01Jan2015

Current Location: 50 N, 145 W

Happy New Year from Station Papa. My resolution for this year is to make a bunch of quality videos of whitecaps so that I can finish this PhD at some point. So far I am off to a great start! As a side note, I am a little bitter that with this cruise taking place over the new year, I will now have to start keeping track of “year” as a variable in all of my codes (the name of this post refers to the way the date gets represented in our files).

An unfortunate snafu while spooling line onto the winch last night resulted in an extra day spent on station today. Picture a rat’s nest made from a mile-long extension cord, and you wouldn’t be too far off. Fortunately for me, while all that was getting sorted out, I was able to take the day capturing some great video of the waves.

The video measurement strategy we are using now is called stereo video. The basic idea is this: when you take a picture of an object or a scene, you can’t really know the sizes or depths of anything in the photo. Your eye/brain combination is really good at using context clues to figure out that a photo is of, say, a 6 inch toy elephant and not the real thing, but those sorts of tasks are difficult to program into a computer. On the other hand, imagine taking two different pictures of the same scene, as though from left and right eyes. Now you can resolve the depth ambiguity, so long as you know the separation of the two cameras. You can test this for yourself: First, hold a finger out in front of your nose and take turns closing your left and right eye. Notice the way your finger “moves” relative to whatever is behind it in the background. Now hold your finger out an arms length from you, and repeat the eye switching. You should see that your finger moves less at the longer distance. That’s the basic idea behind stereo imaging — you figure out the depth of a picture by noting how much the objects in it “move” when glimpsed from a different angle. And of course there’s a lot of details and potential pitfalls that I am glossing over.

As you might imagine, the application of stereo video to waves is pretty powerful. If done correctly, a stereo camera system can fully reveal the three-dimensional structure of the wavy sea surface, at several frames per second. We are by no means the first person to make use of this method in studying waves, but we have some new ideas of what to do with these measurements that hopefully will prove fruitful. Seeing the data come in, I am very optimistic it will at least give us something to talk about.

– Mike

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