HR: 1330h
AN: T12B-0459 [PDF]
TI: 3.5kHz Profiling with Vertically Separated Source and Receiver
AU: * Bolmer, S T
EM: tbolmer@whoi.edu
AF: Department Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02574-1542 United States
AU: Hoskins, H
EM: hhoskins@whoi.edu
AF: Department Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02574-1542 United States
AU: Stephen, R A
EM: rstephen@whoi.edu
AF: Department Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02574-1542 United States
AU: Leg 200 Shipboard Scientific Party, .
EM: odp@odpemail.tamu.edu
AF: Ocean Drilling Program, Texas A&M University, College Station, TX 77845-9547 United States
AB:
The spatial resolution of hull mounted 3.5kHz echo sounding systems is often limited in deep water by the large footptint
(Fresnel zone) of the insonifying energy on the seafloor. On ODP Leg 200 at Site 1224, we tested a system that could be used
from the drillship while on station to improve resolution. In 4970 m water depth, a 3.5 kHz pinger was mounted on the video
camera frame and lowered down the drill string to a few meters above the seafloor. The ship's 3.5 kHz receiver recorded the
returns. Having the source and receiver at differing distances above the seafloor provides two advantages: 1) the area
returning reflections is greatly reduced, 2) the amplitudes of the sub-seafloor reflections are less affected by the
spreading effect. Reflections were observed to 38 ms beneath the seafloor on lowerings at three closely spaced holes. The
heave of the ship and camera frame shifted the travel times of the reflection sequences. A level-discriminator and
correlation MatLab routine was used to align the traces and to stack them to enhance signal. The reflections showed good
correlation with the limited geotechnical data obtained from the sediment cores. Although tested from the drill ship this
system could be used to provide a low cost, shallow penetration profiling system from ROV's and AUV's. This work was
supported by a grant from JOI-USSAC.
UR: http://www-odp.tamu.edu/publications
DE: 3025 Marine seismics (0935)
DE: 3094 Instruments and techniques
DE: 3099 General or miscellaneous
DE: 7220 Oceanic crust
DE: 9355 Pacific Ocean
SC: Tectonophysics [T]
MN: 2003 Fall Meeting