Wednesday, July 17, 2013

Dana Fields's Internship, Summer 2013 - Part 3

Well I’m back at a desk wrestling with MATLAB. Aided and abetted by my mentor, Dr. Nico Wienders, I’m starting to make progress.

In my first blog entry, I mentioned that I am working with data collected by the CTD (conductivity, depth, and temperature) divers that were deployed at the head of the DeSoto Canyon. Deep-C researchers have several mooring stations in the DeSoto Canyon area, but these particular instruments were located at mooring sites 1 and 3 (see Figure 1 for the mooring locations). These instruments were attached to mooring cables that were anchored to the ocean floor with three locomotive (train) wheels. The instruments were placed 5 to 10 meters apart along the cable. The mooring cable was held upright with flotation spheres, and the top of the cable was 15 meters below the surface to, hopefully, avoid fouling by boats. A marker float was attached to the top of the mooring with a 20-meter string. (Figure 2 is a diagram of the mooring cable deployed at Mooring 1.) As it turns out, the cable at mooring 3 was broken, probably by a trawling net, and all but the two instruments were lost.
Figure 1: Mooring sites 1 and 3 in the DeSoto Canyon area.

Figure 2: A diagram of the mooring cable deployed at Mooring 1.
The CTD Divers are nifty little instruments made by Schlumberger. They are traditionally used to monitor groundwater and haven’t been previously deployed in the ocean. These instruments were deployed May 2012 and recovered May 2013. Though the original intent was to collect data every 3 seconds for that year, in the final deployment they were configured to record depth, temperature and salinity every 15 minutes. (Trust me, that still ends up being a lot of data points!) Figure 3 shows a new CTD Diver and one of the recovered instruments. Notice that the deployed CTD Diver was covered with a shield to, again hopefully, prevent fouling by sea organisms (primarily barnacles). Unfortunately, the shield was only partially successful. Most of the instruments ended up with barnacles inside them, which interfered with the conductivity measurements, though depth and temperature seem to be unaffected.

Figure 3: A new CTD Diver (left) and one of the recovered instruments (right).
So anyway, 12 CTD Divers were deployed and 7 survived. One of the sensors (the top one) on Mooring 1failed so that no data could be retrieved. All but two of the sensors associated with Mooring 3 were lost completely. I’ve been using MATLAB and Excel to plot the collected data (Figure 4). I’ve already been able to identify how the tides affected the temperature and depth data. There are some interesting “blips” that we may be able to associate with storm activity… but I haven’t made it that far yet. I still have to learn how to apply filters to the data so we can screen out the responses we know about and identify other phenomena (currents, etc). By next week, I should know even more!
Figure 4: Using MATLAB and Excel to plot the collected data.
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Dana Fields (Florida State University)

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