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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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Experimental determination of seabed scattering law and environmental parameters from reverberation Experimental determination of seabed scattering law and environmental parameters from reverberation

Date added: 02/01/2005
Date modified: 08/14/2012
Filesize: Unknown

Experimental determination of seabed scattering law and environmental parameters from reverberation. SR-403. February 2005.

Simple theory shows that one can extract the scattering law angle dependence from ratio of reverberation to one-way propagation intensity measured on a vertical array (VLA). An experiment was carried out during BOUNDARY2003 and repeated during BOUNDARY2004 using an FM sweep as sound source first to measure vertical angle-dependent monostatic reverberation then to measure angle-dependent propagation loss as the ship mounted source moved away from the VLA. Both scattering and reflection properties are deduced in several ways without the need for modelling.

NC3A-NURC joint trials of the SkyWAN Satcom TDMA system NC3A-NURC joint trials of the SkyWAN Satcom TDMA system

Date added: 02/01/2005
Date modified: 08/14/2012
Filesize: Unknown

NC3A-NURC joint trials of the SkyWAN Satcom TDMA system. Olivier Gauvry; Marian Machalica; André Terrasse; Alessandro Berni; Michel Leonard; Diego Merani. SR-407. February 2005.

The report documents the trials conducted by NURC and NC3A in spring 2004. Trials were to assess the real time performance of a Satcom TDMA mechanism called SkyWAN in conjunction with end-to-end IP applications. That mechanism is currently used by NURC to support its operational communication links with its two NATO research vessels when at sea. In order not to disturb these operational links, NURC negotiated with Eutelsat additional Satcom bandwidth to support those experimental trials. The major points of interest reported in that note are the description of the NURC VSAT characteristics, the configuration architecture and setting related to the NURC-NC3A trials, the basic end to end performance and a preliminary conclusion on the use of the SkyWAN mechanism.

Performance modelling and validation for distributed multistatic tracking Performance modelling and validation for distributed multistatic tracking

Date added: 02/01/2005
Date modified: 08/14/2012
Filesize: Unknown

Performance modelling and validation for distributed multistatic tracking. Coraluppi, S. SR-397. February 2005.

This report develops a distributed multi-sensor tracker performance model that accounts for the target fading effect that we observe in sea trial data. We study model-based performance as a function of key tracker parameters, the choice of tracker architecture, and the number of distributed sensors. We validate the fidelity of the model by comparing model-based performance with actual tracker performance based on simulated contact data

Seabed characterization by inversion of acoustic propagation and reverberation data received on a towed horizontal array Seabed characterization by inversion of acoustic propagation and reverberation data received on a towed horizontal array

Date added: 02/01/2005
Date modified: 08/14/2012
Filesize: Unknown

Seabed characterization by inversion of acoustic propagation and reverberation data received on a towed horizontal array. Nielsen, Peter L. ; Fallat, Mark ; Marconi, Valter. SR-417. February 2005.

Sonar performance prediction in shallow-water is highly dependent on the char-acteristics of the underwater environment. The bottom properties are critical input parameters to prediction tools and these parameters are probably the most dicult to estimate. Inversion of measured acoustic signals (direct propagation and diffuse reverberation) provides a technique to infer these bottom parameters. An ad-hoc approach using the sensors of the sonar system is proposed where the local geoacoustic properties are determined by inverting the data received on a horizontal array. The local geoacoustic properties are used as initial or guidance inputs to a reverberation model to estimate range-averaged geoacoustic and scattering properties from long-range reverberation data.

Using a vertical line array and ambient noise to obtain measurements of seafloor reflection loss Using a vertical line array and ambient noise to obtain measurements of seafloor reflection loss

Date added: 03/01/2005
Date modified: 08/14/2012
Filesize: Unknown

Using a vertical line array and ambient noise to obtain measurements of seafloor reflection loss. Victor Young. SR-410. March 2005.

Bottom reflection properties can be obtained from ambient noise directionality. The results obtained at six sites in 2002 with NURC’S 62m VLA are summarised. At four of the sites the VLA was moored, in order to study a single seafloor environment, while at the other two sites the VLA was allowed to drift, in order to study geographical changes in the seafloor environment. Several variants of the measurement and processing techniques are investigated here. Firstly, rather than using only the uniformly spaced central section of a nested vertical array (VLA), one can expand the useful size of the array to about three quarters (rather than one half) of the full array length by padding out the array’s correlation matrix. The padding makes the apparently good assumption that the noise crossspectral-density matrix is Toeplitz. Thus the initially sparse matrix for the outer sections of the array (with wider hydrophone separations) can be filled out with values from elsewhere in the true matrix. This provides better angular resolution which is beneficial for the method. Secondly, the possibility of synthesising a VLA with a pair of hydrophones is investigated. The benefit of a synthetic aperture would be the lower cost of the equipment in an operational context. For the process to work (without extremely long integration times) the noise source spatial distribution needs to be stationary.

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