Browsing Reprints by Title

Now showing items 336-355 of 548

    • Noise sources in the ocean - part 1 

      Wille, Peter C. (NATO. SACLANTCEN, 1975/10)
      Following a brief historical survey of the development of our knowledge of the origins and characteristics of ambient noise in the ocean, the principal known sources of noise are described. These are: environmental origin, ...

    • Noise sources in the ocean - part 2 

      Daintith, Maurice J. (NATO. SACLANTCEN, 1975/10)
      Following a brief historical survey of the development of our knowledge of the origins and characteristics of ambient noise in the ocean, the principal known sources of noise are described. These are: environmental origin, ...

    • NOSC signal processing evaluation laboratory 

      Pennoyer, Bryson (NATO. SACLANTCEN, 1979/12)
      A new acoustic Signal Processing Evaluation Laboratory (SPEL) at the Naval Ocean Systems Center (NOSC), San Diego, is described. This laboratory has been designed to support a broad program of research and development of ...

    • Notes on the interpretation of ambient noise statistics 

      Cavanagh, Raymond C. (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 ...

    • Numerical modeling results for mode propagation in a wedge 

      Jensen, Finn B.; Tindle, C. T. (NATO. SACLANTCEN, 1987/11)
      A PE (parabolic equation) code is used to study propagation in a shallow water wedge with a penetrable bottom. Particular attention is given to "wedge modes" that have wave fronts that are arcs of circles centered on the ...

    • Numerical modelling of acoustic scattering by smooth inclusions in a layered fluid-solid medium 

      Karasalo, Ilkka; Mattsson, Johan (NATO. SACLANTCEN, 1997)
      A boundary integral equation (BIE) method as descnbed for computing the scattering of a monofrequent acoustic field by a smooth, rigid 30 object in a layered range-independent fluid-solid medium. The BIE is discretized ...

    • Obtaining the ocean index of refraction spectrum from the acoustic amplitude fluctuations 

      Rouseff, Daniel; Ewart, Terry E.; Reynolds, Stephen A. (NATO. SACLANTCEN, 1997)
      The feasibility of using acoustic measurements to determine the properties of a shallow water internal wave field is investigated through numerical simulations. The random intemal wave field is modeled by a generalized ...

    • The ocean noise coherence matrix and its rank 

      Harrison, Chris H. (CMRE, 2019/05)
      An expression for the cross-spectral density matrix of ocean noise naturally separates into a Toeplitz part and a Hankel part [Harrison (2017). J. Acoust. Soc. Am. 141, 2812?2820]. The Toeplitz part is shown to be substantially ...

    • Ocean-basin reverberation from large underwater explosions: part 1: source-level and propagation-loss modelling 

      Blatstein, Ira M. (NATO. SACLANTCEN, 1975/10)
      Predicting the reverberant returns from ocean basin reflectors requires describing acoustic source levels for large, conventional underwater explosions, defining the two way propagation loss and signal spreading from the ...

    • Ocean-basin reverberation from large underwater explosions: part 2: computer model for reverberation 

      Goertner, Jean A. (NATO. SACLANTCEN, 1975/10)
      Following detonation of an underwater explosion, sound reverberates from the ocean surface and bottom and from scatterers within the medium. In addition, the boundaries of the ocean basin and obstructions within it, such ...

    • Ocean-bottom reflectivity (a point of view) 

      Santaniello, S. R.; DiNapoli, Frederick R. (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 ...

    • Oceanic layered microstructure and fronts 

      Johannessen, Ola M. (NATO. SACLANTCEN, 1971/12)
      This talk is divided into two parts: one deals with oceanic microstructure, with particular attention to the so-called "layered microstructure"; the other part is concerned with oceanic fronts. As an example of the latter ...

    • Oceanic-acoustic experiments at SACLANTCEN 

      Allan, Thomas D. (NATO. SACLANTCEN, 1971/12)
      Last year, at the Director's suggestion, a project in oceanicacoustics was set up at the Centre with scientists from at least 3 groups playing some part in the planning and execution of experiments. The p roject represents ...

    • Oceanographic field estimates from remote sensing and glider fleets 

      Alvarez, Alberto; Mourre, Baptiste (CMRE, 2014/01)
      This work investigates the merging of temperature observations from a glider fleet and remote sensing, based on a field experiment conducted in an extended coastal region offshore La Spezia, Italy, in August 2010. Functional ...

    • On adaptive modulation for low SNR underwater acoustic communications 

      Pelekanakis, Konstantinos; Cazzanti, Luca (CMRE, 2019/05)
      This paper deals with adaptive underwater acoustic (UWA) communications where the receiver must operate at low signal-to-noise ratios (SNRs). The proposed modem is equipped with a set of direct sequence spread spectrum ...

    • On adaptive underwater object detection 

      Williams, David P. (NURC, 2012/04)
      A new algorithm for the detection of underwater objects in sonar imagery is proposed. One particularly novel component of the algorithm also detects the presence of, and estimates the orientation of, sand ripples. The ...

    • On the effects of synthetic-aperture length on SAS seabed segmentation 

      Williams, David P.; Groen, Johannes (NURC, 2009/12)
      In this work, we quantify the relationship between synthetic-aperture length (or equivalently, along-track resolution) and seabed segmentation performance experimentally for real synthetic aperture sonar (SAS) imagery. The ...

    • On the integration of through-the-sensor geoacoustic inversion techniques for environmental adaptation schemes in low frequency active sonars 

      Le Gac, Jean-Claude (NURC, 2007/12)
      The environmental conditions in shallow water areas are known to strongly affect the performances of low frequency active sonars (LFAS). In particular, interactions of the acoustical field with the seabed interface have ...

    • On the physics and design of electrical discharge sources for active undersea surveillance 

      Sutton, Stephen P.; Olson, Allen H. (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 relationship between SAS image resolution and target-detection performance 

      Williams, David P.; Hunter, Alan Joseph (CMRE, 2019/06)
      The relationship between synthetic aperture sonar (SAS) image resolution and target-detection performance is quantified. It is first demonstrated how a lower-resolution SAS system can be simulated in a principled manner ...