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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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Effects of source and receiver positional offsets in multistatic range determination Effects of source and receiver positional offsets in multistatic range determination

Date added: 07/01/2005
Date modified: 08/14/2012
Filesize: Unknown

Effects of source and receiver positional offsets in multistatic range determination. SM-432. July 2005.

During the Adults’03 sea trial (a joint research project between NATO URC and TNO-FEL, The Netherlands) a number of experiments were conducted to investigate the effects of equipment offsets in multistatic range determination. The analysis presented in this report is based on data collected during experiment P02b where the two participant ships, both towing an LFAS source-receiver pair, were arranged into an in-line configuration and proceeded with same speed and heading. The direct blast arrivals are used to acoustically calculate the distance between sources and receivers. The comparison between the expected arrival times (according to the geometry) and the measured arrival times gives an indication on how equipment offsets, latencies, positional errors and unknown sound speed effect range determination.

Effects of the internal waves on the acoustic propagation Effects of the internal waves on the acoustic propagation

Date added: 07/01/2005
Date modified: 08/14/2012
Filesize: Unknown

Effects of the internal waves on the acoustic propagation. SM-433. July 2005.

A simple 2D model called SOFIA has been developed in order to predict sound-speed fluctuations in the water column due to linear internal waves. It is based on solving the equation governing the vertical particle velocity associated with the internal waves, using a modal decomposition of the internal wave field. The main feature of the model is the use of experimental data: the Brunt-Väisälä profile is calculated from the density profile registered by the CTD cast, the amplitudes of the normal modes are determined using ADCP data and the spectrum is deduced from the thermistor chain measurements. The effects of the linear internal waves on the acoustic propagation were studied through several numerical simulations using some sound-speed profiles predicted with the SOFIA model. The acoustic simulations were performed with the REVPA model, based on a wide-angle approximation of the parabolic equation (PE) method. Through these simulations, the possible relation between the influence of the internal waves and different values of the environmental parameters was assessed. The environmental parameters considered in this study were the source depth, the acoustic frequency and the sediment properties.

Manual of BORIS-SSA: Bottom Response from Inhomogeneities and Surface using the Small-Slope Approximation, version 1.0 Manual of BORIS-SSA: Bottom Response from Inhomogeneities and Surface using the Small-Slope Approximation, version 1.0

Date added: 07/01/2005
Date modified: 08/14/2012
Filesize: Unknown

Manual of BORIS-SSA: Bottom Response from Inhomogeneities and Surface using the Small-Slope Approximation, Version 1.01. M-152. July 2005.

The description of a software tool capable of simulating, in the time domain, the acoustic time series resulting from scattering from various seafloor types and acoustic source/receiver geometries is presented in the form of a user manual. This package, named BORIS-SSA, is an upgrade, with various new features, of BORIS-3D. The parameters of the model characterize the sonar directivity and pulse shape, the geometrical configuration of the scattering problem and the geo-physical characteristics of the seafloor (but also sea surface or other surface). This surface can be generated to have various statistical behaviours or can be obtained from deterministic data based on the surface heights (profilometry, stereo-photogrammetry, bathymetry, etc). The package is platform independent and user friendly. This report is intended as a detailed description of the implementation on a source code level. A short introduction to the model underlying the package and a comprehensive demonstration program are also given.

Near normal classification of the upper layer of the seabed Near normal classification of the upper layer of the seabed

Date added: 07/01/2005
Date modified: 08/14/2012
Filesize: Unknown

Near normal classification of the upper layer of the seabed. Pouliquen, E. SM-421. July 2005.

Acoustic time series acquired at normal incidence from typical echosounders are highly dependent on the distance (also called "depth") between the transducer and the mean seabed level. As several classification systems use the seabed signal shape and energy, its depth dependence needs to be compensated for before processing. Without depth correction, a bias in the classification and inversion procedure is introduced. This paper describes the steps required to produce quasi depth-independent echoes for a given seabed type, that reduce the bias in the classification process. The proposed method is applied to data acquired in Nova Scotia on a geo-acoustically complicated area. Variability and reliability associated to this classification process is also investigated.

Present and future in-buoy processing for the DEMUS system Present and future in-buoy processing for the DEMUS system

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

Present and future in-buoy processing for the DEMUS system. Crowe, D. Vance. NURC-MR-2006-003. August 2006.

This report discusses the DEMUS project, its history and status in 2004, and outlines options for future improvement and development. It provides a review of the DEMUS system development, discusses the current hardware in the context of other ASW sensors and shows that the DEMUS buoys have a role to play in a multi-static multi-platform environment. The report also discusses the development issues to make the buoys more useful both as a research tool for the Centre and as a multi-static ASW sensor.

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