313 research outputs found
Acoustic estimation of seafloor parameters: a Radial Basis Functions approach
A novel approach to the estimation of seafloor geoacoustic parameters from the measurement of the acoustic field in the water column is introduced. The approach is based on the idea of approximating
the inverse function that links the geoacoustic parameters with the measured field through a series
expansion of radial basis functions. In particular, Gaussian basis functions are used in order to
ensure continuity and smoothness of the approximated inverse. The main advantage of the proposed
approach relies on the fact that the series expansion can be computed off-line from simulated data
as soon as the experimental configuration is known. Data inversion can then be performed in true
real time as soon as the data are acquired. Simulation results are presented in order to show the
advantages and limitations of the method. Finally, some inversion results from horizontal towed
array data are reported, and are compared with independent estimates of geoacoustic bottom
properties
A task-priority based control approach to distributed data-driven ocean sampling
The paper illustrates the basic ideas and relevant algorithmic developments underlying the proposal for a task-priority based control approach to distributed data-driven ocean sampling applications. This approach is deemed allowing a better formalization of the overall motion problem of the involved team of agents; that apart the ultimate mission objective, also result characterized by other different control objectives directly related with both operability and safety aspects of the entire sampling system. Also, the proposed approach, other than leading to a unifying algorithmic structure, also seems allowing to foresee good possibilities for different types of downgrading toward efficient decentralized implementations
Geoacoustic seafloor exploration with a towed array in a shallow water area of the Strait of Sicily (2)
Acoustic propagation in shallow water is greatly
dependent on the geoacoustic properties of the seabottom. This
paper exploits this dependence for estimating geoacoustic sediment
properties from the bottom acoustic returns of known
signals received on a hydrophone line array. There are two major
issues in this approach: one is the feasibility of acoustic inversion
with a limited aperture line array, the other is related to the
knowledge of the geometry of the experimental configuration. To
test the feasibility of this approach, a 40-hydrophone4-m spaced
towed array together with a low-frequency acoustic source, was
operated at a shallow water site in the Strait of Sicily. In order to
estimate the array deformation in real time, it has been equipped
with a set of nonacoustic positioning sensors (compasses, tiltmeters,
pressure gauges). The acoustic data were inverted using
two complementary approaches: a genetic algorithm (GA) like
approach and a radial basis functions (RBF) inversion scheme.
More traditional methods, based on core sampling, seismic survey
and geophone data, together with Hamilton’s regression
curves, have also been employed on the same tracks, in order
to provide a ground truth reference environment. The results
of the experiment, can be summarized as follows: 1) the towed
array movement is not negligible for the application considered
and the use of positioning sensors are essential for a proper
acoustic inversion, 2) the inversion with GA and RBF are in
good qualitative agreement with the ground truth model, and 3)
the GA scheme tends to have better stability properties. On the
other hand, repeated inversion of successive field measurements
requires much less computational effort with RBF.The authors wish to acknowledge the master and crew of
the RN ALLIANCE and the SACLANT Centre Engineering
Department for their outstanding respective contributions in
the leadership, sea-going operation and equipment preparation
before and during the sea trial. The support of E. Dias
and E. Coelho from the Hydrographic Institute, Lisbon, on
the acquisition of the nonacoustic data and of P. Gershoft,
SACLANT Centre, on genetic algorithms setup, are also
appreciated. The authors wish also to express their appreciation
to the anonymous reviewers, whose comments have greatly
helped to reshape the second draft of this paper, and hopefully
to improve its readability
Mobile underwater sensor networks for protection and security: field experience at the UAN11 experiment
The EU-funded project UAN (Underwater Acoustic Network) was aimed at conceiving, developing, and testing at sea an innovative and operational concept for integrating underwater and above-water sensors in a unique communication system to protect offshore and coastline critical infrastructures. This work gives details on the underwater part of the project. It introduces a set of original security features and gives details on the integration of autonomous underwater vehicles (AUVs) as mobile nodes of the network and as surveillance assets, acoustically controlled by the command and control center to respond against intrusions. Field results are given of the final UAN project sea trial, UAN11, held in May 2011 in Norway. During the experimental activities, a UAN composed of four fixed nodes, two AUVs, and one mobile node mounted on the supporting research vessel was operated continuously and integrated into a global protection system. In this article, the communication performance of the network is reported in terms of round-trip time, packet loss, and average delivery ratio. The major results of the experiment can be thus summarized: the implemented network structure was successful in continuously operating over five days with nodes seamlessly entering and exiting the network; the performance of the network varied greatly with fluctuations in the acoustic channel; the addition of security features induced a minor degradation in network performance with respect to channel variation; the AUVs were successfully controlled from a remote station through acoustic signals routed by the network
Distributed Task-priority Based Control in Area Coverage & Adaptive Sampling
Abstract\u2014The paper presents the first simulative results and
algorithmic developments of the task-priority based control
applied to a distributed sampling network in an area coverage
or adaptive sampling mission scenario. The proposed approach
allowing the fulfilment of a chain of tasks with decreasing priority
each of which directly related to both operability and safety
aspects of the entire mission. The task-priority control is presented
both in the centralized and decentralized implementations
showing a comparison of performance. Finally simulations of
the area coverage mission scenario are provided showing the
effectiveness of the proposed approac
Attention Capture by Direct Gaze is Robust to Context and Task Demands
The final publication is available at Springer via https://dx.doi.org/10.1007/s10919-011-0128-z.Eye-tracking was used to investigate whether gaze direction would influence the visual scanning of faces, when presented in the context of a full character, in different social settings, and with different task demands. Participants viewed individual computer agents against either a blank background or a bar scene setting, during both a free-viewing task and an attractiveness rating task for each character. Faces with a direct gaze were viewed longer than faces with an averted gaze regardless of body context, social settings, and task demands. Additionally, participants evaluated characters with a direct gaze as more attractive than characters with an averted gaze. These results, obtained with pictures of computer agents rather than real people, suggest that direct gaze is a powerful attention grabbing stimulus that is robust to background context or task demands.103305-1/Canadian Institutes of Health Research89822-1/Canadian Institutes of Health Research103305-1/PHS HHS/United States89822-1/PHS HHS/United State
UAN: underwater acoustic network
Acoustic networks are for underwater what wifi is for terrestrial networks. The ocean is a nearly perfect media for acoustic waves in which regards long range propagation but poses a number of challenges in terms of available bandwidth, Doppler spread and channel fading. These limitations originate in the physical properties of the ocean, namely its anisotropy and boundary interaction which are particularly relevant in coastal waters where acoustic propagation becomes predominantly de- pendent on seafloor and sea surface properties. The acoustic communication channel is therefore multipath dominated and time and Doppler spread variable. The problem is aggravated when involving moving receivers as for instance when attempting to establish communication with or between moving autonomous underwater vehicles. The EU-funded project UAN - Underwater Acoustic Network aims at conceiving, developing and testing at sea an innovative and operational concept for integrating in a unique communication system submerged, surface and aerial sensors with the objective of protecting off-shore and coastline critical infrastructures. UAN went through various phases, including the development of hardware and software specific components, its testing independently and then in an integrated fashion, both in the lab and at sea. This paper reports on the project concept and vision as well as on the progress of its various development phases and the results obtained herein. At the time of writing, a final project sea trial is being planned and will take place two weeks before the conference so, although here we will concentrate on the progress obtained so far, the presentation at the conference may include additional results depending on the outcome of the sea trial
Body water distribution in severe obesity and its assessment from eight-polar bioelectrical impedance analysis
Objective: To measure body water distribution and to evaluate the accuracy of eight-polar bioelectrical impedance analysis (BIA) for the assessment of total body water (TBW) and extracellular water (ECW) in severe obesity. Design: Cross-sectional study. Setting: Obesity clinic. Subjects: In all, 75 women aged 18-66 y, 25 with body mass index (BMI) between 19.1 and 29.9 kg/m(2) (ie not obese), 25 with BMI between 30.0 and 39.9 kg/m(2) (ie class I and II obese), and 25 with BMI between 40.0 and 48.2 kg/m(2) (ie class III obese). Methods: TBW and ECW were measured by (H2O)-H-2 and Br dilution. Body resistance (R) was obtained by summing the resistances of arms, trunk and legs as measured by eight-polar BIA (InBody 3.0, Biospace, Seoul, Korea). The resistance index at a frequency of x kHz (RIx) was calculated as height 2/R-x. Results: ECW: TBW was similar in women with class III (46 +/- 3%, mean +/- s.d.) and class I-II obesity (45 +/- 3%) but higher than in nonobese women (39 +/- 3%, P < 0.05). In a random subsample of 37 subjects, RI500 explained 82% of TBW variance (P < 0.0001) and cross-validation of the obtained algorithm in the remaining 38 subjects gave a percent root mean square error (RMSE%) of 5% and a pure error (PE) of 2.1 l. In the same subjects, RI5 explained 87% of ECW variance (P < 0.0001) and cross-validation of the obtained algorithm gave a RMSE% of 8% and a PE of 1.4 l. The contribution of weight and BMI to the prediction of TBW and ECW was nil or negligible on practical grounds. Conclusions: ECW: TBW is similar in women with class I-II and class III obesity up to BMI values of 48.2 kg/m(2). Eight-polar BIA offers accurate estimates of TBW and ECW in women with a wide range of BMI (19.1-48.2 kg/m(2)) without the need of population-specific formulae
Localization of Autonomous Underwater Vehicles by Floating Acoustic Buoys: A Set-Membership Approach
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