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Memorandum Reports

Report that covers interim results during the course of a project. Note: Unless linked to the full text, reports are only available to NATO member nations from designated distribution centres.

Documents

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Acoustic sensing of bottom properties using a VLA equipped underwater glider and naturally occurring ambient noise Acoustic sensing of bottom properties using a VLA equipped underwater glider and naturally occurring ambient noise

Date added: 06/22/2016
Date modified: 06/22/2016
Filesize: Unknown

Acoustic sensing of bottom properties using a VLA equipped underwater glider and naturally occurring ambient noise. Nielsen, Peter L. CMRE-MR-2016-005. June 2016.

Seabed properties are critical parameters for sonar performance predictions, and at the same time probably the most difficult information to acquire. Several techniques exist to establish localised geoacoustic properties by probes and advanced inversion schemes, but these methods are often inefficient, require surface vessels and significant human interaction, and are possibly computational intensive. Many of the techniques utilise active sound sources preventing anti-access/denied access operations and limitations in time duration and area coverage. The advancement in development of underwater glider technology combined with hydrophone arrays to measure naturally occurring ambient noise provides a very promising concept to conduct seabed property surveys efficiently. The glider operates almost without human interaction, and the hydrophone array acquires ambient noise to estimate seabed reflectivity and stratification. The ambient noise seabed characterisation has previously been demonstrated successfully using long moored and drifting hydrophone arrays, and the intention is to transition this approach to autonomous vehicles equipped with compact hydrophone arrays. As a part of the development process, CMRE conducted the GLIS-TEN?15 sea trial North of the Elba Island, Mediterranean Sea, where a section of the trial was dedicated to ambient noise measurements. A newly developed prototype survey system composed of a commercial SLOCUM glider equipped with a vertical hydrophone array was deployed to measure ambient noise, while the glider was hovering at depth as part of a series of dive sequences. This procedure samples the seabed properties spatially, and the derived seabed reflection properties and subbottom pro-filing are compared to estimates achieved from two moored reference hydrophone arrays. In general the glider based seabed reflection loss compares favourably to the results from the moored arrays although the loss is slightly lower for the glider data than the moored array data. Only the reflection off the bathymetry was observed from the glider data, while the moored arrays provide detailed seabed layering structure that matches almost perfectly to independent measurements. It is concluded that the glider array data are of poorer quality than the data acquired on the moored arrays, but this does not affect the generality of demonstrated concept.

Underwater acoustic source positioning using a small fleet of underwater gliders equipped with acoustic payload Underwater acoustic source positioning using a small fleet of underwater gliders equipped with acoustic payload

Date added: 06/16/2016
Date modified: 06/16/2016
Filesize: Unknown

Underwater acoustic source positioning using a small fleet of underwater gliders equipped with acoustic payload. Jiang, Yon-Ming, Garau Pujol, Bartolomé. CMRE-MR-2016-003. April 2016.

During the GLISTEN15 (Glider sensors and payloads for tactical characterization of the environment 2015) sea trial, which was conducted North of Elba Italy from 26 August to 09 September 2015, three omni-directional hydrophone-equipped gliders with reactive behaviour capability were deployed as a small glider network for testing its capabilities for maritime acoustic ISR. This report investigates the feasibility of using the fleet of three gliders to localize the signal of interest underwater by means of passive sensing. Two types of source localization algorithms, linearized and nonlinear, were developed and presented in this report. It is identified during the research that the linearized algorithm is suitable for being implemented in gliders for on board processing and for problems in a simple environment, and the nonlinear approach is capable of localizing the signal of interest in all environmental conditions but becomes more computationally demanding. Simulation and preliminary real data analysis showed that it is feasible to localize an acoustic source over 10 km away using a fleet of three gliders. Moreover, simulation results suggested that the algorithms required relative high precision of travel time measurements and also low inconsistency in the data acquisition systems between any two gliders. Hence it is concluded that better synchronization and consistency in data acquisition system of the glider fleet is crucial for applying the algorithms presented in this work to real world data. Further uncertainty analysis should be carried out to understand the quantified requirements, in travel time and glider positions, of the glider system.

Performance of CAS track optimization behavior from LCAS15 Performance of CAS track optimization behavior from LCAS15

Date added: 04/19/2016
Date modified: 04/19/2016
Filesize: Unknown

Performance of CAS track optimization behavior from LCAS15. Ferri, Gabriele. CMRE-MR-2016-004. April 2016.

In this report, a data-driven Mission Management Layer (MML) running on-board AUVs is described. MML manages all the phases of a littoral surveillance mission and exploits the characteristics of Continuous Active Sonar (CAS) signal pro-cessing. The MML selects for further investigation the tracks which are likely related to the presence of a target. In this case, the MML launches a receding horizon, non-myopic control algorithm which controls the AUV?s heading to improve the tracking performance to ease the target classification. The algorithm minimises the expected target position estimation error over a prediction time window by achieving a trade-off amongst different objectives: keeping the target at broadside, reducing the distance to the target, avoiding areas of high reverberation and searching for geometric configurations with low bistatic target localisation error. At-sea experiments performed during the LCAS15 sea trial are reported. They demonstrated, for the first time, that the proposed autonomy architecture can be executed together with real-time Continuous Active Sonar (CAS) processing on-board the AUVs. CAS has recently gained interest for littoral Anti-Submarine Warfare, as it offers the promise of multiple detections per waveform cycle. This can potentially improve the quality/length of tracks, thus increasing the adaptive behaviour?s performance, which, in turn, can increase the detection and tracking capabilities of the processing chain.

Multiple vessel routing in the GO-DSS: a flow network formulation Multiple vessel routing in the GO-DSS: a flow network formulation

Date added: 02/22/2016
Date modified: 02/22/2016
Filesize: Unknown

Multiple vessel routing in the GO-DSS: a flow network formulation. Bourque, François-Alex. CMRE-MR-2016-002. February 2016.

This contribution proposes to improve the Goal Oriented Decision Support System (GO-DSS) in light of previous results where a simpler vessel routing algorithm was shown to perform as well as the evolutionary algorithm implemented in the Optimal Asset Allocator (OAA) at a fraction of the computational cost. The prototyping builds on this work by implementing in the statistical analysis software R an alternative vessel routing algorithm using a minimum-cost flow network formulation of the problem. Planning is done at the tactical level, with a possible extension to operational planning via a rolling planning horizon left as a future contribution. As for the OAA, a set of time-ordered risk maps fusing various sources of information is the main input. Besides providing a net improvement in performance, the prototyped algorithm is also faster. Planning, however, is only possible for a fleet of homogeneous assets.

Experimental results on submarine detectability with continuous active sonar Experimental results on submarine detectability with continuous active sonar

Date added: 02/22/2016
Date modified: 02/22/2016
Filesize: Unknown

Experimental results on submarine detectability with continuous active sonar. Murphy, Stefan M. ; LePage, Kevin D. CMRE-MR-2015-004. April 2015.

Continuous active sonar (CAS) experimentation was conducted with an Italian diesel-electric submarine during the COLLAB-NGAS14 sea atrial. This report presents preliminary results and briefly describes the CAS-related components of the trial, including several issues encountered. A small subset of CAS data from one of CMRE’s AUVs was selected for full-band and sub-band processing. Analysis of this data subset resulted in a preliminary comparison of detection performance for various processing parameters. This report will be a useful guide for future analysis of CAS data collected during COLLAB-NGAS14.

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