Posted by: sioglac | Apr 17, 2014

Ground truthin’

I have to get something off my chest: I’m an observationalist. What does that mean? Well in my research, I make direct measurements of what a glacier is doing (for example, with a GPS unit) and use these observations to test hypotheses that I (or we as a community) have about the way glaciers work. In glaciology, observations are relatively rare (though this is changing!). It’s not easy to take a lot of observations of, say, Antarctica because Antarctica is: (a) really far away, (b) has a pretty rough climate to work in (coldest, highest, driest continent on Earth, or as every training I have ever taken says, it’s a harsh continent), and (c) is dark 24 hours a day, 6 months of the year. To that end, I consider myself extremely lucky to have an incredible set of observations that not only contains year-round data, but also contains multiple years of data. While related to the topic at hand, that’s just a tangent for this post.

One way I really like using what few measurements we have of Antarctica is to “ground truth” remotely-sensed observations (like from an airplane or, more often, a satellite up in space) or models. Remote sensing and models are incredible techniques we use in glaciology to understand how glaciers and ice sheets work on scales we could never cover with direct ground observation alone. Case in point: it takes (at least) 2 months of my time every year to make sure not quite two dozen GPS units are functioning well in a “logistically simple” (read: super easy) area of one ice stream in Antarctica—imagine how long it would take to instrument the whole ice stream, let alone the whole ice sheet. My Master’s advisor, however, instilled in me a healthy sense of skepticism about both remote sensing and models: fantastic tools if their methods are verified and their limitations are known. That, in a nutshell, is what ground truthing is. In other words, you can leverage a pretty limited (in both a time and a space sense) set of observations on the ground in Antarctica to test whether the observations satellites continually make are precise and accurate and/or whether the outputs from models are consistent with what the ice is doing in real life. In this way, you can take a relatively small set of difficult-to-make observations and use them to put your trust into methods that draw much broader conclusions than you ever could with your one, small dataset.

With that in mind, you can imagine how excited I get when a new issue of Journal of Glaciology comes out and I find a ground truthing study. [I’m borderline giddy when I find one; in other news, I’m a big ol’ nerd.] One article in the most recent issue easily takes the cake for best paper I’ve read in a long time. Seriously, how cool is this:

Screen shot 2014-04-17 at 10.03.51 AM

 

“As a second result, the upstream end point of the computed trajectory emerges very close to the glacier surface in 1926, giving a new and global validation of the glacier model in space and time.” How the authors managed to type that sentence without ending it with about a million exclamation points is beyond me. I also love that they tagged the article with the keyword, “glaciological model experiments.” As my aforementioned Master’s advisor responded when I emailed this article to him, “Tough way to validate a model… ‘So, I was wanting to validate my model, and wondered if you could help me…'” Sorry Bob. If I was only in for a Master’s with you, I don’t think I’d be ready for that kind of, um, commitment to model testing. But I do enthusiastically support this type of ground truth study!

The paper delves into the model in quite a bit of detail (A pretty good paper! Give it a read if you are so inclined.), so we’re going to skip to my favorite section:

Screen shot 2014-04-17 at 10.04.06 AM

A mystery remains!!

I have on many occasions used investigating a crime as a metaphor for how a glaciologist does his/her research. You use a very small set of clues to piece together a hypothesis, then use a slightly larger (though still extremely small) set of clues to test if your hypothesis is right. Jouvet and Funk blow my metaphor out of the water with the establishment of a new field: Forensic Glaciology**. I cannot wait for the day that I’m flipping through the channels on TV and find an episode of CSI that calls in some glaciologists to help them with their case. It’s going to happen and, to those of you in Hollywood, I happen to know a glaciologist down the road in San Diego who could make a guest-star appearance for you…

Give me a ring, CSI. I’m ready for my closeup!

**Yes, I know this isn’t the first time glaciology has been used to investigate corpses, but it is the first time (I think) corpses have been used to validate modeling work. See here for another fun example of forensic glaciology.

 

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Responses

  1. […] En annan studie som jag tyckte var intressant och som hade lokal anknytning till Alperna var den här: 1926 försvann tre alpinister i Schweiz och 2012 smälte deras kroppar fram i glaciären. Med […]


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