We used 4 SODERA-SSI GI-GUN with different volume chambers, ranging
from 150 to 250 in
each. The deep penetration survey was accomplished with
a synchronized array of two guns in Harmonic Mode Configuration 105+105 in
(6.9 L) and 150+105 in (8.2 L), while the high resolution survey used a single gun in True
GI configuration 45+105 in (2.46 L). The guns were equipped with REF-TEK hydrophones
and Accelerometers for the Time Break detection. The pressure was set to 138 bar for the deep
penetration survey, whilst it ranged from 130 to 200 bars for the high
resolution one. Some deep-penetration line was run with the two gun array
powered at 200 bar, in synchronized Harmonic Mode, for on-shore station recording. One of this lines,
crossing C.S.Vicente, used 500 in (8.2 L), while the other were set to 420
in.
Shot distance ranged from 25, 37.5, 50 to 100 m, and was controlled
by IGM's NAVMAP Navigation System and GI-GUN Synchronizer MASINI1995, with the former
providing the shot timing information to the latter, which in turn provided time
break and syncronization signals to the guns. In particular, the array
synchronization was performed by measuring the response of any gun to Time
Break after (a) cross-correlating the signals
from gun hydrophones or (b) timing the Time Break Accelerometric Detector
signals at the first zero-crossing, and displacing the appropriate delay or anticipation around a fixed
delay of 10 msec at Time Break. The injection delay for each gun was set in
order to have the best Peak to Bubble ratio, as shown on a monitor for each shot.
The source was powered alternatively by IGM's Bauer Mod. I28 (2500 L/min @ 250 Bar, regulated 0 to 210 Bar) and UGBO's Hamworthy Mod.TH-190-W70 (5000 L/min @ 140 Bar) through a 80 L bottle reservoir installed on IGM's Bauer I28. The Hamworthy was put into operation with an excess pressure discharge circuit, to avoid machine stops at maximum delivery.