Browsing Reprints by Title

Now showing items 465-484 of 548

    • Statistical evaluation of 80 kHz shallow-water seafloor reverberation 

      Lyons, Anthony P.; Abraham, Douglas A.; Akal, Tuncay; Guerrini, Piero (NATO. SACLANTCEN, 1997)
      In this work a comparison is presented between 80 kHz reverberation statistics obtained at shallow water sites around Sardinia and Sicily. The data include measurements from several distinct bottom provinces, including ...

    • Status of ray theory development of Naval Undersea Research and Development Center 

      Gordon, D. F. (NATO. SACLANTCEN, 1971/12)
      The first part of this paper discusses NUC (Naval Undersea Research and Development Center) work on the accuracy and validity of ray theory. By comparing the range to convergence zones as indicated by experiment and by ...

    • Stochastic methods of sound-field computation 

      Goodman, Ralph R. (NATO. SACLANTCEN, 1975/10)

    • Sub-bands beam-space adaptive beamformer for port-starboard rejection in triplet sonar arrays 

      Stinco, Pietro; Tesei, Alessandra; Maguer, Alain; Ferraioli, Fabrizio; Latini, Valerio; Pesa, Luca (CMRE, 2019/05)
      This paper addresses the problem of Port-Starboard (PS) beamforming for low-frequency active sonar (LFAS) with a triplet receiver array. The paper presents a new algorithm for sub-bands beam-space adaptive beamforming with ...

    • Subcritical penetration of narrow Gaussian beams into sediments 

      Jensen, Finn B.; Schmidt, Henrik (NATO. SACLANTCEN, 1988/03)
      Complete wave-theory solutions have been obtained numerically for both the reflected and the transmitted fields associated with a narrow Gaussian beam incident on a water-sediment interface near the critical grazing angle. ...

    • Summary and recommendations 

      Clarke, Richard H. (NATO. SACLANTCEN, 1971/12)
      An unfortunate first impression might be that ray tracing is dull, simply because the idea is a very old one. In fact, ray tracing is the single most powerful method available to us for understanding the complexities of ...

    • Supporting AUV localisation through next generation underwater acoustic networks: results from the field 

      Munafó, Andrea; Furfaro, Thomas C.; Ferri, Gabriele; Alves, João (CMRE, 2017/11)
      This work describes how the localisation of autonomous underwater vehicles can be supported through net-worked acoustic communication. The localisation approach in-cludes timing information within acoustic messages to ...

    • Surface duct propagation loss measurements and model predictions at low and mid frequencies 

      Klingbeil, Delia H. (NATO. SACLANTCEN, 1993/08)
      Side-by-side measurements of low- and mid-frequency propagation loss were obtained during a sea test conducted in the North Atlantic during February of 1992. These measurements are compared to each other and with model ...

    • Surface wave spectra 

      Crowther, P. A. (NATO. SACLANTCEN, 1975/10)
      A classification is made of the different types of wave elevation spectra namely lD time spectra, lD spatial spectra, 2D spatial spectra and 3D space-time spectra. Relations with simple single parameter measures of surface ...

    • Swath bathymetry and SAS autofocus using a Chirp source 

      Shippey, Geoffrey; Kröling, Olle (NATO. SACLANTCEN, 1997)
      Swath bathymetry and SAS autofocus can both be treated as problems in correlating echoes from a scatterer distribution on the seabed. Using a chirp source, the phase derived from quadrature match-filtering can replace the ...

    • System functional migration: high-level language to hardware 

      Wu, Y. S.; Lloyd, G. R. (NATO. SACLANTCEN, 1979/12)
      This paper intends to examine system functional allocation among available processing resources in a systematic way. The discussion will focus first on the criteria for assigning functions to processors, that is, horizontal ...

    • Tactical data acquisition experiences 

      Messere, E. L. (NATO. SACLANTCEN, 1972/05)
      The requirements of Tactical Data Acquisition systems are discussed and summarized. Experiences with equipment and their utilization are described including : quantities measured, input signal conditioning, analogue ...

    • Tank measurements of elastic scattering by a resin-filled fiberglass spherical shell 

      Tesei, Alessandra; Guerrini, Piero; Canepa, Gaetano (NURC, 2007/12)
      Acoustic elastic scattering measurements were conducted in a tank on a 6cm radius fibreglass spherical shell filled with a low-shear-speed epoxy resin. Preliminary measurements were conducted also on the void shell before ...

    • Tank measurements of scattering from a resin-filled fibreglass spherical shell with internal flaws 

      Tesei, Alessandra; Guerrini, Piero; Zampolli, Mario (NURC, 2008/09)
      This paper presents results of acoustic inversion and structural health monitoring achieved by means of low to midfrequency elastic scattering analysis of simple, curved objects, insonified in a water tank. Acoustic elastic ...

    • Target detection and location with ambient noise 

      Harrison, Chris H. (NURC, 2008/09)
      By placing a vertical array in an ambient noise field and forming an upward and a downward beam one obtains two time series which can be cross correlated to reveal a subbottom profile of the seabed [Siderius et al., J. ...

    • Target time smearing with short transmmissions and multipath propagation 

      Harrison, Chris H. (NURC, 2012/04)
      In active sonar the target echo level is often estimated with a propagation model that adds all multipath arrivals. If the (post-correlator) transmitted pulse is short compared to the multipath time spread then there is ...

    • Temporal fluctuation of backscattered field due to bioturbatioon in marine sediments 

      Jones, Christopher D.; Jackson, Darrell R. (NATO. SACLANTCEN, 1997)
      Biological activity in marine sediments creates a time-varying, randomly fluctuating medium. A bio-diffusive model is proposed for predicting the temporal and spatial spectrum of sediment density fluctuations. Perturbation ...

    • Temporal modeling of high frequency (30-100 kHz) acoustic seafloor backscatter: shallow water results 

      Sternlicht, D. D.; De Moustier, Christian (NATO. SACLANTCEN, 1997)
      A temporal model of high frequency seafloor acoustic backscatter is presented and compared to recorded echoes from terrigenous sediments. Using acoustic properties correlated with mean grain size, the echo shapes and ...

    • Terrain mapping with forward looking sonar on unmanned underwater vehicles 

      Medeiros, Michael R.; Carpenter, Robert N. (NATO. SACLANTCEN, 1997)
      In the future, successful reconnaissance operations conducted in shallow water with Autonomous Underwater Vehicles will rely heavily on a high performance, high resolution, forward look sonar coupled with terrain mapping ...

    • Texture analysis of sidescan sonar imagery using statistical scattering models 

      Griffiths, Hugh; Dunlop, Jonathan; Voles, Roger (NATO. SACLANTCEN, 1997)
      It is shown that the generalised K-distribution provides a good fir to the amplrtude statisttcs of sonar imagery from several different types of seabed sediment. A number of possible explanations for the Ricean nature of ...