Leg 187 Site 1152 was located based on 1997-vintage single-channel seismic data, plus a short 3.5-kHz PDR and SCS survey conducted on approach to the site. Onboard instrumentation used included a precision echo sounder, gyrocompass, seismic system, and GPS receivers.
Both 3.5- and 12-kHz PDRs were used to acquire bathymetric data as well as high-resolution reflection records of the uppermost sediment layers.
Site selection for the first drill site of Leg 187 (Site 1152) was based on a SCS survey conducted during R/V Melville cruise Sojourner 5 in 1997. A ~1.4-hr SCS survey was conducted on approach to Site 1152 (JR SCS line S1; Fig. F10) to ensure the correct site location by comparing the GPS-navigated SCS data with the 1997 SCS image. The ship's speed averaged 5.7 kt during the SCS survey. The water gun was triggered at a shot interval of 12 s, equivalent to ~35 m at 5.7 kt. Data acquisition and processing parameters were described in "Underway Geophysics" in the "Explanatory Notes" chapter. There are several course changes in line S1 as the ship maneuvered to approach the site on a north-south line; the ship's heading was 130°, 160°, and 180° from ~02:20, 02:54, and 03:10, respectively. The final position of Site 1152 was shifted ~2.7 km south of the prospectus site AAD-36a to an apparently thicker sediment pond. We marked this position near seismic shot number 301 of line S1. The depth at the site is 5066.4 m (see Fig. F11), with sediment cover from 6.8 to 6.95 s two-way traveltime, estimated to be ~150 m. The 3.5-kHz analog data were used to confirm this selection.