Monday, March 27, 2017

Searching the Sea

Finding anything at sea is a tricky business. The antenna on our EM-APEX floats only sticks up about a foot above the water, and often sinks below the surface when a wave passes by. Without accurate GPS positions, finding the floats would be impossible, but even when we know exactly where they are it can take some time to see them in the waves.

We brought out a total of 25 EM-APEX and have been deploying them in tightly-packed clusters to sample the ocean's small-scale horizontal variability and how it evolves in time. But after we are finished in one location we need to round them all up. Then the hunt begins.

Keaton Snyder, Avery Snyder, and First Mate Eric Piper on the lookout for EM-APEX floats. (photo credit: James Girton) 

There's a float in this photo. Can you find it? (photo credit: JG)

Once spotted, the challenge is to maneuver the ship carefully up to the tiny float in the water and bring it into range of the hooking poles near the back of the ship without running it over. This is especially tricky when the float carries fragile instruments on top. In addition to the antenna and CTD, which are relatively sturdy, about half of our EM-APEX floats carry temperature microstructure sensors for measuring turbulent mixing. The tiny glass thermistor bead on the top of these can be broken with even a light brush of the hand, let alone being bashed against the side of the ship. Needless to say, we brought spares, but as of this posting (about 3/4 of the way through the cruise) we haven't broken any! Our success is likely a combination of skill (in ship driving and hook-wielding), experience (knowing what methods have been successful in the past, as well as easing cautiously into any new procedures), and, of course, luck (in both the favorable weather on our recovery days, as well as in the way the waves and ship happened to line up during that final approach and grab). You never know what the ocean will throw your way, but it pays to be prepared.

Captain Diego Mello and First Mate Eric Piper steer the ship for an EM-APEX pickup. (photo credit: JG)
Field engineers Avery Snyder and Eric Boget prepare to snag the EM-APEX. (photo credit: JG)

Caught! With the snap hook around the
lifting loops, the EM-APEX is ready to be
brought on board. (photo credit: JG)
Safe on board (including the microstructure
probes--tiny glass beads on top of metal stalks
on the gray cylinder at the top end of the float).
(photo credit: JG)

On our first big float recovery day, we even had calm enough wind and wave conditions that we were able to put in one of the small boats that the Sikuliaq carries. This makes recovery much easier, since two people can lift the float out of the water by hand. We had planned to alternate pickups, but the boat was able to speed ahead of the Sikuliaq and pick up all 7 remaining floats before the ship could even reach one!

The workboat with a load of
EM-APEX. (photo credit: JG)
When conditions allow, the Sikuliaq's workboat
provides a quicker way to pick up multiple floats.
(photo credit: JG)

1 comment:

  1. Adapt and conquer- the height of the Sikuliaq allows spotting, while the work boat is less unwieldy. Saves a lot of time, even with the launch, I'd imagine. Cheers and safe voyage!