Browse Publications
2011 Reports
Note: Unless linked to the full text, reports are only available to NATO member nations from designated distribution centres.
A matlab package for mission generation of a fleet of gliders. Version 1.0. Alvarez, A.; Martinez, M. NURC-SP-2011-003. November 2011
The advent of new ocean observing technologies creates new scientific demands. Integrating oceanographic information and harmonizing different observational capabilities are among them. The latter concerns allocating and complementing observational resources to maximize the information content of the oceanographic data collected by a network of different oceanographic platforms. Compatibility between the observing capabilities of the different nodes must be found designing optimum sampling strategies to allow an accurate representation of oceanographic process. These sampling strategies could adapt to the evolution of the environment, considering possible motion limitations of part of the platforms in the network. This report describes a software developed to increase the optimality of sampling missions of a network of underwater gliders that may differ in control and motion capabilities. The procedure employs a statistical model of the spatial variability in the area of interest, extracted from a numerical model. The statistical model is then employed to compute sampling designs minimizing the spatial average variance of the estimated field with respect to the sampled locations. Simulated Annealing is employed as the minimization procedure to find the optimal trajectories of the autonomous platforms. The resulting optimum sampling design incorporates existing operational constraints and platform limitations.
Report on the ACommsNet10 cruise. Potter, J.; Berni, A.; Alves, J.; Merani, D.; Zappa, G. NURC-FR-2011-007. October 2011.
The ACommsNet10 experiment consisted of several connected experimental modules, including the testing of several Media Access Control (MAC) protocols under different application conditions, the testing of a Delay and Disruption Tolerant (DTN) networking implementation and of a new low-overhead routing protocol and implementation developed at NURC. The NURC Modem-ona-Rope (MoaR) was used, consisting of three tripods with modems, connected via fibre-optic cable and power lines to shore at the Parco Nazionale Arcipelago di Toscana island of Pianosa. The CRV Leonardo was used to conduct bathymetric surveys, to install and recover the MoaR and to provide a mobile communications node via her moon pool. Other mobile nodes included Rigid Hull Inflatable Boats (RHIBs) with modems controlled by University of Porto-provided 'MANTA' systems (controlled via a Freewave link to shore) and eFolagas with micro-modems on board. A gateway buoy with a WHOI micro modem was also deployed for the majority of the experiment, until a failed antenna put it out of action. The performance trade-offs between CSMA, T-LOHI and DACAP MAC protocols were explored, supporting the general conclusions obtained from simulation. CSMA works well for low traffic and asymmetric links. DACAP maintains better performance for high offered loads, but has a high overhead and is badly affected by asymmetric links. Using acknowledgements rarely improves performance and can be disastrous if a link is strongly asymmetrical. The DTN implementation worked well, with some initial modifications to the reference implementation designed and implemented during the trial creating up to 100% improvements in efficiency in the underwater network. The low-overhead routing protocol also worked well and work is now focusing on optimising the various metrics used for weighting decisions and in integrating the routing with other protocols, such as MAC and DTN.
A Fast Detection Algorithm for Autonomous Mine Countermeasures. Williams, D.P.; Groen, J.; Fox, W.L.J. NURC-FR-2011-006. October 2011.
A new algorithm for the detection of underwater mines 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 mines in streaming sonar data collected by an autonomous underwater vehicle (AUV) feasible. No training data are required because the proposed method is adaptively tailored to the environmental characteristics of the sensed data that are collected in situ. The flexible yet rigorous approach also addresses and overcomes four 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.
Supervised Track Classification in Support of AUV Decision Making. Sildam, J.; Ehlers F. NURC-FR-2011-008. October 2011
In the context of off-board multi-static experiments for antisubmarine warfare, autonomous underwater vehicles (AUVs) will have to be programmed to detect and track targets in real time. The state of the art is to form tracks by associating detections from consecutive pings, whereby normally the association is made using kinematic features. If, however, the clutter or false alarm density is too high for the sensor resolution given by the system design, false track associations are likely, which cannot be resolved during post-processing or by the multi-static set-up. That is the scenario when classification of all detections associated by a tracker is necessary. To perform such a classification, snippets of time series associated with respective detections are required. In this work we propose a heuristic feature construction approach that can be used for track classification at computational cost suitable on board of AUV. We construct the proposed discrete feature in two steps. In the first step, to avoid making any explicit assumptions about probability function underlying the noise- or signal generating process, we conduct the Maximum Mean Discrepancy (MMD) test, which instead of testing two hypothesis on a single time-snippet, applies the MMD test on a couple of sets of normalized data snippets around real-time generated contact data. For each ping, by applying the MMD test on detections on a fine bearing range grid, we obtain the distribution of a distance measure d that quantifies the degree of dissimilarity between sets of normalized data snippets around real-time generated contact data. In a second step, we estimate the difference of entropies of the d-distribution in bearing and range directions respectively over the sequence of contacts forming the tracks, and use this entropy difference as a robust statistical feature. By carefully analysing data from NURC’s bi-static and multi-static sonar field experiments GLINT09 and GLINT10, we construct tracks associated with contacts of echoes (a) from bottom structures, and (b) Generated Signals from Echo-Repeater or direct blast. We investigate the feasibility of the proposed feature construction approach in a framework of supervised classification approaches using generative (Hidden Markov Model, Naive Bayes), and discriminative (Conditional Random Field) models. This work will be extended to the unsupervised learning, and the results of this extended work will be applied to GLINT11 data.
Adiabatic Reverberation and Target Echo Mode Incoherent Sum "ARTEMIS". Harrison, C. NURC-FR-2011-009. November 2011
ARTEMIS is a very fast sonar performance model including target echo strength and reverberation for bistatic arrangement in an arbitrary range dependent environment with arbitrary sound speed variation. Outputs are three dimensional, and they can be presented in map form as target echo, reverberation or signal-to reverberation- ratio. This capability is rare amongst the many other existing reverberation models. It is based on the adiabatic approximation, and gets its speed by performing an incoherent mode sum over a continuum of WKB modes and interpolating from wavenumber to mode number. Three variants exist: one assumes a single target position (with corresponding reverberation) as is required by MSTPA; two others assume many hypothetical target positions to form a map of target echo and reverberation. In the latter two, acoustic WKB calculations are first done on a coarse rectangular grid, and these are spatially interpolated along radials from the source and receiver. Finally results are interpolated to a fine rectangular grid. The distinction between the last two variants is the order in which spatial and wavenumber interpolation are carried out. All these approaches evolved from the analytical solutions for isovelocity but with variable bathymetry.
Development of a real-time multistatic ASW simulation facility at the NATO Undersea Research Centre. Strode, C.; Oddone, M.; Leonard, M. NURC-FR-2011-005. August 2011
The following report details the integration of the Multistatic Tactical Planning Aid (MSTPA) with the OpenSea augmented reality facility at NURC. In such a configuration the position of Anti Submarine Warfare (ASW) assets are sent to MSTPA which returns realistic contacts, tracks, and classifications to a simulated tactical display. This allows for the creation of a real time multistatic simulation capability in which operators may drive surface platforms, helicopters, and submarines through a realistic acoustic environment in order to develop multistatic ASW tactics.
Algorithmic analysis of the NURC SAS processing chain. Schmaljohann, H.; Groen, J. NURC-MR-2011-003. August 2011
In this document the main parts of the SAS processing program based on the MATLAB code at NURC are displayed in a flow chart, and the different processing steps are summarized. The text should provide some help for those who want to work with the NURC SAS processing chain. Be aware that the less relevant details (i.e., those which are only included for a faster processing) are not listed in this text.
The Multistatic Tactical Planning Aid (MSTPA) - User Guide. Strode, C.; Oddone, M. NURC-SP-2011-002. August 2011
This overview is designed to introduce the user to the major functionality of the Multistatic Tactical Planning Aid in order to facilitate its use within both the scienti c and operational maritime communities. The guide begins with installation instructions followed by a description of the major components of the input le format. This includes the environmental and propagation model details together with sensor and platform motion components. Example output le format is then described together with Matlab code to facilitate more detailed plotting and analysis functionality. The optimisation mode of the tool is introduced and described by means of simple example scenarios. Finally, the batch processing mode is described such that the core acoustic and contact generation modules may be used to generate results while suppressing any graphical output. This may be used to incorporate MSTPA into existing simulation frameworks.
ITMINEX 2011 - Percentage Clearance Trials Analysis. Strode, C. NURC-FR-2011-004. July 2011
During exercise ITALIAN MINEX 2011 2 minehunters conducted percentage clearance trials in the La Spezia harbour area. NURC was involved in the planning and subsequent analysis of these trials. On this occasion the MINEX was conducted in conjunction with the NURC ARISE11 experiment. This allowed for the completion of a detailed synthetic aperture sonar (SAS)survey of the PC trial area by the MUSCLE AUV. This report presents the results of the analysis for distribution to the commanding officers of the participating units.
Waterside Security 2010 (WSS2010) Conference: Post Conference Report. Kessel, R.; Zakharia, M. NURC-MR-2011-002. February 2011
The 2nd International Conference on Waterside Security was hosted by NURC, Carrara, Italy, 3-5 November 2010. This report provides summary statistics of the conference, a summary of the workshops, remarks form the WSS2010 Chairman (Ronald Kessel), and acknowledges key contributors.
Performance metrics for next-generation underwater surveillance networks. Casari, P.; Berni, A.; Merani, D.; Zorzi, M. NURC-FR-2011-002. June 2011
This report presents performance metrics (e.g., survivability, probability of message delivery, etc.) that are relevant for the definition and simulation of operational conditions and C2 processes in underwater networks, and for the extension of current, well established, tactical decision aids to include awareness of this new network-enabled problem space. An overview of the metrics used for the characterization of performance in wireless networks is provided, dividing the metrics according to the network layer they are applicable to, and giving indications on cross-relationships and on the assessment of protocol performance by observing their general behavior. A theoretical case study is presented, where these concepts are applied to the comparison of four protocols for underwater networking. The interplay between the metrics and the specific scenarios and applications they relate is highlighted, observing the possibility of defining more specific and useful metrics through a more detailed description of the application that has to be served. In the conclusions we observe that application performance is the ultimate benchmark for understanding whether the supporting configuration and setup of networks and protocols is adequate to meet the operational requirement, stressing that a tradeoff can usually be found between the application-specific quality requirements and the load the network can actually support.
Underwater Sensor Networks: requirements for Cooperative ASW, functional components, network modelling approaches. Berni, A.; Merani, D.; Casari, P.; Zorzi, M. NURC-FR-2011-003. June 2011
In this report we present an initial overview or requirements, functional components and modelling approaches towards a Cooperative ASW (CASW) network architecture. We start introducing capabilities and requirements of the different system components (fixed nodes for local passive detection, mobile nodes for flexible target characterization and tracking, gateways to command and control networks) following a system-of-systems approach, to address the different subsystems from a functional perspective. We then present a taxonomy of communications requirements for CASW, putting it in context with current communications capabilities and constraints. In the following overview of underwater networking, we will discuss the reasons behind the inefficiency of the Internet Protocol in the underwater environment, proposing the use of Delay/Disruption Tolerant Networking (DTN) as a way to address specific challenges, delivering added-value features that are relevant to maritime networking. In the final section, we will introduce the use of the MIRACLE extensions to the ns2 network simulator, to provide a modelling capability for underwater networking and a useful tool for system performance studies and mission planning. Although this report covers underwater networking from the perspective of the CASW application, the methodology followed and the abstractions that derive from it may be applied to a broader scope of applications. Future work will focus on the identification of performance metrics relevant to the application being considered, and on the actual engineering developments required to enable at-sea experimentation of the proposed concepts.
NURC SWATH-USV Concept design and hydrodynamic optimization of an innovative SWAT-Hull form by CFD methods. Brizzolara, S.; Curtin, T.; Bovio, M.; Vernengo, G. NURC-SP-2011-001. June 2011.
The report presents the main characteristics and functions of an innovative platform which has been conceived and designed to extend the operational capabilities of current Unmanned Surface Vehicles (USV) in terms of platform stability in waves and of powering requirement at relatively high speed. The main idea which governs the project is the realization of a small autonomous surface unit (6m in overall wetted length) capable of undertaking several tasks in the marine environment even in moderate rough sea conditions. The designed vessel has mainly the ability to locate, recover and launch other members of the autonomous fleet (like AUVs or other underwater devices) and at the same time could carry out a surveillance service of the surrounding areas. To manage with these tasks the vehicle is build to provide a fairly good autonomy which is needed to face with intermediate range missions (100 nautical miles). The choice of a SWATH, Small Waterplane Area Twin Hull form has been motivated by its excellent properties of seakeeping quality, which is combined with a non conventional low resistance underwater hull shape which is able to reduce to a minimum the resistance of the vessel especially at higher speeds. The excellent seakeeping performance are due to the small area of the waterline figure which determine a low reactivity to wave’s exciting forces and moments. The result is a incomparably stable platform when compared to equivalent conventional monohull or catamaran platform solutions. Moreover, the innovative geometry of the immersed part of the hull lowers the advance resistance thanks to a positive interference effect between the generated wave trains. To obtain the most efficient profile of the underwater bodies a systematic optimization with an automatic procedure have been arranged for the purpose. This is based on a parametric definition of the geometry, a CFD solver and a differential evolution global minimization algorithm. Many experimental data have been verified to test the ability of the software to predict resistance. Simulations have been made both in the air and in the water to compare software’s result with original one and to verify its goodness. As expected all the CFD computations have demonstrated the well superior efficiency of the developed unconventional SWATH technology with respect to current alternatives of hull typologies. The report, after presenting the main characteristics of the vessel and its hydrodynamic properties, describes more in details the concept design following the usual items of the design spiral used by naval architects. So hull form design, hydrostatic properties, main structural layout and dimensioning, weight estimation, intact stability, powering requirement and propulsion layout, auxiliary systems, i.e. active stabilization systems and AUV launching and recovering systems, in our case.
The relation between the waveguide invariant, multipath impulse response, and ray cycles. Harrison, C. NURC-FR-2011-001. February 2011.
The waveguide invariant, beta, 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 report 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 beta for a number of sound speed profiles analytically and to see what beta 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 beta alone and the likelihood and utility of striations in reverberation.
Spectrofluorometric and HPLC Chlorophyll-a measurement comparison. Ampolo Rella, M. NURC-MR-2011-001. January 2011
To address uncertainties inherent in fluorescence in vitro analysis and the measurement of chlorophyll a, this study was conducted to develop a set of crossreferenced samples analyzed using both spectrofluorometry and high performance liquid chromatography (HPLC). A linear regression was developed between the two methodologies, and coefficients are now being applied to spectrofluorometric measurements to improve chlorophyll a data results at the NATO Undersea Research Centre (NURC) Oceanographic Branch Laboratory.