Reprints: Recent submissions
Now showing items 461-480 of 548
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Different approaches to economic cruising speeds on a CODOG frigate with due regard to radiated noise
(NATO. SACLANTCEN, 1985/01)All navies, in recent years, have been much more concerned in economic cruising speeds of ships. Frigate type naval ships are usually characterized by two shafts, by multiple propulsion engines per shaft, and by different ... -
The seamount as a noise barrier
(NATO. SACLANTCEN, 1982/06)When the path from a localized noise source is intercepted by a seamount the shielded noise consists of a diffracted component and, if the seamount is close to a sufficiently smooth ocean surface , a multiply-reflected ... -
Effects of topographic blockage and ocean boundaries on low frequency noise fields
(NATO. SACLANTCEN, 1982/06)Low frequency noise in most ocean areas is dominated by shipping or industrial noise. The composite noise field is the result of radiated energy from each discrete noise source propagating over relatively large distances ... -
The prediction of temporal statistics of directional ambient shipping noise
(NATO. SACLANTCEN, 1982/06)A technique for predicting the probability density function (PDF) of the ambient-noise power received by a narrow-band system in a modelled shipping and wind noise field is described. The densities of the shipping noise ... -
Site dependence of wind-dominated ambient noise in shallow water
(NATO. SACLANTCEN, 1982/06)A survey of ambient noise data in shallow water taken under wind-dominated conditions shows substantial differences in spectrum level (often greater than 10 dB) under the same windspeerl and sea-state conditions. This ... -
Site and frequency dependence of ambient noise in the North Eastern Pacific Ocean
(NATO. SACLANTCEN, 1982/06)One-hour averages of omnidirectional ambient noise measurements at 60 Hz and 165 Hz are analyzed for two nearby, deep ocean sites in the Northeastern Pacific during February and March 1981. Site A is a high noise site and ... -
An experimental verification of a geometric acoustic approximation
(NATO. SACLANTCEN, 1971/12)This paper sets out to show that a very simple ray treatment may be used to give a surprisingly good estimate of a sound field, even in conditions where the criteria for the use of geometric acoustics are apparently not fulfilled. -
Detection models and target information processing
(NATO. SACLANTCEN, 1982/06)The passive sonar equation leads in a natural manner to sensor detection performance contours. Useful information can be extracted from observed fractional holding time on non-cooperative targets by use of these contours. ... -
Is power averaging the best estimator for undersea acoustic data?
(NATO. SACLANTCEN, 1982/06)The power average is the statistic which is commonly used in all types of acoustic data processing. It is an excellent estimator for "well behaved" Gaussian distributions when the central or average value is desired. ... -
A parametric examination of some properties of the low-frequency ambient noise field
(NATO. SACLANTCEN, 1982/06)Models for ship-generated ambient noise vary considerably in the detail required of their input data on sources and the environment. This paper describes a model that predicts ambient-noise levels and cumulative distribution ... -
Optimal detection and tracking of acoustical noise sources in a time-varying environment
(NATO. SACLANTCEN, 1982/06)A dynamical detector estimator is derived for nonlinear nongaussian signal processes based on Bucy's representation theorem which is the fundamental result in stochastic filtering. A quantized version of two-dimensional ... -
Performance of three averaging methods for various distributions
(NATO. SACLANTCEN, 1982/06)The performance of three averaging methods, namely the sample median, the sample arithmetic mean, and the sample geometric mean, are analyzed in tenns of their bias, variance, and mean square error. The bias and variance ... -
Influence of background-noise spatial coherence on high-resolution passive method
(NATO. SACLANTCEN, 1982/06)New signal processing methods for passive listening have appeared recently : they are called "high resolution" methods because they have theoretically a better resolving power than conventional or adaptive beamforming . ... -
A method of estimating the influence of ship's noise on ambient noise measurements
(NATO. SACLANTCEN, 1982/06)Ambient noise measurements are often adversely affected by noise from passing ships. Here, a method is presented which allows the estimation of this influence. The method is especially suitable for shallow water applications. ... -
Notes on the interpretation of ambient noise statistics
(NATO. SACLANTCEN, 1982/06)Interpretation of statements about the character of ambient sea noise, as well as schemes to measure or model noise, are sensitive to the context or underlying view of what is essentially a stochastic process. A framework ... -
Ambient noise levels in the Northeast Pacific ocean as measured by aircraft-dropped sonobuoys
(NATO. SACLANTCEN, 1982/06)Ambient noise measurements obtained from sonobuoys air-dropped by U.S.Navy P-3 aircraft during operations over the northeastern Pacific Ocean from January 1978 to December 1980 have been analysed for spatial and temporal ... -
Acoustic ambient noise in the Barents Sea
(NATO. SACLANTCEN, 1982/06)Recorded observations of acoustic ambient noise in the Western Barents Sea are presented. The observations were made in a position approximately 100 km North of North Cape in Norway, with the hydrophone on the bottom - ... -
Depth dependence of directionality of ambient noise in the North Pacific: experimental data and equipment design
(NATO. SACLANTCEN, 1982/06)Ambient ocean noise studies have been part of the research program of the Marine Physical Lab (MPL) for many years. In recent years this work has included several studies of the depth dependence of vertical directionality ... -
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 ... -
Experimental data on the refraction of underwater explosion pulses
(NATO. SACLANTCEN, 1971/12)There are several reasons why a researcher in underwater acoustics might be interested in the use of explosion pulses as sources. The most generally recognized reason is that explosions are convenient and powerful sources ...