Tuesday, June 3, 2014

Research Cruise UPDATE: Focus on collecting multi-core samples while MILET is out of commission

The navigation pinger is attached to the coring winch wire
above the core
With the MILET temporally out of commission, the priority of the sampling has shifted to collection of multi-core samples, usually three per site, with a CTD profile at each site and piston cores plus water sampling at selected sites. The bongo net is also out of commission, so this activity has dropped from our operations until a replacement is obtained. To make things go faster, and ensure that everyone gets some sleep every day, we have divided the science party into two teams — Team Garnet and Team Gold naturally. Starting at 18:00L on 2 June, Team Garnet completed a piston core, CTD with water samples, and three multicore drops at the XC-1 site. Team Gold took over at 05:00 on 3 June and collected a CTD profile, three multicore drops and a piston core at the XC-2 site. Weatherbird-2 is underway to the S36 site to continue the sequence. 

The pole mounted transponder
(out of the water for transit)
and the GPS unit at the top of the
frame track the pinger an the pole position
We are still planning to put into Panama City on the evening of 5 June to repair the MILET cable. We’ll return to work, departing about 17:00L the next day. Weather forecasts are favorable, so we anticipate completing our sampling and returning to St. Petersburg on morning of 13 June. From left: The navigation pinger is attached to the coring winch wire above the core; the pole mounted transponder (out of the water for transit) and the GPS unit at the top of the frame track the pinger an the pole position; the navigation screen displays the location of the core on the bottom. 

All multi-core and piston core drops are navigated using an ultra short baseline system. A transponder is attached to the cable about 20m above the corer. A surface transponder mounted on a pole on the side of Weatherbird-2 interrogates the pinger to get the range and bearing between the pinger and the ship. We have a dedicated survey-grade GPS unit mounted just above the transponder pole. Some advanced geometry then enables our IPS software package to get a position of the pinger as it approaches the bottom. Having these navigation data for the cores improves accuracy of comparison to subbottom features and among the three or four multi-core. 

The navigation screen displays the location of the core on the bottom
 Posted by:

Ian MacDonald
Florida State University

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