Today we began our journey down the upper Mississippi River. This section is above
the confluence of the Mississippi River and the Ohio River where they join at Cairo,
IL. We met the M/V Strong, the Corps of Engineers buoy tender, in Cape Girardeau,
MO. Tony Johnston is its captain and was the captain during our last survey in 2008.
The research team is near the same as last time with Drs. Beatrice Magnani (principle
investigator (PI)) and Brian Waldron (co-PI) from the University of Memphis and Dr.
Kirk McIntosh (PI) and Steffen Saustrup (technician) from the University of Texas
at Austin. New to the research team are students Lei Guo (pronounced Lay-Go, but in
China the proper way to address someone is last name first so Go-Lay) and Xenia (“X”
sounds like a “S”) Fave. Lei Guo is a doctoral student at the University of Memphis
and Xenia is an intern with IRIS, but attends the Florida Institute of Technology
as an undergrad.
Welcome to our team and our daily travel log.
Once aboard the Strong we immediately began setting up the equipment and testing connections.
This took about 2-3 hours. The generator was started. It supplies power to the compressors
that fills the air tanks to 2000 psi (that’s 136 times normal atmospheric pressure!).
We’re not scuba diving. The compressed air travels from the front of the boat to the
back through what we call the umbilical to the pneumatic sound source. When the sound
source is deployed into the river and the air released, energy is sent into the water,
through the riverbed and deep into the ground. What energy is reflected off geologic
layers deep in the ground returns to the water surface and is picked up by our streamer
that has 24 sensitive pressure devices called hydrophones. The returned energy information
is recorded on computers giving us a glimpse into the subsurface structure over 0.5
miles to 1 mile deep. Really cool.
Anyway, we worked quickly to get everything ready for deployment. Once the research
equipment was tested and everything securely fastened, we deployed our equipment.
Things at first were tricky. Though we tested our equipment on deck, we wanted to
test it in the water. To do this the Strong held its position in the water. Now the
upper Mississippi River is rising due to the large snow melts up north. When the river
rises, its waters extend onto the banks and into the surrounding landscape. Debris
such as old fallen trees that had come to rest during a falling river stage are picked
up again by the river and transported downstream. So, a tree got caught on the Chirp.
The Chirp is a single channel device akin to depth sonar on a boat. With this Chirp,
we can image in high resolution the upper 50 ft below the river bottom. Luckily the
Chirp was help in place by the Strong’s 15-ton crane so after some finagling we got
the tree loose. Unfortunately the tree snagged our tail buoy on the streamer that’s
towed 300 feet behind the Strong, snapping lose the buoy. So the tail buoy had to
be retrieved and reattached.
Our problem with the river debris lessened once we began our drift backwards. Now
for those not familiar with the first survey, we found that drifting backwards reduced
the noise on the equipment traveling through the water thereby helping us see deep
into the ground with greater clarity. So the Corps of Engineers is awesome. Their
pilots turn their boat to point upstream, and back down the river with in essence
a 300 ft trailer (the deployed streamer) while having to navigate debris, buoys, dikes,
and of course barge traffic.
I must stop here as it’s nearly midnight and we have a long day ahead of us. You have
a gist of what we’re doing and how things are going. Please check back with us regularly
to see what new things are going on. Later.