Wednesday, September 1, 2010

OBS Recovery!

Hello! Remember those seismometers we sent to the bottom of the ocean a little over a month ago? Well we are currently in the process of resurrecting them from the abyss and hopefully they are pregnant with scientifically illuminating data seismic data.

The OBS recovery process is fairly straightforward, consisting of a few steps. First we must navigate to the location above the instrument. Once we are on site, the OBS guys begin their dialog with the instrument via acoustics and send the instrument the release command. The OBS is anchored to the seafloor by a steel plate that is attached by a metal cable. When the release command is sent, an electric current is sent through the metal cable and it dissolves. The process that causes the cable to dissolve is known as electrolysis, which is a chemical reaction that occurs with the assistance of electrical current. After the OBS is liberated from its seafloor anchor, it begins its 70 meter per minute accent to the surface. Some of the OBSs are being recovered from depths just over 3,000 meters. From such depths, it takes the OBS around 45 minutes to float to the surface!

Once on the surface, we must gain a visual report of it, then navigate to its location. It is sometimes quite difficult to maneuver a ship as large as the R/V Langseth around in order to collect a relatively small OBS. Once we are next to the OBS, we hook it and haul it on board using the A-frame winch. The salt water is the washed off of the OBS and it is secured for transit to the next OBS site. We have been averaging about 3 hours per OBS recovery and it will take us roughly 2.5 days to recover them all.

The OBSs are then taken back to Woods Hole Oceanographic Institute in Massachusetts, where the data is extracted from the instrument, QCd, and processed.

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