Profiling Floats by Chanelle
I have been traveling around Tasmania a couple of days now,
but the reality of the upcoming S04P cruise didn’t entirely set in until I saw
the R/V Palmer docked in Hobart
yesterday afternoon. As an undergraduate who works at the University of
Washington Argo float lab, I always see the instruments from our lab get
shipped to these places all over the world, but I never thought I would one day
be able to go with them.
Our lab builds over 100 floats a year as part of the Argo
program, which is an international collaboration to better understand the
world’s oceans with a global array of profiling floats. There are 32
participating countries in the program, and collectively over 3000 floats have
been deployed. Argo floats are autonomous sensor platforms that measure the
salinity and depth of the upper 2000 meters of the water column. They are
distributed throughout the world’s oceans and the data collected from the
floats has increased the understanding of global scale circulation and improved
climate models and predictions.
In addition to constructing floats for the traditional Argo
array, our lab also builds floats for the SOCCOM project, which stands for
Southern Ocean Carbon and Climate Observations and Modeling. The Southern
Ocean is a particularly important study region because this ocean is
responsible for a large amount of sequestration of carbon dioxide and heat from
the atmosphere. Additionally, this region is projected to be particularly
impacted by ocean acidification. However, despite the importance of the
Southern Ocean to global climate and its vulnerability to ocean acidification,
this region is poorly understood because of its inaccessibility for much of the
year. The goal of the SOCCOM project is to use a network of autonomous
profiling floats throughout the Southern Ocean to collect data up to 2000
meters depth year round. This data will be used to better understand this
region and create better projections and models of Earth’s climate and the
ocean’s biogeochemistry.
The floats built for the SOCCOM project are outfitted with
additional biogeochemical sensors that measure nitrate, chlorophyll, dissolved
oxygen, and pH. There will be 6 SOCCOM floats deployed on the Palmer from our lab. The last time I saw
these floats, I was putting them in crates for their long voyage to Hobart.
Before the floats were ready for shipment, though, they had been in the lab for
months being prepared and undergoing countless quality checks.
The first step that I as an undergraduate technician did in
helping prepare these SOCCOM floats for deployment was performing pressure
calibration tests on them. I use a deadweight tester to exert pressure on the
sensors, and I make sure that the pressures being read by the sensors are
within a certain range of what they should be reading. Usually, the readings
are within range, but occasionally I get readings that are out of
specification, so I send the CTD head (the part of the float that houses the
salinity, temperature, and depth sensors) back to an oceanographic instrument
facility called Seabird to be recalibrated. This process ensures that the
floats that are deployed will have accurate readings of their depth.
Another quality check I perform on the floats is telemetry
testing of the SIM cards. When the
floats are in the middle of the ocean, they transmit their data back to shore
via satellite, which they do with SIM cards that are similar to what you have
in your cell phone. Before the SIM cards are installed in the floats, I make
sure they are able to connect to satellites and to both of our lab computers
via both an internet connection and a modem to modem connection.
My next task is to prepare the floats for ballasting. Since
the floats take profiles up to 2000 meters of depth, they must be made to be
neutrally buoyant at this depth through a process called ballasting. This
process involves putting them in a pressure vessel and determining what weight
needs to be added to the float in order to make it neutrally buoyant at depth.
I do not do any of the ballasting, but I make sure the floats are ready for it
by temporarily mounting the FLBB (sensor that measures chlorophyll) at the top
of the float where it will be out of the way while in the pressure vessel.
Once the ballasting is done, we know how much weight needs
to be added to the float, which is achieved with a combination of battery packs
and strips of lead. Once the float has
been all built up with the correct amount of weight, I perform buoyancy checks
on the floats to ensure that they are weighted correctly. This consists of me
putting the floats in a test tank located in the UW Oceanography building and
ensuring that the floats are able to return to the surface. Once the float gets
back to the surface, I push it around to make sure it is able to correct itself
and is sitting correctly in the water.
After the buoyancy check is complete, we put the floats
through “dock testing” where we put the floats outside and let them go through
mission sequences. This is our final run through to make sure everything is
running properly and that the float is able to connect to the satellites and
transmit files. After this check, the float is pretty much ready to go and be
crated for shipment. At this point, my work is usually done with the float, but
now I am lucky enough to have the opportunity to participate in the deployment
process of these S04P floats.
The tasks I described are just a few of the things I do at
the lab, and this post has barely scratched the surface of what our lab does
and the greater Argo and SOCCOM programs. I am grateful to have worked with a
fantastic cohort of people at the UW Argo float lab and to be a part of a program
that is doing so much to help better our understanding of the ocean. I’m looking forward to continuing my work with
these instruments while on S04P.
Do the floats have to come up to the surface to transmit their data to the satellites?
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