90-day Monitoring Report - National Marine Fisheries Service - NOAA

The source array utilized a mixture of Bolt 1500LL and Bolt 1900LLX airguns ranging in volume
from the smallest airgun of 40 in³ to 360 in³. The array contained ten airguns, with the first and
last spaced 16 meters apart. All ten airguns on the array were firing during survey acquisition.
The total volume of the array was 1830 in³ and a pressure of 1950 psi. Each discharge of the
source consisted of a single brief pulse of sound (duration of approximately 0.1 second) with the
greatest energy output occurring in the two to 188 hertz frequency range.
The shot interval for the MCS survey was 15 seconds. The sound signal receiving system
during the acquisition of the MCS transect lines consisted of a single six kilometer long
hydrophone streamer, which received the returning acoustic signals and transferred the data to
the processing system located onboard the vessel. Due to the length and placement of the
cables, the maneuverability of the vessel was limited to turns of five degrees per minute while
the gear was being towed.
Sonobuoys were also deployed up to four times per day (occasionally more if a sonobuoy failed)
during seismic operations on MCS line acquisition. A total of 108 sonobuoys were launched,
each consisting of a hydrophone, electronics, and a radio transmitter that measured the seismic
signal then transmitted the data back to the ship, for up to eight hours before sinking to the
ocean bottom.
In addition to the operations of the airgun array, a Kongsberg EM 122 multibeam echosounder
(MBES), a Knudsen Chirp 3260 sub-bottom profiler (SBP), and a hull-mounted acoustic Doppler
current profiler (ADCP) was operated from the Langseth continuously throughout the cruise.
These sound sources are operated from the Langseth simultaneously with the airgun array.
UME04085
R.V Marcus G. Langseth
L-DEO/NMFS
05 January 2012
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