Cruise Blog by Frances Cooke: Day 4
July 10th, 2021
Text and photo: Frances Cooke (PhD Candidate in the Gas Hydrates and Free Gas Reservoirs research group at CAGE, working within the SEAMSTRESS project).
While the night shift took some rest, we successfully recovered one OBS (no. 10) at the northern termination of Knipovich ridge (NKR). The original plan was to recover two OBS but the visibility was too poor. The breaking waves made the search for the OBS a difficult task!
Clock Drift
‘DIRC’ Clocks in the OBS are temperature sensitive. When the clocks are recovered they need to be synchronized right away before they warm. They are synchronized at the beginning (pre-deployment) and at the end (on recovery). It is known that during the experiment the clocks drift linearly. This clock error is applied automatically which addresses the linear drift problem. However, there is also non linear drift which is a much more time consuming fix (requiring several weeks of processing). Vera tells me that the new manufactured (AWI) seismometers were fitted with clocks that have worse drift than the old seismometer clocks. They are less power consuming but the processing as a result is more time consuming!
The seismic deployment began at midnight, and we were ready to start our first 2D seismic line by 01:30 AM. During the night shift we will complete at least 2 survey lines that will take approximately 3 hours each to shoot (line distances: ~25 km). The sea feels a little rough (2m swell), but by tomorrow evening the wind will drop.
Bathymetry map displaying NKR survey area with seismic lines and OBS pick up locations (orange), the red cross marks the retrieved OBS no. 10 (recovered late in the evening on day 3)
We completed four seismic lines, finishing the last line just after 18:00. We had to stop work and recover the seismic instrumentation after an incident onboard required a helicopter rescue. We had planned to start OBS recovery at midnight during the calm weather, but now we will head to Longyearbyen and wait for a replacement crewmember to join us.
A very impressive and quick helicopter rescue operation
Read more about the SEAMSTRESS project here.
