Browsing Reprints by Issue Date

Now showing items 261-280 of 548

    • Multistatic bottom reverberation in shallow water 

      Schmidt, Henrik; Lee, Jaiyong; Fan, Huaiyu; LePage, Kevin D. (NATO. SACLANTCEN, 1997)
      A wavenumber integration approach to modeling of the full multistatic reverberant field produced by small-scale bottom roughness in stratified shallow water waveguides has been developed. A perturbation approach to rough ...

    • Sound absorption by suspended particulate matter 

      Brown, N. R.; Leighton, Timothy Grant; Richards, S. D.; Heathershaw, A. D. (NATO. SACLANTCEN, 1997)
      A series of experiments has been performed to study the viscous absorption of sound by particulate suspensions typical of those found in coastal waters. The effect due to the particles in the frequency range of 50 - 150 ...

    • Relating in situ shear wave velocity to void ratio and grain size for unconsolidated marine sediments 

      Huws, Dei; Davis, Angela; Pyrah, James (NATO. SACLANTCEN, 1997)
      Recent advances in field hardware have meant that it has become possible to measurein situ shear wave velocity in the upper few decimetres of sea floor sediment in a routine manner. It is known that shear wave velocity can ...

    • Physics of bottom scattering and some applications 

      Gensane, Marc (NATO. SACLANTCEN, 1997)
      The main bottom scattering theories are described in their bistatic formulation: composite-roughness, and volume scattering. Several applications are proposed. One of the main concerns is to check the mono- and bisfafic ...

    • Acoustic signal dispersion and distortion by shallow undersea transmission channels 

      Rice, Joseph A. (NATO. SACLANTCEN, 1997)
      The undersea littoral is an adverse medium for acoustic signal transmission to horizontal ranges of many water depths. Reflections and scattering in the bounded, nonhomogeneous channel disperse the arrivaj of received ...

    • Advances in cots side scan sonar for MCM applications 

      Kozak, Garry (NATO. SACLANTCEN, 1997)
      The Persian Gulf War has elevated the awareness to the problems of shallow water mine detection. Today's high technology shallow water anti-invasion mines, such as the Italian made "MANTA" and the Swedish manufactured ...

    • Bayesian inference and sidescan restoration 

      Calder, B. R.; Linnett, L. M. (NATO. SACLANTCEN, 1997)
      We consider a Bayesian approach to the problem of inferring parameters of the SONAR environment given only the gathered sidescan image. A simplified model of the process is developed along with suitable distributions on ...

    • Source and receiver responses in boreholes 

      Hovem, Jens M.; Lotsberg, Oddvar (NATO. SACLANTCEN, 1997)
      This report considers the acoustic interaction between the acoustic freld rn a borehole and the elastic field in the surrounding formation. The problem with acoustic-seismic radration of energy from a source in a fluid ...

    • Shallow-water coherence of broadband signals 

      Badiey, Mohsen; Simmen, J.; Tang, X. (NATO. SACLANTCEN, 1997)
      The frequency-dependent spatial and temporal variabilities of sound propagation in coastal regions is investigated by ezperiment and numerical simulations. Experimental observations show that temporal coherence of 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 ...

    • Critical angle and seabed scattering issues for active-sonar performance predictions in shallow water 

      Del Balzo, Donald R.; Leclere, James H.; Collins, Mona J. (NATO. SACLANTCEN, 1997)
      Active sonar performance predictions (0.75 to 3 kHz) are examined in summer shallow-water environments to quantify the impact of variable seabed and watermass properties on detection. Scattering is computed with an ...

    • Bottom bistatic scattering: experimental results and model comparison for a carbonate sediment 

      Williams, Kevin L.; Jackson, Darrell R. (NATO. SACLANTCEN, 1997)
      Bistatic scattering measurements were carried out under the Coastal Benthic Boundary Layer (CBBL) program. The results presented here are for a carbonate sand-silt-clay, and the data were collected in Februar) 1995 near ...

    • Sedimentological acoustics: an attempt to reduce the gap between acoustical modeling and sedimentoloogical survey 

      Garlan, Thierry; Demoulin, Xavier (NATO. SACLANTCEN, 1997)
      A major task in shallow water acoustics is to provide pertinent geoacoustical data. The purpose of the work is to evaluate the state of the art in this field, connecting in situ sedimentological measurement and acoustical ...

    • A high frequency approach for seabed vegetation characterization 

      Bozzano, Roberto; Siccardi, Antonio (NATO. SACLANTCEN, 1997)
      This paper focuses on the characterization of seabed vegetation, an interesting problem in a lot of Mediterranean sea coastal sites since water quality and pollution degree can be efficaciously solved by investigating the ...

    • Acoustic characterization of submerged aquatic vegetation 

      McCarthy, Elena (NATO. SACLANTCEN, 1997)
      The acoustic characteristics of submerged aquatic vegetation (SAV) were investigated in order to enhance the performance of mine-hunting and weapon sonars in littoral reglons. The specres of seagrass initially studied was ...

    • The effect of water column stability on acoustic backscatter from the ocean bubble layer 

      Bekker, Kathy K.; Gilbert, Kenneth E.; Goodman, Ralph R. (NATO. SACLANTCEN, 1997)

    • Modeling range-dependent, high-frequency, shallow-water torpedo reverberation data 

      Keenan, Ruth Eta; Weinberg, Henry; Aidala, Frank E. (NATO. SACLANTCEN, 1997)
      The high-frequency, forward bottom losses predicted by a lossy Rayleigh and a Biot poroelastic sediment model are substantially different. These differences will accumulate and become measurable in multiple bottom bounce ...

    • Geoacoustic modeling of the seabed at higher frequencies 

      Stoll, Robert D.; Bautista, Edgar O. (NATO. SACLANTCEN, 1997)
      In propagation at higher frequencies, local fluid motion in "hidden coordinate" systems and local discontinuities due to gas bubbles and bioturbation have a perturbing effect on the wave field. To model these effects, a ...

    • Riverine environmental acoustics at an ocean estuary 

      Muir, Tom G.; Blue, J. E.; Anderson, A. L. (NATO. SACLANTCEN, 1997)
      The purpose of these studies was to investigate some of the more important geoacoustrc parameters that might govern the use of high frequency sonar in muddy rivers, where they flow into the sea. Both environmental and ...

    • Effect of waveform on synthetic aperture sonar performance 

      Guyonic, Stéphane (NATO. SACLANTCEN, 1997)
      This paper describes the main properties of the synthetic aperture sidescan sonar and highlights performances and limitations related to sonar features for mine counter measures. Attention is focused on the theoretical ...