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Formal Reports

Report of results of completed projects or major milestones either in scientific terms or in terms acceptable to a wider audience. Note: Unless linked to the full text, reports are only available to NATO member nations from designated distribution centres. 

Documents

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Impact of seabed geoacoustic gradients and roughness on acoustic transmission into the sediment Impact of seabed geoacoustic gradients and roughness on acoustic transmission into the sediment

Date added: 11/06/2014
Date modified: 11/06/2014
Filesize: Unknown

Impact of seabed geoacoustic gradients and roughness on acoustic transmission into the sediment. Nielsen, Peter L. CMRE-FR-2014-018. October 2014.

Low-frequency (<50 kHz) sonars have advantages in detecting buried objects compared to high-frequency sonars (>100 kHz) because of lower attenuation of the acoustic field in the seabed. This allows the acoustic field to interact with a buried object, which upon reception may be used for detection and classification. The low attenuation is not the only environmental parameter that increases the probability of buried object detection. Acoustic propagation above the critical angle of the seabed naturally increases the penetration of the field into the seabed, but also seabed roughness, volume inhomogeneities, and excitation of particular waves have been proposed to enhance the penetration, even at propagation angles below the critical angle. One mechanism rarely considered to contribute to the acoustic penetration is the gradients of the geoacoustic properties. In this report the impact of these gradients on the acoustic penetration ratio is investigated by numerical modeling. The penetration ratio is here defined as the ratio of the acoustic pressure received one meter into the seabed and the incident pressure at the water-seabed interface. A model to predict the depth and frequency dependent geoacoustic properties is applied to generate inputs to a modified version of the full-field range-dependent propagation model RAM. The geoacoustic model has been validated against independent seabed models and data, and the acoustic model is well established in the underwater acoustics community, and is known to produce results at high fidelity level. The synthetic environment is intended to mimic an operational condition for the newly developed low-frequency mine hunting sonar at CMRE. Significant increase in penetration depth is observed when a geoacoustic profile is used compared to a seabed with the maximum constant properties of the profile. The impact of roughness on the penetration depth is also investigated by generating a rough water-seabed interface from a power law with parameters extracted from experimental data. Here the geoacoustic properties are assumed constant in depth. Minimum impact of the water seabed roughness on penetration ratio is observed in this case.

Sensor data management to achieve information superiority in maritime situational awareness Sensor data management to achieve information superiority in maritime situational awareness

Date added: 11/06/2014
Date modified: 11/06/2014
Filesize: Unknown

Sensor data management to achieve information superiority in maritime situational awareness. Cimino, Giampaolo; Arcieri, Gianfranco; Horn, Steven A.; Bryan, Karna. CMRE-FR-2014-017. October 2014.

This report describes the data handling process set up at the NATO Science & Technology Organization (STO) Centre for Maritime Research and Experimentation (CMRE) which includes sensor data acquisition, processing, storage and access in support of the Maritime Situational Awareness (MSA) project. The Database Management System (DBMS) and the way in which sensor data is acquired and loaded using a database access layer framework for client applications is described. The system has been designed and developed to cope with extremely large data volumes generated by sensors and it is the foundation for supporting the CMRE MSA Service Oriented Architecture and the Fusion on Demand concept. Many aspects of this system are then analyzed: data sensor parsing, real-time database loading, database structure, database data extraction (real-time and historical). This analysis is supported with performance figures for the use of the system with real data sets. This analysis demonstrates that the system is aneffective way to deliver relevant information to MSA decision makers. The whole system is currently deployed at CMRE.

A report on the proof-of-concept experiment (LLOMEx13) to use conventional 532nm LiDARs to measure vertical oceanographic properties A report on the proof-of-concept experiment (LLOMEx13) to use conventional 532nm LiDARs to measure vertical oceanographic properties

Date added: 10/30/2014
Date modified: 10/30/2014
Filesize: Unknown

A report on the proof-of-concept experiment (LLOMEx13) to use conventional 532nm LiDARs to measure vertical oceanographic properties. Trees, Charles. CMRE-FR-2014-016. October 2014.

During the Ligurian Sea LiDAR and Optical Measurement Experiment (LLOMEx'13) Sea Trial in March 2013, two conventional 532nm LiDAR systems were deployed making measurements of LiDAR waveforms concurrently with in situ profiling and towed platforms equipped with optical instrumentation. A significant portion of the LLOMEx'13 Sea Trial was devoted to a "Proof-of-Concept" for using LiDARs to vertical sample the water column for estimating oceanographic properties, specifically the Inherent Optical Properties (IOPs). The above-water LiDAR (MiniLiDAR) was a converted atmospheric LiDAR that was modified to withstand the maritime environmental conditions, as well as to operate close to the air-sea interface and still record the time gated returned laser signals. Because of weather conditions (rain, high seas and surface bulb formation), the MiniLiDAR had difficulty retrieving waveforms that were not contaminated by the surface interface or water drops that formed on both the laser and detector lens. The in situ profiling LiDAR system (Fine Structure Underwater Imaging LiDAR, FSUIL) performed superbly collecting vertical profiles of the LiDAR waveforms throughout most of the sea trial. During the FSUIL profiling, an IOP instrumented profiling platform (Multi-Angle SCattering Optical Tool, MASCOT) was simultaneously lower. The MASCOT measured spectral attenuation, absorption and scattering, thus providing the optical data necessary for the development of LiDAR algorithms to retrieve these properties from the reflected laser signals. A simplistic "single scattering" Radiative Transfer Equation (RTE) model was developed and tuned to the FSUIL data. The retrieved IOP data from the LiDAR waveform agreed well with that measured in situ by the MASCOT. Some fine tuning of the LiDAR RTE model is needed so that "multiple scattering" can be included in the solution. This inclusion should improve the accuracy of the optical retrievals as well as provide uncertainty budgets for these algorithms. A follow-on Sea Trial (LLOMEx) is proposed for late 2015 or early 2016 that would sample the Alboran Sea, which is a highly dynamical physical and optical region that also has persistent internal waves generated by the Straits of Gibraltar.

Real-time continuous active sonar processing Real-time continuous active sonar processing

Date added: 10/16/2014
Date modified: 10/16/2014
Filesize: Unknown

Real-time continuous active sonar processing. Canepa, Gaetano; Munafó, Andrea; Murphy, Stefan M. CMRE-FR-2014-015. September 2014.

This report describes the development of continuous active sonar (CAS) processing at CMRE. The software uses sub-band processing to achieve a faster update rate than is possible with pulsed active sonar (PAS). The software development was based on CMRE's PAS processing software, CAINPro, which has been thoroughly tested during previous sea trials and in post-processing data analysis. Computational efficiency was carefully considered and many optimizations were made so that the software can run in real-time using the constrained computing resources on board CMRE's Ocean Explorer autonomous underwater vehicles. The software was successfully tested during the REP14 Atlantic sea trial in July 2014, and was able to demonstrate real-time detection of an echo repeater on all nine sub-bands that were processed. The algorithm runs in real-time with a speed approximately six times faster than the original PAS software running equivalent processing.

Propagation and bistatic reverberation with convergence in a range-dependent environment: implementation in Artemis Propagation and bistatic reverberation with convergence in a range-dependent environment: implementation in Artemis

Date added: 09/11/2014
Date modified: 09/11/2014
Filesize: Unknown

Propagation and bistatic reverberation with convergence in a range-dependent environment: implementation in Artemis. Harrison, Chris H. CMRE-FR-2014-014. September 2014.

The flux formulation for propagation has already been modified to include ray convergence effects in a range-independent environment. This work is extended to include range-dependent propagation and bistatic reverberation suitable for direct insertion in the sonar performance model Artemis. The examples are run with a new implementation of Artemis that includes range-dependent convergence.

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