High Speed Transmission of Log Data

Contributed by the Borehole Research Group, Lamont-Doherty Earth Observatory (LDEO-BRG).

Beginning with Leg 166, LDEO-BRG has been routinely utilizing high-speed satellite equipment to transmit log data from the JOIDES Resolution to shore. Transmitting log data for rapid processing enhances the accuracy of shipboard logs data analysis and reporting and increases data quality control. Data are corrected for depth, borehole conditions, and environmental effects on shore, then returned to the ship within days of logging. This "near-time" response has been very well received by both the shipboard scientists and operations personnel.

The deployment of VSAT (very small aperture terminal) satellite equipment, leased from Schlumberger on a trial basis, has realized transmission rates up to 180 Kbps. VSAT equipment consists of a stabilized mount and antennae currently located on the helipad. Electronic equipment is integrated into the Maxis 500 data acquisition system making installation and operation extremely simple. Two antennae dishes and radios are available as the ship moves between various satellite coverage regions. A 1.2 meter satellite dish is utilized when in the Ku-Band footprint, typically located within 100 miles of the continental United States. When out of the Ku-Band footprint, a larger 2.4 meter dish and more powerful radio are installed to capture the less focused energy of the C-Band thus extending the effective coverage area of the system. Presently, the VSAT system coverage includes the waters adjacent to North America and the majority of the Atlantic including Africa. Satellite coverage, however, is not at present available in all oceans.

To extend beyond the operational limits of the VSAT system and to more fully integrate with ODP/TAMU operations, LDEO-BRG began investigation of other high-speed data transmission alternatives. During Leg 170, an Inmarsat B terminal was made available to ODP by the SeaNet program for testing. The unit had previously been used aboard the R/V Thompson. Inmarsat B satellite coverage is global between 70 degrees north and 70 degrees south latitude. The system is an ABB Nera Saturn Bm with a SeaNet Communications Node for high-speed (64 Kbps) data transmission. The lower transmission rates with this system, however, will make processing of images on shore prohibitively expensive.

Initial tests of log-data transmission from the JOIDES Resolution have been very successful. A joint satellite communication arrangement among LDEO, TAMU, and Sedco is the ultimate goal of the present tests. Both Sedco and TAMU personnel are examining these systems so that the most suitable system for ODP/TAMU as a whole can be chosen. It is anticipated that a permanent system will be in place in mid-FY 97.