High resolution multichannel seismic were performed using an array of two synchronized SERCEL (formerly SODERA-SSI) GI-GUN (Fig.13), (in the 105+105 c.i. Harmonic configuration) pneumatic sources, powered by a 2500 L/Min, electrically driven, Mod. I28 air compressor by BAUER. The pressure to the gun was set to 140 Bar (2500 psi), actually ranging between 125 and 145 Bars. The seismic data were collected by a MOD.29500 TELEDYNE 48 channel streamer (Fig.15), digitized and recorded on DDS-1 and DDS-2 DAT tapes by a OYO-GEOMETRICS's STRATAVISOR seismograph in the SEG-D 8048 Revision.0 format, with sampling rate of 1 msec and record lenghts of 12 secs. The group interval was 12.5m for a total active length of 600 m. The 150 m tow leader and two 50 m stretch sections made up the streamer to a total length of 850 m. The seismic source was fired by IGM's gun-control equipment [Masini and Ligi (1995)] (14), that introduced a fixed delay of 10 msec from the time break, where the injector delay floated around 44.5 msec. Shot distances were of 50 m, thus achieving coverages of 600%. The time break was provided by the seismic module in the NAVPRO software, with the DISTANCE FROM PREVIOUS SHOT setting, in order to maximize the survey flexibility allowing the SHOT NOW capability when enroute. The depth of the source ranged between 5 and 6 m. The streamer was kept at 10-12 m depth with SYNTRON RCL-2 cable-levelers, using a Teledyne Mod. 28951 depth control system.
The data were processed onboard using the DISCO/FOCUS packages by PARADIGM, up to the time-migration of some sections, using a standard processing sequence.
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