Undersea Research Center

San Bartolomeo in Galdo, Italy

Undersea Research Center

San Bartolomeo in Galdo, Italy

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Vespe M.,Undersea Research Center | Greidanus H.,European Commission - Joint Research Center Ispra
IEEE Transactions on Geoscience and Remote Sensing | Year: 2012

Satellite-based synthetic aperture radar (SAR) is progressively becoming an operational asset for maritime monitoring applications. The services based on this technology rely on a level of image quality that, if not entirely fulfilled, may result in compromising the performance and accuracy of the intended application. Nonetheless, it is not always clear how to quantitatively measure the SAR image quality level from the delivered products. This paper discusses today's most relevant quality issues of satellite SAR images related to maritime applications. It introduces a set of quantitative measures that can be estimated from satellite images used in operational applications, not only to verify the conformity of the delivered image with respect to product specifications but also to assess how well the image can serve the application. To that end, the concept of application suitability is introduced, defined in relation to the specific application of interest. The focus is on oil spill detection and ship detection. © 1980-2012 IEEE.


Pastore T.,Undersea Research Center | Djapic V.,Undersea Research Center
Journal of Field Robotics | Year: 2010

Recent experimentation with autonomous surface vehicles (ASVs) has focused on the use of such platforms to perform tasks of classification or identification of objects first discovered by another sensor. The ASV generally carries small sensors capable of high-resolution imaging, but only at relatively short ranges. Reacquisition of a contact is inherent in the problem of classification and involves positioning of the surface vehicle with good precision such that the object of interest is in the field of view of the sensors aboard the ASV. This critical task of positioning the vehicle such that the classification sensors can be effectively brought to bear is the primary goal of our autonomy development. Experimental results from a variety of sensors are presented, but the most important in our present work has been a high-resolution multibeam imaging sonar operating at 450 kHz. This sensor has been successfully used to image divers and bottom objects, with telemetry data sent back to shore via wireless LAN. Although classification was done by a human operator ashore, the vehicle has the capability to keep an object in view of the sensor, representing an important operational advantage of the autonomy. Future work could expand the role of the unmanned platform to deployment of effectors-warning devices or entanglement devices in the case of harbor protection missions or neutralization devices in the case of countermine operations. © 2010 Wiley Periodicals, Inc.


Harrison C.H.,Undersea Research Center
Journal of the Acoustical Society of America | Year: 2011

The waveguide invariant, β, that manifests itself as interference fringes or striations in a plot of frequency vs source-receiver separation, is usually thought of as a modal phenomenon. This paper shows that striations can be explained simply through the variation of the eigenray arrival times with range, in short, the variation of the multipath impulse response. It is possible to calculate β for a number of sound speed profiles analytically and to find what β depends on, why it switches from one value to another, how it depends on source-receiver depth, how it depends on variable bathymetry, and how smooth the sound speed profile needs to be for clear fringes. The analytical findings are confirmed by calculating striation patterns numerically starting from eigenray travel times in various stratified environments. Most importantly the approach throws some light on what can be deduced from β alone and the likelihood and utility of striations in reverberation. © 2011 Acoustical Society of America.


Williams D.P.,Undersea Research Center
IEEE International Conference on Intelligent Robots and Systems | Year: 2011

A new algorithm for the detection of underwater objects in sonar imagery is proposed. One particularly novel component of the algorithm also detects the presence of, and estimates the orientation of, sand ripples. The overall algorithm is made extremely fast by employing a cascaded architecture and by exploiting integral-image representations. As a result, the method makes real-time detection of objects in streaming sonar data collected by an autonomous underwater vehicle (AUV) feasible. No training data is required because the proposed method is adaptively tailored to the environmental characteristics of the sensed data that is collected in situ. The flexible yet rigorous approach also addresses and overcomes five major limitations that plague the most popular detection algorithms that are in common use. Moreover, the proposed algorithm achieves superior performance across a variety of seabed types on a large, challenging data set of real sonar data collected at sea. Ways to exploit the findings and adapt AUV surveys for optimized detection performance are also suggested. © 2011 IEEE.


Williams D.P.,Undersea Research Center
Intelligent Service Robotics | Year: 2012

A new adaptive strategy for performing data collection with a sonar-equipped autonomous underwater vehicle (AUV) is proposed. The approach is general in the sense that it is applicable to a wide range of underwater tasks that rely on subsequent processing of side-looking sonar imagery. By intelligently allocating resources and immediately reacting to the data collected in-mission, the proposed approach simultaneously maximizes the information content in the data and decreases overall survey time. These improvements are achieved by adapting the AUV route to prevent portions of the mission area from being either characterized by poor image quality or obscured by shadows caused by sand ripples. The peak correlation of consecutive sonar returns is used as a measure for image quality. To detect the presence of and estimate the orientation of sand ripples, a new innovative algorithm is developed. The components of the overall data-driven path-planning algorithm are purposely constructed to permit fast real-time execution with only minimal AUV onboard processing capabilities. Experimental results based on real sonar data collected at sea are used to demonstrate the promise of the proposed approach. © 2011 The Author(s).


Alvarez A.,Undersea Research Center | Mourre B.,Undersea Research Center
Journal of Atmospheric and Oceanic Technology | Year: 2012

Ocean observing systems (OOSs) constituted by moorings and gliders are becoming relevant in oceanographic and climate studies. In these observing networks, the temporal variability is captured by mooring observations, while the spatial variability is obtained fromgliders sampling in the surrounding area. The advent of this observing capability brings the need to find optimal procedures to sample a given ocean region with a glider in the presence of a neighboringmooring, in order to maximize the information content of the data collected by this observing network. Different criteria (e.g., A, G, or E optimality) commonly used in the geosciences to obtain an optimumdesign lead to different sampling strategies. The question of which criterion performs better for optimal design in the marine environment remains open. This work investigates optimal procedures to sample a given ocean region with a glider in the presence of a mooring. Specifically, observing systems simulation experiments (OSSEs) are carried out in the Ligurian Sea (western Mediterranean) in August 2010 to study the different sampling strategies. Three criteria, which respectively aim at minimizing the trace (A optimal), maximum diagonal value (G optimal), and maximum eigenvalue of the error covariance matrix (E optimal), are considered. The resulting temperature field estimations are evaluated against a control field at 50-, 100-, and 150-m depth. The results indicate that the most appropriate strategy for environmental characterization using gliders employs the A optimal criterion, minimizing the mean uncertainty over the study area. © 2012 American Meteorological Society.


Williams D.P.,Undersea Research Center
Proceedings - IEEE International Conference on Robotics and Automation | Year: 2010

This work addresses the task of designing the optimal survey route that an autonomous underwater vehicle (AUV) should take in mine countermeasures (MCM) operations. It is assumed that the AUV is equipped with a side-looking sonar that is capable of generating high-resolution imagery of the underwater environment. The objective of the path-planning task is framed in terms of maximizing the success of detecting underwater mines in such imagery. Several commonly made - but inaccurate - assumptions about the problem are raised and refuted; it is demonstrated that mine detection performance depends on both range and seabed type. The issue of how to update detection probabilities when multiple views are obtained is also addressed. These various considerations are exploited in conjunction with synthetic aperture sonar (SAS) data to predict detection performance and efficiently design AUV routes that outperform standard ladder surveys. The proposed algorithm can be used to assess and quantify detection performance achieved in past, as well as future, missions. Because the entire route of the AUV can still be designed before deployment, no additional onboard processing or adaptive capabilities are required of the AUV. Therefore, the proposed approach can be immediately applied to systems conducting MCM operations at sea. The method is demonstrated on real SAS imagery collected by an AUV in the Baltic Sea. ©2010 IEEE.


Alvarez A.,Undersea Research Center | Mourre B.,Undersea Research Center
Journal of Atmospheric and Oceanic Technology | Year: 2012

This work investigates the merging of temperature observations from a glider fleet and remote sensing, based on a field experiment conducted in an extended coastal region offshore La Spezia, Italy, in August 2010. Functional optimal interpolation and spline formalisms are used to integrate temperature profiles from a fleet of three gliders with remotely sensed sea surface temperature into a volumetric thermal field estimate. Independent measurements from a towed ScanFish vehicle are used for validation. Results indicate that the optimal interpolation approach performs better than the spline model at and above the thermocline depth as long as anisotropic covariances computed from the remote sensing data are used. Below the thermocline, the two merging techniques give similar performance. © 2012 American Meteorological Society.


Williams D.P.,Undersea Research Center
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2010

This work exploits several machine-learning techniques to address the problem of image-quality prediction of synthetic aperture sonar (SAS) imagery. The objective is to predict the correlation of sonar ping-returns as a function of range from the sonar by using measurements of sonar-platform motion and estimates of environmental characteristics. The environmental characteristics are estimated by effectively performing unsupervised seabed segmentation, which entails extracting wavelet-based features, performing spectral clustering, and learning a variational Bayesian Gaussian mixture model. The motion measurements and environmental features are then used to learn a Gaussian process regression model so that ping correlations can be predicted. To handle issues related to the large size of the data set considered, sparse methods and an out-of-sample extension for spectral clustering are also exploited. The approach is demonstrated on an enormous data set of real SAS images collected in the Baltic Sea. ©2010 IEEE.


Harrison C.H.,Undersea Research Center
Journal of the Acoustical Society of America | Year: 2011

In active sonar the target echo level is often estimated with a propagation model that adds all multipath arrivals. If the (post-correlator) transmitted pulse is short compared to the multipath time spread then there is effectively an extra loss (which may be substantial) since only a few of the paths contribute to the target echo at any one instant. This well known time-smearing loss is treated in a self-consistent manner with previous calculations of reverberation [Harrison, J. Acoust. Soc. Am. 114, 2744-2756 (2003)] to estimate the target response and the signal-to-reverberation-ratio. Again isovelocity water, Lambert's law, and reflection loss proportional to angle are assumed. In this important short pulse regime the target response becomes independent of boundary reflection properties but proportional to transmitted pulse length. Thus the signal-to-reverberation-ratio becomes independent of pulse length. The effect on signal-to-ambient-noise is also investigated and the resulting formulas presented in a table. © 2011 Acoustical Society of America.

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