WHOI Technical Reports

Permanent URI for this collection

https://hdl.handle.net/1912/554

The Woods Hole Oceanographic Institution publishes technical reports describing projects carried out by WHOI researchers. New reports are added as they become available.

Pre-1978 reports are scanned and added by request; contact the WHOAS project manager whoas@whoi.edu to have a Technical Report added.

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Browsing WHOI Technical Reports by Subject "Acoustic models"
  • Technical Report
    Calculation of 3-dimensional synthetic seismograms on the connection machine
    (Woods Hole Oceanographic Institution, 1989-10) Allen, Julie M. ; Burns, D. R.
    A three dimensional, second order finite difference method was used to create synthetic seismograms for elastic wave propagation in heterogeneous media. These synthetic seismograms are used to model rough seafloor, the shallow crust, or complex structural and stratigraphic settings with strong lateral heterogeneities. The finite difference method is preferred because it allows models of any complexity to be generated and includes all multiple scattering, wave conversion and diffraction effects. The method uses a fully staggered grid as developed by Virieux (1986). Wavefront snapshots and time series output allow the scattering and focussing of different wave modes with direction to be visualized. The extensive calculations required for realistic size models stretches the resources of serial computers like the VAX 8800. On the Connection Machine, a massively parallel computer, the finite difference grid can be directly mapped onto the virtual processors, reducing the nested time and space loops in the serial code to a single time loop. As a result, the computation time is reduced dramatically.
  • Technical Report
    The contribution of normal modes in the bottom to the acoustic field in the ocean
    (Woods Hole Oceanographic Institution, 1981-04) Macpherson, Mark K. ; Frisk, George V.
    The effects of normal modes in the bottom on the acoustic field in the ocean are examined. The ocean bottom model consists of a slow isovelocity layer overlying an isovelocity half-space to simulate the characteristic sound velocity drop at the water-bottom interface. Attention is focused on the perfectly trapped modes which are excited in the layer by inhomogeneous waves emitted by a point source in the water column. The relative normal mode contribution to the total acoustic field in the water is calculated analytically for a near-bottom source/receiver geometry and evaluated for representative ocean bottom examples. It is shown that, for combined source/receiver heights less than a wavelength, the field is dominated by the leaky mode contribution at short ranges ( $ 2 km) and the trapped mode contribution at long ranges ( ~ 2 km). For fixed bottom parameters, the trapped mode contribution increases exponentially with decreasing combined source/receiver height. It is also shown that, for a fixed layer wavenumber-thickness product and fixed layer sound speed, the leaky mode fields at different frequencies are approximately range-scaled versions of the same field.
  • Technical Report
    FINDIF : a software package to create synthetic seismograms by finite differences
    (Woods Hole Oceanographic Institution, 1983-11) Hunt, Mary M. ; Gove, Lee ; Stephen, Ralph A.
    In order to study seismic wave propagation through laterally varying sea floor structures, a software package has been created to generate synthetic seismograms by finite differences. The elastic wave equation can be solved in two dimensions either for point sources in cylindrical coordinates or for line sources in rectangular coordinates. Vertical and radial variations of the elastic parameters are allowed. The package includes four programs. Input to the system consists of a short file containing parameter values to describe the model. The first program is used to initialize the system for the particular model being used. The source arrays and velocity matrices are each computed by a separate program. The final program, which actually carries out the finite difference calculations, includes six subroutines to implement different options based on alternative finite difference formulations. Two different kinds of output files are created by this program: one or more snap-shot files, and one time series file, which will usually include more than one series.