My Geology professor, Dr. Brooks, once said to our class, “every time that you put equipment overboard, you have to accept that there is a chance that it will not be returned to you.” Now, I liked this phrase because it carries with it, the idea that marine field work, in particular, puts a lot of ‘wear and tear’ on the equipment we use, which is a testimony to the hostile environment that we work in. The basic point is, however, that a good portion of every research cruise is spent calibrating the equipment for a specific task at hand, maintaining the equipment to keep it from getting broken, and fixing equipment if it does happen to fail.
Fortunately, so far we have not lost any equipment on this cruise, ::knocks on wood::, but there has been some necessary maintenance, which has given me the opportunity to better acquainted with some of the equipment on board. Steffen is our resident Mr. Fix-It, so I tend to stick fairly close to his side when I know that things need to be fixed.
The biggest project, so far, that the team has tackled had to do with the ‘streamer’. So, the streamer is a line of hydrophones inside of a thick rubber tube that is filled with oil (not sure what type, somewhere between crude and canola), which performs two purposes: First, it allows for easier propagation of sound to the hydrophones (air is a terrible medium). Second, and more importantly, it makes the stream closer to neutrally buoyant so that it neither rides on the surface, nor scrapes the bottom. If the streamer is on the surface then our data becomes muddied with a lot of low frequency noise, but if it hangs too low, then there is a greater chance that it will catch on some debris floating within the water column.
So, our task was to make the streamer as close to neutrally buoyant as possible. To do this, however, we needed to know how deep the streamer was sitting in the water column, which was accomplished through the use of three transducers. A transducer, for those that do not know, is a device that measures and records the pressure that it is experiencing at a particular moment (e.g. once a minute) and then stores those values within itself. The pressure can then, with some compensations and correction, can be correlated to find the depth in the water that the transducer was while it was recording. This is really useful, because no wires are necessary, you just attach the transducer to the equipment where ever you want to know the depth and then take off the data at the end of the day.
We took a day of data, which showed that the streamer had an average of about 6 – 8 meters, which was far too deep. The optimal level would be around 1 – 2 meters. So, the next day we added a LOT of flotation along the streamer. Of course, this resulted in the streamer floating on the surface, which made for less than desirable data. The next day was spent taking the streamer in and out of the water to remove floats to the point where we saw the streamer LESS than before, but the data at the end of the day showed that it was still running shallow. Finally, on the third day, we removed a smidgen more floatation and the data showed that streamer was floating around 2 – 3 meters consistently, except whenever eddies suck a part of the streamer down to 10 meters (this another major worry of ours).
Similar customization had to occur for the electronic equipment used in the lab, the CHIRP, and the airgun, though we have persevered through them all. This just goes to show you that, even though a piece of equipment can be very advanced, it will probably still need to be modified and played with to make it work correctly for your purpose.
As for things breaking, however, we have been lucky, since nothing has completely died. So far we have had to perform an oil change on the big compressor and replace its desiccant filters. We also do basic checks for chaffing and tightness on the equipment constantly, so we can hopefully catch something before it goes bad. There have also been some electronic problems with the small compressor, it has a tendency to turn off randomly, and issues retaining enough pressure in the big tanks to support 2000psi at a shot every 6 or 7 seconds. Other than these small issues, however, things are going swimmingly. We are a couple miles short of where we should be, as a result of the rainstorm and working on the streamer, but otherwise we are collecting a lot of really good data and that is what really matters. I’ll post again soon!
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