Browsing by Subject "Low frequency acoustics"
Now showing items 1-20 of 26
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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 ... -
Analysis of basin backscattering in the Levantine Sea
(NATO. SACLANTCEN, 1989/12)Research has been conducted in the Levantine Sea basin to measure low-frequency basin reverberation and relate the measurements to backscattering strength. The receivers were a towed horizontal array and a suspended vertical ... -
Analysis of Swallow float data at SACLANTCEN: Software notes for future use and developments
(NATO. SACLANTCEN, 1996/02)A Swallow float is as a neutrally buoyant, freely drifting unit which is deployed in deep water, equipped with one pressure sensor (hydrophone) and three orthogonal particle velocity sensors (geophones) to measure acoustic ... -
Application of ray tracing with horizontal gradient to monostatic boundary reverberation
(NATO. SACLANTCEN, 1971/12)Presented is the current work being done at the Naval Research Laboratory (NRL) on the development of a series of computer programs to predict long range, low frequency, monostatic boundary reverberation. The emphasis is ... -
Beam spreading and loss of spatial coherence in an inhomogeneous and fluctuating ocean
(NATO. SACLANTCEN, 1975/10)A theory has been developed that enables estimates to be made of beam bending, beam spreading and loss of spatial coherence. In this paper we concentrate on the loss of spatial coherence due to scattering. Using a minus ... -
Bottom time spread and bistatic scattering by rough basalt
(NATO. SACLANTCEN, 1993/08)Scattering from oceanic basalt affects low-frequency active sonar systems in at least two important ways: (1) Significant time, angle and frequency spreading reduces target echo levels when systems over-resolve the spread; ... -
Directional measurements of low-frequency acoustic backscattering from the seafloor
(NATO. SACLANTCEN, 1986/06)Long-range, low-frequency directional measurements of acoustic backscattering from the seafloor were made in the Tyrrhenian Sea using explosi ve sound sources. The signals were received by a horizontal towed array of ... -
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 ... -
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 . ... -
Low frequency active sonar: a NATO Conference held by SACLANTCEN on 24-28 May 1993 - collection of unclassified papers - volume 1 of 2
(NATO. SACLANTCEN, 1993/08)A conference on Low Frequency Active Sonar was held at SACLANTCEN from 24th to 28th May 1993. The conference was attended by over 100 delegates from NATO countries, and the topics presented ranged from environmental aspects, ... -
Low frequency active sonar: a NATO Conference held by SACLANTCEN on 24-28 May 1993 - collection of unclassified papers - volume 2 of 2
(NATO. SACLANTCEN, 1993/08)A conference on Low Frequency Active Sonar was held at SACLANTCEN from 24th to 28th May 1993. The conference was attended by over 100 delegates from NATO countries, and the topics presented ranged from environmental aspects, ... -
Low-frequency acoustic measurements in a shallow-water area with a rough sea surface
(NATO. SACLANTCEN, 1975/10)Surface wave spectra have been measured in the North Sea simultaneously with acoustic investigations using explosive and CW sources. The goal of these experiments was to determine the influence of surface waves to low-frequency ... -
Low-frequency ambient noise in the deep sound channel: the missing component
(NATO. SACLANTCEN, 1981/07)There is an important component of the undersea ambient noise which has generally been overlooked or ignored. It is the noise which arrives at a sensor, located in a deep sound channel, by way of ducted sound propagation. ... -
Medium-induced low-frequency fluctuations in acoustic transmission loss: examples from measurements in selected geographical areas
(NATO. SACLANTCEN, 1986/06)The ocean is a complex, highly variable acoustic nedium. A propagating acoustic signal is affected by a host of phenomena, including the sea-surf ace and bottom, volume inhomogenei ties, internal waves and tides, and ... -
Ocean-bottom reflectivity (a point of view)
(NATO. SACLANTCEN, 1975/10)The analysis procedures for extracting bottom loss values from pulsed acoustic signals that have interacted with the ocean bottom do not inherently consider sub-bottom refraction and reflection of sound, which are important ... -
On the physics and design of electrical discharge sources for active undersea surveillance
(NATO. SACLANTCEN, 1993/08)Underwater electrical arcs have long been used as an impulsive sound source, although efforts to improve efficiency and control acoustic output have been limited by inadequate understanding of the arc initiation process. ... -
On the recording of low frequency signals on magnetic tape
(NATO. SACLANTCEN, 1962/01)A short review of the different methods of recording on magnetic tape is given together with the advantages and disadvantages of each method. Particular emphasis was given to the ability to record low frequencies. This ... -
Reduction of low frequency active sonar clutter through image processing
(NATO. SACLANTCEN, 1997/12)Large numbers of false clutter detections arise in the use of low frequency active sonar for the detection of low Doppler submarine targets in shallow water. Traditional detection algorithms operate individually on each ... -
Refraction of sound in the sea floor
(NATO. SACLANTCEN, 1975/10)A major mode of propagation of acoustic energy at low frequencies is a shallow refracted path through unconsolidated sediments of the sea floor. Successful modelling of the bottom-refracted mode of propagation requires ... -
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 ...