Dear Friends,
My apologies for a belated November update. In the first two weeks of November, our NFSI team overseen by 2 senior engineers from Guralp carried out our first deployment of 12 instruments offshore Nova Scotia, using R/V Strait Explorer. The operation started with 2 shallow water test drops on the Scotian shelf. Despite an instrument reset when it banged the side of the boat, and a breakdown of the ship’s bow thrusters when recovering the instrument, these tests allowed us to work out details of our deployment strategy in calm waters.
As we prepared to sail for deep water a significant storm was developing, to be followed by a second major storm with 9-10 m waves forecast. There was a real concern about whether it was safe to head out, and the entire deployment was in question. After studying weather maps for a day, we finally decided to take a chance on a ~30 hr lull between the fronts, planning to deploy the instruments as fast as we could on a reduced 20 km grid (rather than 40 km spacing as originally planned) and position them when we return next year.
We transited to the survey site on the tail of the first storm, with equipment flying around and many seasick, but as we arrived on site the seas started to calm. The deployment operations went quickly, continuing nonstop for about 24 hrs, with our tech team performing very efficiently. We communicated with the instruments acoustically for the first few 100 m of their descent to make sure everything was working. One of the instruments reset during this communication. We did not have time to recover and redeploy it, but other than loss of clock synchronization it should record normally.
Having a few hours of calm weather remaining when we had finished deployments, we tried to communicate with some of the instruments on the seafloor. This proved very difficult. Tests suggest this was due to mounting the acoustic modem, or “dunker”, on the end of a pole which was transferring vibrations from the ship to the dunker, masking the signal. We are looking into alternative configurations for recovery next year.
While our team was deploying OBS offshore, Miao Zhang and his students deployed a complementary array of 72 land seismometers along the east coast of Nova Scotia. 2.5 weeks after the cruise, when we were back in Halifax, we received a message from the GPS beacon that one of the instruments had surfaced unexpectedly. A few days later, a second instrument surfaced. We are tracking the instruments on GPS. It is unclear what triggered the anchor releases. The most plausible explanation at this point seems to be a small current leakage between pins in the main connector which sends current to the burnwire but also supplies power to the hydrophone. This, along with causes for the 2 instrument resets observed, is currently being tested by Guralp.
This deployment brought to light some problems with the instruments which could not have been discovered in the lab. However, our quick turnaround to deploy them allowed us to discover and hopefully correct these issues very early in the batch manufacturing process.
Positive news on other fronts has been that the Canadian Navy is showing interest in deploying our instruments in the Arctic with the new Harry DeWolf-class offshore patrol vessels starting as early as next summer.
Best,
Mladen and Graeme