Time is flying! We are well into our third week at sea and I realized I haven’t even explained what it is I am in charge of on this cruise. I apologize, but my days (nights?) have been busy with getting some paper revisions and edits done. With those almost finished it is definitely time for another blog post.
So I am here as the sole person in charge of the LADCP or Lowered Acoustic Doppler Current Profiler. These instruments are attached to the CTD rosette frame (Rosie) and use the Doppler effect of sound waves to measure the speed of water throughout the water column. These instruments are very common in oceanographic work and can also be used in an anchored setup on the seafloor as well as mounted on seawalls or bridge pilings in rivers and canals. Ships also frequently have ADCPs attached to their hulls, which allow them to take constant current measurements as the boat moves.
In our case, we lower the instruments to the ocean floor in order to get a complete profile of the water column. There are 2 LADCP instruments on the platform- one that looks downward (the master) and one that points upward (the slave) as well as a battery pack that provides the instruments with power during their nearly 4 hour ocean voyage at each sampling station. When the instruments are on deck between stations they, and the battery, are connected to the ship’s power through a train of long black cables.
In our case, we lower the instruments to the ocean floor in order to get a complete profile of the water column. There are 2 LADCP instruments on the platform- one that looks downward (the master) and one that points upward (the slave) as well as a battery pack that provides the instruments with power during their nearly 4 hour ocean voyage at each sampling station. When the instruments are on deck between stations they, and the battery, are connected to the ship’s power through a train of long black cables.
So what do I do? About 15 minutes before we reach the sampling station, I go into the lab adjacent to the sampling bay and begin the process of getting these instruments up and running in preparation for their next dive into the water. I check their status, erase their current files to make room for new data, and then get them all set to go. They start “ping-ing” and a few minutes later they are in the water. The ADCP measures water currents with sound using the principles of the Doppler effect. Sound waves have a higher frequency when they move toward you than when they move away from you. The ADCP works by transmitting “pings” at a constant frequency while it is in the water. As the sound waves travel, they ricochet off particles suspended in the moving water and are reflected back to the instrument. These waves reflected off of a particle moving away from the instrument send back a slightly lowered frequency, while particles moving toward the instrument send back slightly higher frequency waves. The difference between what gets sent out and what the instrument receives is called the Doppler shift. The instrument uses this shift to calculate how fast the particle and the water around it are moving. |
When the instruments get back on deck I reconnect power to them and the battery and begin downloading the precious data they hold. Some immediate QC is done to ensure things look good (cables haven’t gone bad, the battery is providing sufficient power, etc). Later, I process the data to see what kinds of currents we are seeing in the water. Sometimes this shows that I need to swap out an instrument (no small feat as they are quite heavy and awkward, but I have now done it 3 times and consider myself “capable”). Currently we have a Master that is operating with only 3 of its 4 beams operational. This is ok- redundancy is key in these types of instruments and they are able to work with just 3 beams, but no less. I also just replaced our uplooker and installed our alternate instrument. It seems to be working well (the one I took off was also down to 3 out of 4 working beams). All in a days work for the LADCP operator!
As we get closer and closer to the equator the weather is definitely warming up and quite humid. We have had a couple days of intense rain which makes for crabbiness onboard as we are even more confined to the indoors. Overall, everything is going smoothly and there are few complaints. I spend my free time reading (currently reading The Martian) and enjoying the sunset at the start of my shift. I’ve managed to figure out an eating schedule and always have at least a plate of leftovers ready to go in the fridge. My current guilty pleasure is popcorn in the evenings. Thanks for following along! Until next time…. |