Centre For Maritime Research And Experimentation Research Articles

The ONR three octave research array at Penn State

A new, large diameter towed research array has been built to support the experimental efforts of the Office of Naval Research (ONR) Ocean Acoustics Program. Array development was a collaborative effort between the Centre for Maritime Research and Experimentation (CMRE) in La Spezia, Italy, and the Penn State Applied Research Laboratory (PSU). PSU chose the array specifications based on discussions within the underwater acoustics community, prior measurement experience, cost efficiency, and flexibility in scientific measurements, while CMRE designed and assembled the array. The design includes three, forward-nested acoustic apertures cut for 1, 2, and 4 kHz, and hence, has been dubbed the Three Octave Research Array (THORA) in deference to its predecessor, the Five Octave Research Array (FORA). However, this system has a modular design to allow addition of acoustic apertures if scientific interest and sponsor support warrant. The array currently consists of a 50 m acoustic module and a 25 m vibration isolation module to help isolate the acoustic module from cable strum. This ship towed system has nearly 1 km of tow cable and a maximum measurement depth of 500 m. The array’s design, its use in the ONR NESMA23 Pilot experiment, and data quality will be discussed.

OCEANOGRAPHIC ENVIRONMENTAL ASSESSMENT USING UNDERWATER GLIDERS

REP(MUS) 21 is an annual exercise jointly organised by the Portuguese Navy, the University of Porto, NATO’s Centre for Maritime Research and Experimentation (CMRE) and the NATO Maritime Unmanned Systems Initiative. The exercise gives Allies and NATO partners a chance to field and evaluate new maritime technologies. A Rapid Environmental Assessment warfare group was formed using Maritime Unmanned Systems to perform an environmental assessment of this area, by collecting data from the upper ocean region (0- 200 m.), sea surface, littoral shallow waters, and river estuary. Underwater Gliders were used in the REPMUS21 exercise, brought by several partners, to conduct environmental observations from the underwater domain of the exercise’s Joint Operations Area (JOA). This paper focuses on the use of SeaExplorer underwater gliders to collect oceanographic data during the exercise, and the operational impact of using this knowledge to compile the Recognized Environmental Picture of the exercise area.

Use of towed array reverberation data for rapid environmental assessment

Towed array reverberation beam time series can provide information about the underwater acoustic environment by providing a snapshot of the scattering in both range and bearing. By mapping time into range and beam angle into azimuth, John Preston pioneered the use of polar plots to survey an area [Preston et al., J. Acoust. Soc. Am., 87,119–134 (1991)]. When the polar plot is superimposed on the bathymetry of an area, a scattering map can be made. High scattering is generally associated with bottom features. With additional analysis and modeling, bottom loss and scattering strengths can be obtained [Preston and Ellis, J. Marine Systems 78, S359–S371 (2009)]. This talk emphasizes results from the rapid environmental assessment (REA) Rapid Response exercises 1996–1998, a multi-nation collaboration organized by NATO MILOC (military oceanography). While transmission loss experiments along a single radial could take hours, a single charge dropped near the towed array gave information on all radials in just minutes. Anomalies could be immediately identified, for investigation by more precise techniques. The REA exercises attracted interest and led to the Boundary Characterization and Clutter Joint Research Projects between CMRE (the NATO Centre for Maritime Research and Experimentation), Canada, and US. [Work supported by ONR.]

Cooperative Localization and Multitarget Tracking in Agent Networks with the Sum-Product Algorithm

This paper addresses the problem of multitarget tracking using a network of sensing agents with unknown positions. Agents have to both localize themselves in the sensor network and, at the same time, perform multitarget tracking in the presence of clutter and miss detection. These two problems are jointly resolved using a holistic and centralized approach where graph theory is used to describe the statistical relationships among agent states, target states, and observations. A scalable message passing scheme, based on the sum-product algorithm, enables to efficiently approximate the marginal posterior distributions of both agent and target states. The proposed method is general enough to accommodate a full multistatic network configuration, with multiple transmitters and receivers. Numerical simulations show superior performance of the proposed joint approach with respect to the case in which cooperative self-localization and multitarget tracking are performed separately, as the former manages to extract valuable information from targets. Lastly, data acquired in 2018 by the NATO Science and Technology Organization (STO) Centre for Maritime Research and Experimentation (CMRE) through a network of autonomous underwater vehicles demonstrates the effectiveness of the approach in a practical application.

DIVE: A distributed ID assignment and topology discovery protocol for underwater acoustic networks

This paper presents the DIVE protocol, which is designed to self assign unique node IDs in an underwater acoustic network. DIVE, which stands for Distributed Id assignment and topology discoVEry, is fully distributed and does not assume any prior knowledge of the network. One of the objectives of the DIVE protocol is the assignment of short IDs to the node, thus reducing the number of bits required to encode this information. Link quality information is explored to increase the robustness of the protocol against message losses. While discovering the network and assigning short node IDs, control data is shared to collect additional information about the network nodes, such as the type (static or mobile) and the number of hops to reach them. This information then can be used to support network operations. The protocol performance has been evaluated via simulations and during two at-sea campaigns: the 2016 Recognized Environmental Picture exercise (REP16), conducted in the Atlantic Ocean, and the 2017 Communications Network trial (CommsNet17), conducted by the NATO Science and Technology Organization Centre for Maritime Research and Experimentation (CMRE) in the Gulf of La Spezia, Italy. A variety of networking scenarios have been explored to validate the proposed solution, including node mobility as well as node addition and removal. The results show that DIVE is an efficient and reliable solution for node ID assignment and network discovery that scales with the network size in the presence of an unreliable communication channel. Additionally, when compared to a state-of-the-art solution, the usage of short IDs can significantly reduce the energy consumption and prolong the network lifetime.

The 2019 JANUS Interoperability Fest: A Field Report

Abstract Underwater acoustic communications are currently implemented through a variety of vendor-specific protocols. The lack of interoperability between these protocols has prompted the North Atlantic Treaty Organization (NATO) Science and Technology Organization (STO) Centre for Maritime Research and Experimentation (CMRE) to lead a collaborative effort toward the establishment of a standard for digital underwater acoustic communications. The JANUS standard was promulgated as a NATO standard, Standardization Agreement (STANAG) 4748, in March 2017 and has since been used by a growing number of vendors.To promote interoperability and engagement with industry, CMRE began organizing the JANUS Interoperability Fest. The goal of this event was to collectively exercise JANUS implementations from companies and to clear up any possible misunderstandings with the technical specification. The first edition of the JANUS Fest took place in 2018. This article describes the planned and performed tests as well as the primary outcomes of the second JANUS Fest, which was organized in 2019. The success of this event is demonstrated by the results and the positive feedback from participants and observers.

Interoperability Among Unmanned Maritime Vehicles: Review and First In-field Experimentation.

Complex maritime missions, both above and below the surface, have traditionally been carried out by manned surface ships and submarines equipped with advanced sensor systems. Unmanned Maritime Vehicles (UMVs) are increasingly demonstrating their potential for improving existing naval capabilities due to their rapid deployability, easy scalability, and high reconfigurability, offering a reduction in both operational time and cost. In addition, they mitigate the risk to personnel by leaving the man far-from-the-risk but in-the-loop of decision making. In the long-term, a clear interoperability framework between unmanned systems, human operators, and legacy platforms will be crucial for effective joint operations planning and execution. However, the present multi-vendor multi-protocol solutions in multi-domain UMVs activities are hard to interoperate without common mission control interfaces and communication protocol schemes. Furthermore, the underwater domain presents significant challenges that cannot be satisfied with the solutions developed for terrestrial networks. In this paper, the interoperability topic is discussed blending a review of the technological growth from 2000 onwards with recent authors' in-field experience; finally, important research directions for the future are given. Within the broad framework of interoperability in general, the paper focuses on the aspect of interoperability among UMVs not neglecting the role of the human operator in the loop. The picture emerging from the review demonstrates that interoperability is currently receiving a high level of attention with a great and diverse deal of effort. Besides, the manuscript describes the experience from a sea trial exercise, where interoperability has been demonstrated by integrating heterogeneous autonomous UMVs into the NATO Centre for Maritime Research and Experimentation (CMRE) network, using different robotic middlewares and acoustic modem technologies to implement a multistatic active sonar system. A perspective for the interoperability in marine robotics missions emerges in the paper, through a discussion of current capabilities, in-field experience and future advanced technologies unique to UMVs. Nonetheless, their application spread is slowed down by the lack of human confidence. In fact, an interoperable system-of-systems of autonomous UMVs will require operators involved only at a supervisory level. As trust develops, endorsed by stable and mature interoperability, human monitoring will be diminished to exploit the tremendous potential of fully autonomous UMVs.

2D Forward Looking SONAR in Underwater Navigation Aiding: an AUKF-based strategy for AUVs

This paper proposes an underwater navigation system where linear speed estimations, obtained with a 2D Forward-Looking SONAR (FLS), are integrated within a navigation filter and this solution is shown to work satisfyingly in the absence of Doppler Velocity Log (DVL) readings. Both to provide a better description of the system, which is a dynamic entity in a dynamic environment and to characterize FLS measurements, an Adaptive Unscented Kalman Filter (AUKF)-based estimator is here proposed. The solution has been tested and validated offline making use of navigation data obtained during sea trials performed in July 2018 with FeelHippo AUV at the basin of the NATO Science and Technology Organization Centre for Maritime Research and Experimentation (CMRE), La Spezia (Italy).

Continuous Active Sonars for Littoral Undersea Surveillance

Recent advances in transducer and computing technology have pushed the concept of continuous active sonar (CAS) or high duty cycle sonar as an area of interest for application to antisubmarine warfare. Unlike conventional pulsed active sonars, CAS processing aims at detecting echoes while transmitting with a nearly 100% duty cycle. This paper describes the signal processing chain developed at the Centre for Maritime Research and Experimentation (CMRE), La Spezia, Italy, for real-time CAS processing within an autonomous networked multistatic sonar system. The algorithm uses subband processing, which can potentially provide a higher target update rate than the traditional pulsed active sonar, while maintaining the same search radius. The higher rate of contact information can improve target tracking performance. Performance results are given from the COLLAB-NGAS14 sea trial where the CAS processor was deployed on two autonomous underwater vehicles (AUVs) acting as receivers of the CMRE experimental multistatic demonstrator. Results show the feasibility of the CAS concept in littoral scenarios, using AUVs as real-time receivers.

Underwater sensing and surveying with autonomous vehicles

The increasing capabilities of autonomous underwater vehicles is leading to a variety of new possibilities for underwater sensing and surveying. Portland State University and the Centre for Maritime Research and Experimentation (CMRE) have been working for several years on developing capabilities for underwater sensing with autonomous vehicles- mainly gliders or hybrid glider/powered vehicles. These vehicles have long deployment durations (weeks to months) but move relatively slowly. Two applications have been the focus of the work, seabed characterization and marine mammal population density estimation. For seabed sensing, the ambient noise field (e.g., breaking wave sounds) is being used as the sound source but one of the challenges for this method has been the limitations on the size of the hydrophone receiver array that can be deployed from the vehicle. For the marine mammal population density studies a glider has been customized with two hydrophones on the wings and various species are localized in bearing using time difference of arrival methods. Previous density estimation methods used a single, fixed hydrophone. In this presentation, experiments, challenges, and results will be described from several studies using autonomous vehicles for seabed characterization and marine mammal population density estimation.

Sediment characterization from normal incidence bottom loss at the GLISTEN sea test

The GLider Sensors and payloads for Tactical characterization of the ENvironment (GLISTEN) sea test was conducted off the west coast of Italy in August of 2015. Led by the Centre for Maritime Research and Experimentation (CMRE), the effort included seven other international organizations including the Applied Research Laboratories from The University of Texas at Austin (ARL:UT). The mission of the sea test was to improve and understand long-range acoustic methods of environmental characterization in shallow waters. As part of the test, a team from ARL:UT deployed a remotely operated vehicle (ROV) which collected normal incidence bottom loss data from 6 to 20 kHz along with video and laser line profiling data. These data were taken along the propagation paths of the CMRE low-frequency transmission loss experiment. In this presentation, results will be shown from the bottom loss measurements for a variety of sediments that included both layering and entrained gas pockets. The acoustic data will be compared ...

Mission Planning and Decision Support for Underwater Glider Networks: A Sampling on-Demand Approach.

This paper describes an optimal sampling approach to support glider fleet operators and marine scientists during the complex task of planning the missions of fleets of underwater gliders. Optimal sampling, which has gained considerable attention in the last decade, consists in planning the paths of gliders to minimize a specific criterion pertinent to the phenomenon under investigation. Different criteria (e.g., A, G, or E optimality), used in geosciences to obtain an optimum design, lead to different sampling strategies. In particular, the A criterion produces paths for the gliders that minimize the overall level of uncertainty over the area of interest. However, there are commonly operative situations in which the marine scientists may prefer not to minimize the overall uncertainty of a certain area, but instead they may be interested in achieving an acceptable uncertainty sufficient for the scientific or operational needs of the mission. We propose and discuss here an approach named sampling on-demand that explicitly addresses this need. In our approach the user provides an objective map, setting both the amount and the geographic distribution of the uncertainty to be achieved after assimilating the information gathered by the fleet. A novel optimality criterion, called , is proposed and the resulting minimization problem is solved by using a Simulated Annealing based optimizer that takes into account the constraints imposed by the glider navigation features, the desired geometry of the paths and the problems of reachability caused by ocean currents. This planning strategy has been implemented in a Matlab toolbox called SoDDS (Sampling on-Demand and Decision Support). The tool is able to automatically download the ocean fields data from MyOcean repository and also provides graphical user interfaces to ease the input process of mission parameters and targets. The results obtained by running SoDDS on three different scenarios are provided and show that SoDDS, which is currently used at NATO STO Centre for Maritime Research and Experimentation (CMRE), can represent a step forward towards a systematic mission planning of glider fleets, dramatically reducing the efforts of glider operators.

Typhoon at CommsNet13: Experimental experience on AUV navigation and localization

This paper presents two acoustic-based techniques for Autonomous Underwater Vehicle (AUV) navigation within an underwater network of fixed sensors. The proposed algorithms exploit the positioning measurements provided by an Ultra-Short Base Line (USBL) transducer on-board the vehicle to aid the navigation task. In the considered framework the acoustic measurements are embedded in the communication network scheme, causing time-varying delays in ranging with the fixed nodes. The results presented are obtained with post-processing elaborations of the raw experimental data collected during the CommsNet13 campaign, organized and scientifically led by the NATO Science and Technology Organization Centre for Maritime Research and Experimentation (CMRE). The experiment involved several research institutions and included among its objectives the evaluation of on-board acoustic USBL systems for navigation and localization of AUVs. The ISME groups of the Universities of Florence and Pisa jointly participated to the experiment with one Typhoon class vehicle. This is a 300 m depth rated AUV with acoustic communication capabilities originally developed by the two groups for archaeological search in the framework of the THESAURUS project. The CommsNet13 Typhoon, equipped with an acoustic modem/USBL head, navigated within the fixed nodes acoustic network deployed by CMRE. This allows the comparison between inertial navigation, acoustic self-localization and ground truth represented by GPS signals (when the vehicle was at the surface).

The SUNSET framework for simulation, emulation and at-sea testing of underwater wireless sensor networks

The Sapienza University Networking framework for underwater Simulation Emulation and real-life Testing (SUNSET) is a toolkit for the implementation and testing of protocols for underwater sensor networks. SUNSET enables a radical new way of performing experimental research on underwater communications. It allows protocol designers and implementors to easily realize their solutions and to evaluate their performance through simulation, in-lab emulation and trials at sea in a direct and transparent way, and independently of specific underwater hardware platforms. SUNSET provides a complete toolchain of pre-deployment and deployment time tools able to identify risks, malfunctioning and under-performing solutions before incurring the expense of going to sea. Novel underwater systems can therefore be rapidly and easily investigated. Heterogeneous underwater communication technologies from different vendors can be used, allowing the evaluation of the impact of different combinations of hardware and software on the overall system performance. Using SUNSET, underwater devices can be reconfigured and controlled remotely in real time, using acoustic links. This allows the performance investigation of underwater systems under different settings and configurations and significantly reduces the cost and complexity of at-sea trials. This paper describes the architectural concept of SUNSET and presents some exemplary results of its use in the field. The SUNSET framework has been extensively validated during more than fifteen at-sea experimental campaigns in the past four years. Several of these have been conducted jointly with the NATO STO Centre for Maritime Research and Experimentation (CMRE) under a collaboration between the University of Rome and CMRE.

Synthetic aperture sonar imaging of breaking internal wave structures

In October 2012, the Centre for Maritime Research and Experimentation (CMRE) conducted the ARISE’12 trials from the NATO research vessel Alliance, off of Elba island, Italy. During this trial, data were collected by the Norwegian Research Defence Establishment (FFI) using a HUGIN AUV with interferometric synthetic aperture sonar (SAS). Large visible structures in the SAS images and in the SAS bathymetries were caused by features in the water column, called boluses, which formed after breaking internal wave events. Variation in backscattered intensity from the seabed was caused by focusing of sound by the bolus and errors in bathymetry by the changes in phase as the acoustic energy moved through the lower sound speed bolus. A ray model and a 3D parabolic equation (PE) model were used to simulate the effects of the bolus on the acoustic field incident on the bottom and results compared favorably with SAS data. Models for the change in bolus size and speed as it propagated upslope also gave reasonable comparison to estimates obtained from SAS intensity images. [The work performed by APL was supported by the US Office of Naval Research.]

Impact of Time-Varying Underwater Acoustic Channels on the Performance of Routing Protocols

The recent development of underwater acoustic modems has enabled multihop networking capabilities that can be used in important military and civilian applications. For this reason, routing protocols for underwater acoustic networks (UANs) have recently been proposed and evaluated. However, the interactions between channel dynamics and networking performance are not well understood. In this paper, we investigate and quantify the effect of the time-varying (TV) link quality on routing protocols in static UANs. In order to do so, we simulate the considered routing protocols in several network scenarios, obtained by changing the network density, the number of packet retransmissions, the packet length, the modulation type, and the power level with both TV and time-invariant (TI) channel conditions. Results confirm that, when evaluating the performance of routing protocols, it is important to understand the TV behavior of the channel quality over intervals of time sufficiently long to accommodate multihop communications. Finally, we also present experimental results, confirming the outcome of the simulations. The experiments have been conducted in collaboration with the NATO Centre for Maritime Research and Experimentation (CMRE) during the CommsNet12 sea trial.