ASA 124th Meeting New Orleans 1992 October

1aUW6. Small scale lateral variability of geoacoustic properties of the upper 40 m of the seafloor.

Dennis A. Lindwall

Joseph F. Gettrust

Naval Res. Lab. Detachment, Code 362, Stennis Space Center, MS 39529-5004

The spectral response versus grazing angle of the seafloor sediment for several kilometers of deep towed, multichannel seismic reflection data from Atlantic seafloor near the Blake outer ridge shows variations of as much as 15 to 20 dB in bottom loss over distances of less than 50 m. A video of this spectrum versus offset (SVO) data, which explicitly shows the lateral variations as the DTAGS instrument is towed along just above the seafloor, is presented. A few regions of anomalously high shear wave velocities also are identified in these observations. These data demonstrate that a seemingly smooth seafloor can be a rough, frequency-dependent scattering surface. [This work is supported by the Office of Naval Technology.]