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Laboratory Methods


Underway Geophysics

Lab Documentation

The Underway Geophysics Laboratory on the JOIDES Resolution aquires navigation, seismic reflection, bathymetric (3.5 and 12 KHz), and magnetic field data. In addition to collecting scientifically useful data, a primary function of these data are to ensure drilling safety by reconfirming site positions and disinguishing seafloor and sub-seafloor characteristics. Navigation and seismic data are used to ensure the ship is drilling in the position that has been reviewed and approved by the Pollution Prevention and Safety Panel (PPSP) and by the internal ODP safety panel.

GPS can be used as emergency backup in case of a dynamic positioning system (DPS) failure (e.g., a seafloor beacon failure). GPS data will allow the ship to maintain position over the site while the drill pipe is pulled out of the hole. In addition, high-resolution echo-sounder data (3.5 and 12 KHz) can be used to determine the seafloor and subseafloor geotechnical characteristics such as slope and shallow subbottom characteristics. The principle navigation equipment on the JOIDES Resolution is an Ashtech GG24 Sensor System (GPS+ GLONASS).

Data Collection

ODP collects navigation data at all times while under way, even when no geophysical data are collected. Navigation data are automatically collected from various sources (heading, speed, wind, Transit and GPS satellites) and are stored on magnetic tape for reduction into a smooth cruise track. Geophysical data (bathymetry, seismics, magnetics) are collected whenever possible while under way and systematically during site surveys. When necessary, ODP is responsible for obtaining permission to collect underway geophysical data from the appropriate coastal states. The decision to collect this data is made during the Co-Chief Scientists pre-cruise meeting, and is based on the need to collect data in under-explored or key areas. During the cruise, collection of geophysical data can be vetoed by the captain for safety considerations.

Equipment

Seismic Guns

  • 3 /80 cubic inch SSI water guns.
  • 2 /200 cubic inch Hamco water guns.
  • 1 /400 cubic inch SSI water gun.
  • 1 /1500 Bolt Airgun capable of 120 to 1000 cubic inch

Streamers

  • 2 Teledyne single channel, 60 phone, oil filled.

Bathymetrics

  • 3.5 KHz - EDO tranceiver with single-element 10 kw transducer
  • 12 KHz - PTR 105B transceiver with EDO 323B transducer
  • 2 CESP-III Correlators (~20-db signa-to-noise improvement)

Navigation

  • Ashtech GG24 Sensor (GPS+Glonass)
  • 2 /Omnistar dGPS capable receivers.

Software

  • Winfrog Realtime Navigation System
  • Unix Seismic Data Aquisition System

Imaging

  • 4 EPC Model 9802 Thermal Graphic Recorders
  • HP DesignJet 650C Large Format Color Plotter

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