Browsing by Type "Papers and Articles"
Now showing items 2140 of 562

A noise directionality model including variable bathymetry
(NATO. SACLANTCEN, 1997)In this paper we investigate the noise directionality due to distributed surface sources m several envtronments with a uniformly sloping sea bed. Of particular interest are frequency dependence and the question of the ... 
A novel approach for a bistatic scattering calculation suitable for sonar performance model
(CMRE, 2014/01)One of the classical approaches to the calculation of the sound pressure scattered from a rough surface is to sum the contributions to the field from a set of small tiles that approximate the surface. If the tiles are ... 
A novel method to enlarge the scanning region of a focused beamformer
(NATO. SACLANTCEN, 1997)Often focused beamforming systems use the Fresnel approximation to compute the required delays. Unfortunately, such an approximation has a validity region that is very narrow around the broadside direction. To investrgate ... 
A parametric examination of some properties of the lowfrequency ambient noise field
(NATO. SACLANTCEN, 1982/06)Models for shipgenerated ambient noise vary considerably in the detail required of their input data on sources and the environment. This paper describes a model that predicts ambientnoise levels and cumulative distribution ... 
A PC/Linux software toolkit for coastal swath mapping
(NATO. SACLANTCEN, 1997)Assembly of a PC/Linux based data acquisirion and processing software toolkit for coastal (shallow water) multibeam and sidescan swath mapping sonar systems has been undertaken by the URI Ocean Mapping Development center ... 
A planewave decomposition method for modeling scattering from objects and bathymetry in a waveguide
(NATO. SACLANTCEN, 1996/11)In this paper a straightforward planewave decomposition method which can be used for solving object andlor interface scattering problems in a waveguide is described. The method utilizes the freespace scattering matrix ... 
A real time system for towed array calibration and performance analysis, or how to get 50 dB sidelobes from a towed array
(NATO. SACLANTCEN, 1982/06)Sidelobe suppression levels of 30 dB for a towed array are generally considered excellent; values above that are considered exceptional or unachievable. However, 40 t o 50 dB suppression levels have been achieved and ... 
A relation between multipath group velocity, mode number, and ray cycle distance
(CMRE, 2014/01)Weston's ray invariant or "characteristic time" in a rangedependent environment is exactly equivalent to the WentzelKramersBrillouin phase integral for ducted normal modes. By considering a ray element it is shown that ... 
A review of oceanic fronts
(NATO. SACLANTCEN, 1975/10)This paper will start with a brief account of oceanic frontal research. The definition of oceanic and acoustic fronts and the distinction between them will be discussed. Examples of frontal structure dynamics, correlation ... 
A review of some developments in ray tracing at the Naval Air Development Center
(NATO. SACLANTCEN, 1971/12)The Naval Air Development Center has a comprehensive raytracing program which has been extensively used for a number of years not only by our own laboratory, but also by other naval activities and private contractors . ... 
A shallow water system for maximizing echo to reverberation ratio
(NATO. SACLANTCEN, 1993/08)A method for increasing incident energy on middepth targets while at the same range reducing boundary reverberation for shallow water ducts has been devised. The basis of the approach is couched in range dependant normal ... 
A solution of of the wave sound equation in shallow water for real speed profiles and solid bottom under sediment
(NATO. SACLANTCEN, 1975/10)The wave equation has been solved by using normal mode theory. The medium is assumed to be horizontally stratified. A closed form solution has been found in the case of GANS  PEDERSEN types of density and soundspeed ... 
A spectral ocean wave model
(NATO. SACLANTCEN, 1975/10)An operational wave spectral model has been developed through the cooperative efforts of FLENUMWEACEN, NAVOCEANO and W.J. Pierson. The model contains two subdivisions: 1) wave energy growth based on a modified version of ... 
A study of the turbulent flow and character of the water masses over the Sicilian ridge in both summer and winter
(NATO. SACLANTCEN, 1972/09)The western sill region of the Strait of Sicily lies between Sicily (Capo Lilibeo) and Tunisia (Cap Bon) and is part of the submarine ridge separating the eastern from the western Mediterranean. [Fig. lJ. It was studied ... 
A summary of oceanographic data obtained in deep water in the Strait of Sicily in May 1970: MILOCMED surv 70
(NATO. SACLANTCEN, 1972/09)Observations of temperature and salinity using a TSD profiling system were made down to 500 m in a deep water area southeast of Pantelleria Island in the Strait of Sicily in May, 1970. The usual two layer system was observed, ... 
A survey of practical considerations relative to the processing and analysis of underwater acoustic signals
(NATO. SACLANTCEN, 1972/05)An investigation, aimed at bringing into sharper focus · tb~ strong interrelationships that exist between the measurement, p r o c essing, and analysis of underwater acoustic signals, is conducted. Emphasis is on practical ... 
A technique of comparative analysis of underwater sound transmission loss curves
(NATO. SACLANTCEN, 1975/10)A procedure has been developed for the analysis of transmission loss curves in which received power is known or expressible as a linear function of range. The procedure separates each curve into a sum of three components ... 
A theoretical method for the prediction of underwater explosion pulses at caustics
(NATO. SACLANTCEN, 1971/12)Our concern [Refs. 1 and 2J is with the effect of refraction on the long range propagation of underwater explosion shock waves. Here, as with acoustic sources, ray tracing can be used to predict refraction effects. From ... 
A theoretical model for doppler spread of backscattered sound from a composite roughness sea surface
(NATO. SACLANTCEN, 1975/10)For calculating the Doppler spread of acoustical reverberation from the sea surface, good results are achieved by applying a compositeroughness model. The small wavelets primarily responsible for the backscattering are ... 
A theoretical model for the backscattering strength of a composite roughness seasurface
(NATO. SACLANTCEN, 1974/02)The surfacebackscattering strength is calculated according to Rayleigh theory for surface excursions much smaller than the sound wavelength. By taking into account of selfshadowing and modulation of grazing angles, the ...