blended mode filtering algorithm that adapts quickly to changing conditions and achieves better performance than a single fixed mode filter. The PWB filter blends a set of PI filters of varying ranks, including a rank-1 PI filter (MF). A PI filter can suppress interference from neighboring modes but is more vulnerable to noise than the MF, which has the maximum white noise gain. This talk explores practical aspects of the PWB implementation, including how to select the set of filters to blend given realistic underwater noise conditions. We will show experimental and simulated data to illustrate performance in different environments. [Work supported by ONR.]

Frequency-wavenumber spectrum estimation using blended dominant mode rejection beamforming

Capon [Proc. IEEE (1969)] designed the minimum variance distortionless response (MVDR) beamformer to obtain spectral estimates with better resolution than the conventional averaged-periodogram estimator. The MVDR spectrum is a function of the inverse of the sample covariance matrix (SCM), which often must be regularized prior to inversion. To address conditioning problems, Abraham and Owsley [IEEE Oceans (1990)] developed a modified MVDR approach called dominant mode rejection (DMR). The DMR beamformer defines its weights using a structured covariance consisting of a low-rank interference subspace plus an orthogonal noise subspace. It assumes the rank of the interference is known. Recently, Buck and Singer [IEEE SAM (2018)] proposed the blended DMR beamformer that eliminates the need for rank estimation by defining a weight vector that is an affine combination of fixed-rank DMR beamformers. This talk investigates frequency-wavenumber estimation using blended DMR, focusing particularly on efficient implementations for large linear arrays. Adapting the approach described by Therrien [Prentice Hall (1992)] for MVDR, the blended DMR spectrum for an equally spaced array can be computed using fast Fourier transforms of the sample eigenvectors. Results will be illustrated using experimental data from underwater vertical arrays. [Work supported by ONR.]

Editorial Outreach, Impact, and Earthzine

Discusses the need for the OES to launch various outreach programs to promote the industry and encourage interest in the field of oceanic engineering. Outreach can be undertaken in many ways. Authors could offer public talks on thework done, conduct laboratory visits,write blog articles about interesting research findings, publish short videos illustrating key ideas, organize nonspecialist workshops and events, or even publish popular science magazine articles or books. Talks, workshops, and similar events are excellent for personal engagement, but the number of people that they reach is typically small. The impact created is limited. On the other hand, popular science magazine articles, books, blog articles, and online videos reach a much larger audience. One outreach avenue for authors to consider is Earthzine, a magazine of the IEEE Oceanic Engineering Society. Earthzine aims to provide up-to-date information on science and technology related to Earth observation, with the hope to educate and inspire. It accepts short-to-medium length articles for publishing, with a simple editorial process for quality control and improved readability.

Guest Editorial Pushing for Higher Autonomy and Cooperative Behaviors in Maritime Robotics

The papers in this special section examine the technology of maritime robotics. These papers are the result of a collaborative effort between the IEEE Oceanic Engineering Society, the U.S. Office of Naval Research (ONR), and RoboNation, a nonprofit robotics organization formerly known as AUVSI foundation. The field of maritime robotics is swiftly moving toward integration of air, surface, and subsurface autonomous systems. For example, where autonomous maritime systems (AMS) are composed of heterogeneous assets, surface vehicles are now often capable of transporting aerial and underwater vehicles, leveraging the benefits of each to increase mission endurance and capabilities. In seeking to integrate land, sea, and air vehicle systems, it is natural to look toward leveraging advances made separately in each domain. For example, substantial similarities exist between the desired behavioral capabilities of autonomous land vehicles and those of autonomous marine systems. Recent advances in the field of driverless cars may therefore be applicable to autonomous surface vessels, underwater vehicles, and even aerial vehicles.

Guest Editorial Cutting edge autonomous underwater vehicle technology

This special issue focuses on the rapidly evolving technologies on autonomous underwater vehicles (AUVs). AUVs are now widely used in the world as a useful tool to explore underwater environments. We would like to share an overview of the latest state of the AUV technologies and applications, and evoke discussions on current challenges and future developments. The special issue features invited prominent papers from the Joint Symposium/Workshop 2016 IEEE OES Autonomous Underwater Vehicle (AUV 2016), which was held in November 2016 at the University of Tokyo, Japan. It is a biannual workshop organized by the IEEE Oceanic Engineering Society (OES). This event has now become a well-established and prestigious international gathering of some of the best in the field. This time, the workshop was held in Asia for the first time. In total, 73 papers were presented, attracting 133 participants from 20 countries. The workshop covers all topics relevant to AUVs, from component technologies to operation, in single-track sessions providing opportunities for the researchers and engineers to discuss the relevant technologies in detail. Today, as AUVs become commercially available and operated around the world, we believe the workshop should address not only the technology to develop a new AUV, but also cover more extensive interests related to AUVs - from the know how obtained through operation to the data collected by AUVs. We tried to incorporate this idea into the program. The special issue papers are briefly summarized.

Reversible quasi-holographic line-scan processing for acoustic imaging and feature isolation of transient scattering

Transient acoustic scattering data from objects obtained using a one-dimensional line scan or two-dimensional raster scan can be processed via a linear quasi-holographic method [K. Baik, C. Dudley, and P. L. Marston, J. Acoust. Soc. Am. 130, 3838–3851 (2011)] in a way that is reversible, allowing isolation of spatially or temporally dependent features [T. M. Marston et al., in Proc. IEEE Oceans 2010]. Unlike nearfield holography the subsonic wavenumber components are suppressed in the processing. Backscattering data collected from a collocated source/receiver (monostatic scattering) and scattering involving a stationary source and mobile receiver (bistatic) may be processed in this manner. Distinct image features such as those due to edge diffraction, specular reflection, and elastic effects may be extracted in the image domain and then reverse processed to allow examination of those features in time and spectral domains. Multiple objects may also be isolated in this manner and clutter may be removed [D. J. Zartman, D. S. Plotnick, T. M. Marston, and P. L. Marston, Proceedings of Meetings on Acoustics 19, 055011 (2013) http://dx.doi.org/10.1121/1.4800881]. Experimental examples comparing extracted features with physical models will be discussed and demonstrations of signal enhancement in an at sea experiment, TREX13, will be shown. [Work supported by ONR.]

Fast nearfield to farfield conversion for circular synthetic aperture sonar

Monostatic circular synthetic aperture sonar (CSAS) images are formed by processing azimuthal angle dependent backscattering from a target at a fixed distance from a collocated source/receiver. In the laboratory data is taken by fixing the source location and spinning the target via a rotating mount. Typical CSAS imaging algorithms [Marston et al., Proc. IEEE Oceans (2011); Ferguson et al., J. Acoust. Soc. Am. 117, 2915 (2005)] assume the scattering data are taken in the farfield. Experimental constraints may make farfield measurements impractical and thus require a target to be scanned in the nearfield. If left uncorrected, this results in distortions of the target image and possible distortions of the angular dependence of features. A fast approximate Hankel function based algorithm is presented that converts nearfield data to farfield data. Images and spectrograms of an extended target are compared for both cases. Spatial sampling requirements for data collection are also considered. [Work supported by ONR.]

Reversible quasi-holographic line-scan and circular aperture processing for acoustic imaging and feature isolation

One-dimensional line scans of objects by a collocated source/receiver can be processed via a linear quasi-holographic method [Baik et al., J. Acoustic Soc. Am. 130, 3838–3851 (2011)] to produce an image in a way that is reversible for signal isolation. Distinct image features such as those due to edge diffraction, specular reflection, or elastic effects can then be extracted in the image domain. Images are then reverse processed to allow examination of the isolated features in time and spectral domains and removal of clutter [Zartman et al., Proceedings of Meetings on Acoustics (POMA) (June, 2013), Vol. 19, p. 055011]. In related research monostatic data from a circular synthetic aperture may be reversibly processed in a way favorable for feature extraction [Marston et al., Proc. IEEE Oceans 2011 (2011)]. Experimental examples comparing extracted features with physical models will be discussed. [Work supported by ONR.]

Buried object imaging using reflection tomography

A recent pioneering study of Steven Schock provided high-quality imaging of buried objects using the buried object sensing sonar (BOSS) system in a towed or AUV-mounted configuration [Schock, Proc. IEEE Oceans, 2005]. This paper numerically investigates the performance of compressive sensing (CS) and standard backprojection methods for imaging multiple buried objects using a sonar system similar to the BOSS. Synthetic data are generated using a 3-D pseudo-spectral model for different sediment types and geometries including synthetic aperture sonar. As compared to the standard backprojection methods, the CS-based reflection tomography provided sharper images of buried objects using smaller data sets. Based on the CS performance, several improvements on the BOSS system and data collection schemes are also presented. [Work supported by ONR.]

Effect of scattering albedo on attenuation and polarization of light underwater

Recent work on underwater laser communication links uses polarization discrimination to improve system performance [Appl. Opt.48, 328 (2009)] [in Proceedings of IEEE Oceans 2009 (IEEE, 2009), pp. 1-4]. In the laboratory, Maalox antacid is commonly used as a scattering agent. While its scattering function closely mimics that of natural seawaters, its scattering albedo can be much higher, as Maalox particles tend to be less absorbing. We present a series of experiments where Nigrosin dye is added to Maalox in order to more accurately recreate real-world absorption and scattering properties. We consider the effect that scattering albedo has on received power and the degree of depolarization of forward-scattered light in the context of underwater laser communication links.

Acoustic modeshape inversion using deep water ambient noise measurements

Assuming that ambient noise can be represented by a sum of uncorrelated acoustic modes, the eigenvectors of the noise covariance matrix for a vertical line array should correspond to the sampled modeshapes. In previous work several authors have investigated using an eigendecomposition of the noise covariance to estimate the mode functions in shallow water, e.g., Wolf et al. [Proc. of the 1993 IEEE Oceans Conf.,vol. I, pp. 99‐104], Hursky et al. [J. Acoust. Soc. Am., 109(4), pp. 1355‐1366], and Nielsen and Westwood [J. Acoust. Soc. Am., 111(2), pp. 748‐756]. While the same approach should work for deep water scenarios, only few deep water experiments have deployed arrays with sufficient aperture to resolve the modes, e.g., the work D'Spain et al. [Pure appl. geophys., Vol. 158, pp. 475‐512]. This paper explores the problem of inverting for the acoustic modes of a deep water waveguide using ambient noise measurements. In particular the paper focuses on important signal processing issues, including data snapshot requirements, and the effects of array tilt. Data from a deep water propagation experiment will be used to quantify how well the empirical modes match the true modes derived from measured environmental data. [Work supported by an ONR Young Investigator Award.]

The IEEE Oceanic Engineering Society at Forty: The Challenges of an Evolving Society

The IEEE oceanic engineering society (OES) has completed forty years of active engagement: the initial eight years in the form of the oceanography coordinating committee (OCC), followed by seven years as the council of oceanic engineering (COE), then the past twenty-five years in the form of an IEEE society. During those forty years, the OCC/COE/OES has existed to serve society, the profession, the oceanic engineering community, and the professional interests of IEEE members working in oceanic engineering. OES has sponsored a strong set of conferences, including OCEANS, the offshore technology conference (OTC), the Undersea Technology (UT) symposium, the United States/European Union (U.S/EU) Baltic International Symposium series, and a variety of specialty workshops. The OES publishes an influential group of science and technology publications, including its flagship IEEE JOURNAL OF OCEANIC ENGINEERING (JOE), a quarterly newsletter, and a "just-in-time" electronic newsletter. The OES has sought to encourage engineering students to enter the oceanic engineering field through a variety of student-focused activities, including the OCEANS conference student-posters program, human-powered submarine races, the Ocean Science Bowl competitions, and an academic scholarship. Chapters have been established in eight IEEE global regions of the world. These forums and activities have been established and maintained to allow OES members and others in the oceanic engineering community to learn and grow by interacting with each other and sharing their ideas and contributions for solution to technical problems and to the broader challenges of society. As the society has moved through its various eras described later, the OES has invented ways to serve its members and the community at-large and will continue to adapt, innovate, modify, and otherwise support the changing needs of the profession.

Objective sampling with EAGLE to improve acoustic prediction accuracy

Some Navy operations require extensive acoustic calculations. The standard computational approach is to calculate on a regular grid of points and radials. In complex environmental areas, this implies a dense grid and many radials (i.e., long run times) to achieve acceptable accuracy and detail. However, Navy tactical decision aid calculations must be timely and exhibit adequate accuracy or the results may be too old or too imprecise to be valuable. This dilemma led to a new concept, OGRES (Objective Grid/Radials using Environmentally-sensitive Selection), which produces irregular acoustic grids [Rike and DelBalzo, Proc. IEEE Oceans (2002)]. Its premise is that physical environmental complexity controls the need for dense sampling in space and azimuth, and that transmission loss already computed for nearby coordinates on previous iterations can be used to predict that complexity. Recent work in this area to further increase accuracy and efficiency by using better metrics and interpolation routines has led to the Efficient Acoustic Gridder for Littoral Environments (EAGLE). On each iteration, EAGLE produces an acoustic field for the entire area of interest with ever-increasing resolution and accuracy. An example is presented where approximately an order of magnitude efficiency improvement (over regular grids) is demonstrated. [Work sponsored by ONR.]

Optimal temperature sampling with SPOTS to improve acoustic predictions

The Modular Ocean Data Assimilation System (MODAS) uses optimal interpolation to assimilate data (e.g., XBTs), and to create temperature nowcasts and associated uncertainties. When XBTs are dropped in a uniform grid (during surveys) or in random patterns and spaced according to resources available their assimilation can lead to nowcast errors in complex, littoral regions, especially when only a few measurements are available. To mitigate, Sensor Placement for Optimal Temperature Sampling (SPOTS) [Rike and DelBalzo, Proc. IEEE Oceans (2003)] was developed to rapidly optimize placement of a few XBTs and to maximize MODAS accuracy. This work involves high-density, in situ data assimilation into MODAS to create a ground-truth temperature field from which a ground-truth transmission loss field was computed. Optimal XBT location sets were chosen by SPOTS, based on original MODAS uncertainties, and additional sets were chosen, based on subjective choices by an oceanographer. For each XBT set, a MODAS temperature nowcast and associated transmission losses were computed. This work discusses the relationship between temperature uncertainty, temperature error, and acoustic error for the objective SPOTS approach and the subjective oceanographer approach. The SPOTS approach allowed significantly more accurate acoustic calculations, especially when few XBTS were used. [Work sponsored by NAVAIR.]

Sparse acoustic gridding in an azimuthally complex environment

A very sparse acoustic gridding method, the Objective Grid/Radials using Environmentally sensitive Selection (OGRES) algorithm, for sonar system performance predictions was reported for a realistic synthetic square annular ridge environment [E. R. Rike and D. R. DelBalzo, Proc. 6th ECUA (2002)] and a complex real-world environment in the Sea of Japan [E. R. Rike and D. R. DelBalzo, Proc. IEEE Oceans (2002)]. The sparse OGRES grids significantly outperformed uniform grids (matched for calculation time) in accuracy. Both cases were based on ground-truth uniform grids high in spatial density, but moderate-to-low in azimuthal density. The present study is a very sparse gridding of a realistic synthetic spiral ridge based on a ground-truth uniform grid high in both spatial and azimuthal density. This analysis extends the previous work by exploring the relationship between the spatial curvature of bathymetric features and optimal azimuthal grid density. The trade-offs between calculation time and accuracy of sonar system predictions for both very sparse and uniform grids are discussed. [Work supported by ONR/NRL under PE 62435N.]

Channel characterization using FSK wave forms

Automatic characterization of underwater acoustic communication channels can support connectivity over a wide range of operational ocean environments. With quantitative measures of the prevailing channel, adaptive modems may optimize the modulation and initialize the demodulation equalizer. A novel channel-estimation technique involving noncoherent processing of received FSK wave forms has been described recently by Green and Rice (Proc. IEEE Oceans’98) and Rice and Green (Proc. MTS Ocean Community Conference, 1998). This technique uses received handshake signals to measure temporal and spectral spreading and signal excess directly, and to estimate coherence parameters. This effort will focus on applying this channel-estimation technique to received and autonomously recorded 8–13 kHz MFSK signals using shallow horizontal channels. [Work supported by ONR 32 and SPAWARSYSCEN.]

A hybrid ray and parabolic equation simulator

The model used here is a hybrid model. It consists of two basic parts. Standard ray theory method [A. Zielinski and X. Gen, IEEE Oceans’94, III, 184–189] used in high frequencies and finite difference parabolic equations [D. Huang, J. Acoust. Soc. Am. 84, 1405–1413 (1988)] used in lower frequencies for the shallow water cases. In both high frequency and low frequency cases the acoustic wave propagation simulator can be used for range-dependent environments. The simulator is highly user friendly. Thus a nonprofessional user is able to work with it easily. For the user, inputs are speed and bottom profiles, source level, beam pattern, and depth and environmental data. Outputs are pressure phase and amplitude in each point of underwater and bottom media. For checking correctness of the results, they were compared with various available benchmarks and they seemed to be quite acceptable. The implementation is to run on PCs under DOS operating systems.

Performance evaluation of horizontal and vertical vector sensor arrays in shallow water environments

In planning an experiment it is essential to have as diverse information as possible in order to obtain a good estimate of the relevant parameters. Traditionally, the inversion for waveguide parameters as well as the source location is done exclusively using pressure measurements. Recently, it has been suggested by Nehorai and Paldi [IEEE Trans. Signal Process. 42, 2481–2491 (1994)] that arrays of vector sensors (sensors that measure both pressure and velocities) could be used. Experiments have also been conducted in deep water by D’Spain et al. [IEEE Oceans (1992)]. In a realistic shallow-water environment the use of either vector or pressure sensors on a linear horizontal/vertical array with amplitude-only or complex-valued data at a number of discrete frequencies are discussed. Based on developed maximum-likelihood functions, the performance for the above type of data will be classified using either a global or a deterministic approach. For the deterministic approach, the Cramer Rao lower bound (CRLB), based on derivatives of the likelihood function, is used. For the global approach the a posteriori distributions are examined. These are based on Monte Carlo integration of the likelihood function. [Work supported by DSO National Laboratories, Singapore.]

A finite element solution of the inverse scattering problem for determining acoustic bubble spectra

The determination of acoustic bubble spectra in the ocean from multi‐frequency attenuation measurements was improved by numerical solution of the inverse scattering problem [K. W. Commander and E. Mortiz, in Proceedings of IEEE Oceans '89, 1181–1185 (1989)]. Although this numerical solution offers an improvement over the resonance approximation (at small radii), it too suffers a loss of accuracy at the small radii end of the bubble spectrum. The numerical solution of this problem has been improved by replacing the Fourier series approximation to the unknown distribution by a piecewise linear polynomial constructed from a series of basis functions. The basis functions used were linear B‐splines or “hat” functions. The resulting coefficient matrices are much less ill‐conditioned than those from the previous method because of the local support of the basis functions. This improvement leads to a more accurate solution of the inverse scattering problem near the end points. Improvements in accuracy due to the finite element solution are quantified using calculated attenuations from several bubble distributions of interest. [Work supported by ONT.]