Sunday, December 17, 2017
      CMRE Facebook page  CMRE LinkedIn page  CMRE PAO Youtube page
   
Text Size
CMRE banner

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

Order by : Name | Date | Hits [ Descendent ]

Multipath pulse shapes with refraction Multipath pulse shapes with refraction

Date added: 04/01/2006
Date modified: 06/22/2012
Filesize: Unknown

Multipath pulse shapes with refraction. NURC-FR-2006-005. April 2006.

All long range sonars have to contend with the effects of multipath propagation. One effect is that an impulse from a remote source or a reflected impulse from a point-like target will be significantly broadened. For example, in isovelocity water it has already been shown that one expects the tail of the pulse to fall off linearly in dBs with a decay constant that depends only on the bottom reflection properties and does not depend on the range of the target. Furthermore if neither sonar nor target have significant vertical directionality then the pulse shape is independent of their properties too. This finding has important implications for the design of sonars since integration times need to be matched to the characteristic arrivals of a target in its environment. The benefit of analytical solutions is that behaviour becomes immediately clear without having to cover an ndimensional parameter space. In addition one can make generalisations which would otherwise be impossible. This report extends the work to investigate the effects of upward or downward refraction. The known angle behaviour of the multipath arrivals can be converted into a time dependence to reveal the multipath pulse shape for a remote source (one-way path) or a target (two-way path). Exact solutions can be calculated numerically, explicit closed-form approximations are given for oneway paths, and these are converted to two-way paths by numerical convolution.

Multistatic active sonar system interoperability, data fusion, and measures of performance Multistatic active sonar system interoperability, data fusion, and measures of performance

Date added: 04/01/2006
Date modified: 06/22/2012
Filesize: Unknown

Multistatic active sonar system interoperability, data fusion, and measures of performance. NURC-FR-2006-004. April 2006.

Anti-submarine warfare operations are increasingly challenged due to the quiet nature of current threat submarines, and the complexity of shallow water acoustic environments in which they must be conducted. Active sonar systems have become an important addition to passive systems in the detection of submarines under such conditions. However, active sonar systems must be able to overcome unfavorable propagation conditions, high levels of obscuring reverberation, and increases in the amount of confusing target-like false alarm clutter. Multistatic active sonar configurations have been proposed as a way to augment ASW capability over standalone monostatic active sonar. Over the past several years, the NATO Undersea Research Centre and its collaborators have been engaged in conducting research into the multistatic active sonar system concept. Several at-sea multistatic research trials have been conducted and much knowledge has been gained into the system concept’s performance, interoperability requirements, potential for effective data fusion, and measures of performance. This has resulted in significant number of detailed technical reports and papers on various aspects of the subject. This work is summarized, with an extensive listing of references provided for the reader who requires more detailed treatment of the subject or wishes to obtain specific real world examples based on recent multistatics experiments conducted at sea.

The Multi-Scale multi-model Super-Ensemble cocktail: break, shake and mix The Multi-Scale multi-model Super-Ensemble cocktail: break, shake and mix

Date added: 04/01/2006
Date modified: 06/22/2012
Filesize: Unknown

The Multi-Scale multi-model Super-Ensemble cocktail: break, shake and mix . NURC-FR-2006-009. April 2006.

Nowadays, an increasing number of models are routinely providing weather forecasts and climate predictions, offering multiple options on resolutions, range domains and derived fields. On the other hand, NATO requirements are based on one scene-one forecast strategies for operational planning, complemented by small scale, short period environmental forecasts and analysis for tactical support. This fact poses two fundamental problems: from the multiple available forecasts which one should be used; and what is the accuracy and reliability of the products used for tactical support. These issues become more challenging and relevant when considering support for Expeditionary Warfare (in remote areas with limited access) and countering naval asymmetric warfare (need for high accuracy and reliability). The multi-model Super-Ensemble (SE) technique which uses an optimised combination of an ensemble of models has previously been demonstrated to improve forecast skills in atmospheric and ocean models over simple - and bias-removed - ensemble means, further improved using dynamic, regularization, non-linear or probabilistic techniques. A significant drawback of this method for systems which have specific peak frequencies, like well identified geophysical processes for example, is that it does not allow a process-wise combination of models, i.e. the weight on a model is constant whatever the process. Here we show that, by decomposing the individual models into their most relevant spectral bands and re-combining them carefully, this Multi-Scale multi-model Super-ensemble (MSSE) approach outperforms traditional SE forecast skills and allows recovering high frequency phenomena usually averaged out by SE, which offers potential new improvement in atmospheric and oceanographic modelling, uncertainty estimation and data fusion.

Scattering from axially symmetric objects: theory, FEMLAB model implementation and results Scattering from axially symmetric objects: theory, FEMLAB model implementation and results

Date added: 04/01/2006
Date modified: 06/22/2012
Filesize: Unknown

Scattering from axially symmetric objects: theory, FEMLAB model implementation and results. NURC-FR-2006-010. April 2006.

The areas of operational relevance addressed by this report are proud and buried target detection and classification. Low frequency SONAR techniques, in the range below 50 kHz for typical mine like objects, have the potential of improving the detection and classification of buried and proud targets. The advantage associated with the low frequencies is that such signals can penetrate the outer shell of the illuminated target, and interact with its interior structure. Hence, low frequency echoes can be used to detect acoustically the presence of explosive inside a target, such as for example a mine or an improvised explosive device. The penetration of low frequency sound into the sediment makes it also possible to obtain echoes from completely buried targets. A fundamental disadvantage associated with the low frequencies is that the spatial resolution is too low to make imaging-like classification possible. For this reason, it is necessary to devise physics-based processing techniques, which can aid in the detection and classification of low frequency echoes. To develop such techniques, it is necessary to rely on a priori knowledge of the low frequency echo structure. Such knowledge can come from numerical simulations or from experimental data. On the other hand, particularly the initial phases of such a research require the availability of reliable target echo models, so that it becomes possible to conduct broadband studies for a variety of different targets, in an affordable amount of time. A numerically efficient modeling tool for the computation of echoes scattered by axially symmetric targets with internal structure is presented. This report presents the mathematical formulation on which the tool is based, implementation instructions, and verified numerical results.

Calibration of cardioid beamforming algorithms Calibration of cardioid beamforming algorithms

Date added: 05/01/2006
Date modified: 06/22/2012
Filesize: Unknown

Calibration of cardioid beamforming algorithms. NURC-FR-2006-003. May 2006.

Many nations are now using or considering cardioid towed arrays as their principle receive array in active low frequency sonar applications.A drawback of cardioid array beamforming is that it is not obvious how the obtained signal levels, after processing, relate to the hydrophone pressure level. Calibrated signal levels are important, for example, for the comparison of processed cardioid data with sonar model predictions or to measure the difference in performance between cardioid arrays and line arrays. In this report mathematical expressions are derived that allow, in the case of CW or LFM signals, calibration of the cardioid processed data. The validity of these expressions is demonstrated with simulated and real active sonar data.

User Login