SWellEX-3 was an experimental study of shallow-water propagation and matched-field processing conducted 10 km off San Diego in July, 1994. Data were recorded on a 64-element, 118-m aperture vertical line array anchored in 200 m of water. A cw source emitting tonals from 53–197 Hz was towed over tracks where the water depth varied from 200–75 m. Examples of range-dependent matched-field processing of this multitone signal using the finite-element parabolic equation program for propagation modeling will be presented.

Detailed seafloor environmental modeling of a moderately complex shallow water area, coupled with multitone matched-field processing, produced reliable and unambiguous source detection and tracking. Frequency averaging of the matched-field output sufficiently reduced sidelobe ambiguities. The seabed geologic model is a gridded database containing water depth, sediment grain size, sediment thickness, and acoustic basement type. Grid cells are squares of side length equal to 2 arc s. Software, separate from the geologic model, computes a geoacoustic model for any desired grid square.

The SWellEX-1 (shallow-water evaluation cell) area is a complex shallow water environment of approximately 400 km2 immediately offshore of San Diego, California. In it, thinly sedimented terraces separate steep scarps. The terraces and scarps are old erosional surfaces with moderate relief. Sediment thickness ranges from zero to tens of meters over a basement of sandstone and mudstone. The IDRISI geographic information system was used to assemble and analyze geologic and geoacoustic data, and to provide that data to a database server that will support high-fidelity acoustic simulation codes. Data for the initial effort consisted of SeaBeam and National Ocean Service depth soundings, published geological maps, published sediment thickness charts combined with the results of a shallow seismic reflection survey, and published sediment charts. Data provided to the acoustic codes at a grid spacing of 2 arcseconds are depth; sediment thickness; sediment compressional and shear properties and density (varying with depth in the sediment); and basement properties.

Abstract : A three-dimensional database containing water depth, sediment thickness, surface and basement rock type, and surface sediment mean grain size is provided, which, when combined with generic sediment and rock geoacoustic properties (also provided) produces a geoacoustic description of the Catalina Basin. Mean grain size is used as an index to acoustic properties. The database is gridded at 15 seconds of latitude and longitude. Geoacoustic model, Catalina Basin

Measurements of four of the five elastic stiffnesses of marine calcareous rocks and estimates of the fifth, c13, allow more detailed discussion of elastic wave propagation in these rocks than previously possible. The constant c13, which is seldom measured and was not measured in the rocks of this study, was derived by equating the Gassmann and Hashin‐Shtrikman estimates of the bulk moduli of chalk and limestone and then solving for the single unknown c13. For chalk, the measured constants, in N/m2×1010, are c11 = 1.01, c33 = 0.94, c44 = 0.18, and c66 = 0.21. For limestone, the measured constants, also in N/m2×1010, are c11 = 2.41, c33 = 2.09, c44 = 0.47, and c66 = 0.60. Three physically possible values of c13 were computed for chalk (0.48, 0.52, and 0.63 N/m2 ×1010) and for limestone (0.73, 1.05, and 1.24N /m2×1010). Heretofore, the only statements which could be made about c13 in these rocks are |c13| < 0.87×1010 N/m2 (chalk), and |c13| < 1.94×1010 N/m2 (limestone). The calculations require the assumption that anisotropy in these rocks is caused by mineral alignment and the simplification of monomineralogy (calcite). On the basis of these measurements and estimates, the effect of elastic anisotropy on seismic reflection determinations of vertical compressional wave speed in calcareous rocks below the earth's surface is small ( ±6%), whereas similar determinations of vertically polarized shear wave speeds may be unreliable. Relationships are provided to convert seismic refraction measurements of horizontal compressional wave velocity to vertical velocity. These relationships are independent of the estimated values of c13.

Eight variable-angle seismic reflection stations in the Arabian Fan, Northwestern Indian Ocean, provided 40 determinations of sound velocity in sediment and sedimentary rock. Sound velocity in the homogeneous, largely terrigenous fan increases smoothly with depth. Regression analysis yielded the velocity-time relationship V (km/s) = 1.510 + 1.863t, where V is instantaneous velocity and t is one-way travel time below the sea floor to I s. The velocity-depth function is V (km/s) = 1.510 + 1.200h - 0.253h: + 0.034h 3, where h is subbottom depth in km.