Seismic profiling: it all starts with a Pulse

The Ewing could tow up to twenty pneumatic sound sources from its twin 40-foot booms. Up to six pneumatic sound sources could be towed without the booms. The "standard" array used for deep penetration seismic profiling consisted of 20 Bolt 1500-C acoustic generators, varying in volume from 80 to 850 cu. in., with a total volume of 8580 cu. in. (140 liters). Originally, towing depth depended on ship speed and the length of the tow leaders. Typical tow depths ranged between 6 and 9 meters. From1998 and onwards, the sound sources were towed beneath floats, which held the tow depths more consistently, at 6  - 8 meters.
At the typical tow depth of 7.5 meters, the peak-to-peak far field output of the array is 134 bar-meters, with a peak-to-bubble ratio of 8.6:1. Towing deeper enhances low frequencies, at the expense of peak-to-bubble ratio (7.6:1 at 9 meters), while shallow towing enhances higher frequencies and increases peak-to-bubble ratio (10:6 at 6 meters).
For imaging of sedimentary and shallow crustal structure, use of the full 20 sound source array was not beneficial. Reverberations from previous shots may raise background noise to disavantageous levels. For these targets, subsets of the larger array, totalling six or ten sound sources were preferred.

Click here for a description of the proposed Langseth Source array