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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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Simultaneous inversion of propagation and reverberation data Simultaneous inversion of propagation and reverberation data

Date added: 12/01/2006
Date modified: 06/22/2012
Filesize: Unknown

Simultaneous inversion of propagation and reverberation data. NURC-FR-2006-023. December 2006.

This report describes progress in a methodology to in situ extract bottom geoacoustic and scattering properties for integration in advanced low-frequency environmentally adaptive sonar systems. The environmental characterization technique is based on inversion of short-range acoustic propagation and long- range reverberation data acquired on the sonar system itself. The documented results show significant improvement in reliability of the extracted bottom properties by inverting propagation and reverberation data simultaneously. Further, there is good agreement between the inversion results and alternative measure- ments of "ground truth" bottom characteristics acquired during sea trials.

Sea surface temperature sensitivity of an ocean-atmosphere coupled system to the parameterization of boundary layer clouds Sea surface temperature sensitivity of an ocean-atmosphere coupled system to the parameterization of boundary layer clouds

Date added: 12/01/2006
Date modified: 08/13/2012
Filesize: Unknown

Sea surface temperature sensitivity of an ocean-atmosphere coupled system to the parameterization of boundary layer clouds. Teixeira, J. ; May, P. ; Flatau, F. ; Hogan, T.F. NURC-FR-2006-024. December 2006.

In this paper we report on the impact of a more realistic low-cloud cover parameterization on the Sea Surface Temperature (SST) predicted by an ocean atmosphere coupled system. In particular, it is shown that the atmospheric model with more realistic boundary layer clouds leads to a more realistic distribution of the SST in the ocean’s tropics, subtropics and mid-latitudes. Typical SST biases of up to 5 C in regions under frequently observed stratus and stratocumulus are substantially reduced, to unbiased values at places. This represents a substantial SST forecast improvement in terms of operational coupled systems used in the context of Maritime Rapid Environmental Assessment (MREA).

Advances in the multistatic tactical planning aid Advances in the multistatic tactical planning aid

Date added: 12/01/2006
Date modified: 06/22/2012
Filesize: Unknown

Advances in the multistatic tactical planning aid. NURC-FR-2006-022. December 2006.

This report describes the progress made to date on modelling multistatic ASW operations for tactics development focusing specifically on the multistatic acoustic system. The main result of the work described here is the production of the core modules for a tool to analyse multistatic sonar employments. These modules consist of a low frequency active multistatic sonar performance model for target detections, a tracker-fusion module for tracking detections, a simulation of realistic false contacts, a communications network module for the sharing of information between the assets and an embryonic model of an ASW operator in the task of classifying target tracks. In addition a Monte-Carlo simulation module was produced for the systematic analysis of multistatic ASW operations and the structure for future development.

Characterization of local seabed properties using synthesized horizontal array data Characterization of local seabed properties using synthesized horizontal array data

Date added: 01/01/2007
Date modified: 06/22/2012
Filesize: Unknown

Characterization of local seabed properties using synthesized horizontal array data. NURC-FR-2007-001. January 2007.

In April 2002 NURC conducted the BOUNDARY 2002 experiment on the Malta Plateau, Mediterranean Sea, with the aim of collecting high-quality environmental and acoustic data. A part of these data was directly intended for geoacoustic inversion characterizing the bottom properties by acoustic measurements. The acoustic data were collected by using towed sources covering a frequency band 180-7000Hz and received on a bottom- moored vertical array. The sources were towed about 1 km on both sides of the array and passing the shallowest hydrophone at a range of 21m. The transmission rate was every 3 s resulting in high spatial sampling of the acoustic field. The high repetition rate of the transmissions provide the possibility of building a 1-km synthetic horizontal array with a virtual hydrophone spacing of about 5.9m. The principle of reciprocity, i.e. interchanging the source and receiver positions, is applied to build the synthetic horizontal array. The acoustic data collected from this synthetic horizontal array are used to characterize the bottom properties locally by matched-field geoacoustic inversion and to extract the reflection coefficient from a spherical wave interacting with the bottom. The reflection coefficient is calculated by time-gating of the direct and bot tom arrivals of the matched-filtered signal. The results from the inversion are compared with independent “ground truth” data collected at the experimental site. Both the matched-field inversion and the determination of the reflection co efficient are strong candidates for rapid characterization of bottom properties locally over large areas. This implies the use of fast and agile platforms like Autonomous Underwater Vehicles with broad-band sound sources and arrays and eventually a supporting sono-buoy field.

A method for sea floor clutter suppression in side scan sonar images A method for sea floor clutter suppression in side scan sonar images

Date added: 02/01/2007
Date modified: 06/22/2012
Filesize: Unknown

A method for sea floor clutter suppression in side scan sonar images. R. Grasso, F. Spina. NURC-FR-2007-002. February 2007.

A clutter suppression algorithm for improving detection of unknown spatially distributed small targets on a textured sea floor background in side scan sonar images is analysed and tested. The algorithm is based on a multi-resolution transform of the sonar data and a projection pursuit (PP) algorithm, which is used to enhance signal-to-clutter ratio in the multi-resolution space. The sea floor background in a sub-image is modelled by a set of texture features estimated from the image data by a two dimensional un-decimated wavelet transform. Each image sample is associated with a vector of features which are composed by the local mean energy resulting from a bank of multi-resolution oriented bandpass filters. The target points in the feature space appear as a small set of outliers compared to the feature vector distribution of the background. The feature vector data set is projected, by a PP algorithm, along the direction of kurtosis maximisation of the data which is sensitive to the outliers in a data set. The projected signal is used in a threshold test for detecting anomalies in sea floor background signals. An ad hoc gradient algorithm to maximise the kurtosis iteratively was studied and developed. An efficient procedure to find a first guess solution to initialise the gradient algorithm was proposed and tested on a side scan sonar data set acquired during the NURC BP02 cruise by a ship towed sensor. The improvement in the signal-to-clutter ratio observed in this case ranges between 5 and 8 dB.

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