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Now showing items 221-240 of 882
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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 ... -
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 ... -
Seismic and hydroacoustic sensing of infrasonic noise in coastal waters
(NATO. SACLANTCEN, 1982/06)Three-component ocean-bottom seismometers with radio links have been deployed in coastal waters to investigate natural and man-made noise at extremely low frequencies. Seismograms from one or up to three sensor stations ... -
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 ... -
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 ... -
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 - ... -
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. ... -
Low-frequency seismic and hydroacustic noise measurements in a fjord
(NATO. SACLANTCEN, 1982/06)Low frequency ambient noise signals from an ocean bottom seismometer (oBS) put on the sea floor of a Norwegian fjord have been studied. The instrument contains 3 seismometers and one hydrophone, and signals from all 4 ... -
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. ... -
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 ... -
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 ... -
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 ... -
Flow noise interference in measurements of infrasonic ambient noise
(NATO. SACLANTCEN, 1982/06)Estimates are presented of the local noise generated at infrasonic frequencies by turbulent water flowing in the vicinity of hydrophones used for measurements of ambient noise in the sea. Three situations are discussed: a ... -
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 ... -
Role of propagation in ambient noise
(NATO. SACLANTCEN, 1982/06)To be useful for modern ASW systems design and analyses, descriptions of ambient noise fields must go beyond average omnidirectional spectra and include horizontal and vertical patterns, fluctuations with time, dependencies ... -
Acoustic source characteristics of merchant ships
(NATO. SACLANTCEN, 1982/06)Merchant ships are sources of broadband acoustic noise which can interfere with and confuse ocean surveillance. The purpose of this discussion is to review: the status of research on and measurements of merchant ship ... -
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 ... -
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 ...