How Gliders Work: A Look Inside the Blue Hen

Earlier this week the glider team pulled in the University of Delaware’s glider, nicknamed the “Blue Hen,” from the ocean. They needed to change its batteries and download one of the instrument’s data. But they didn’t want to miss what was happening out at sea, so they pulled what they call a “Nascar turnaround,” working like a pit crew to get the work done overnight.

It gave us an opportunity to look at the inside of a glider and explore how these complicated robots manage to go where they’re told and collect the data we need, practically by themselves.

To fly, a glider needs a few basic abilities: it needs to be able to control its buoyancy so that it can either sink or rise; it needs to know where it is and where it’s going; it needs to be able to call home for new instructions; and it needs to be able to collect data. And it has to do all this with only a small allowance of space, weight, and battery power. Click through the slideshow to see how gliders manage it:

photocrati gallery

ironcrossThe stream of data that comes back from the gliders every hour or so is what allows the CONVERGE team to be adaptive in their sampling. With a research ship or an instrument fixed on the seafloor, it’s difficult to change your plans as you get more information. But changing a glider’s plans is as simple as uploading a new instruction file.

Over the last couple of weeks the team has settled on a sampling plan they’re calling the “iron cross.” Each of the three gliders takes a different part of the cross (see the map), and together they reveal what the waters of the Palmer Deep are doing. The Blue Hen (blue on the map) flies to the center of the cross and just goes up and down in the same spot. The glider from the University of Alaska, Fairbanks (green), flies a straight line along the length of the Palmer Deep canyon. The Rutgers RU05 glider (red), flies across the canyon.

RU05 goes at right angles to the Alaska glider, and those two gliders cross at the spot where the Blue Hen is working. Altogether, this gives the scientists a way to separate out ways the water conditions could changing.

temperature profiles from a glider at Palmer Station, AntarcticaHere’s an example of the data they’re collecting, and why it helps to have data from more than one glider. This graph shows one round trip of the Alaska glider from the northeast end of its route, down to the southwest end, and back. The dashed line shows where the glider turned around—the two parts are different lengths because it took longer to fly out to the dashed line than to fly back. That’s because it was fighting the current in the left section of the graph; then it turned around and rode with the current.

The graph shows the temperature of the water as the glider flew up and down on its way. Do you see any differences? First of all, it’s interesting that the water is warmer at the surface and at the bottom (orange colors), and coldest in the middle (blue colors). This is because the sun has warmed the waters at the surface; the middle waters are still cold from winter; and the deepest waters represent a deep current that has brought in warmer water underneath it all. Layering of different water types is a very common feature in the ocean.

Now look at the left and right edges of the graph. Remember that the glider was doing a round trip, so these two parts of the graph represent the same patch of water at the northeast end of its route. On the left side compared to the right side, there’s less warm water at the surface and the colder middle water doesn’t extend as deep.

This is an interesting development, but it leaves the scientists with a problem: did the water change in temperature between the glider’s first pass and its second pass? Or did a current carry in different water, with a different temperature (as well as other characteristics) and push the original water out of the way? With only one glider taking measurements, it would be hard to figure this out. But with three gliders working the same stretch of water from different angles, they’re much more likely to be able to put together the answer.

Huge thanks to Laura Palmara for putting the map and data plot together for this post.

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22 Responses to How Gliders Work: A Look Inside the Blue Hen

  1. Jalen January 26, 2015 at 9:43 am #

    The Glider is very fascinating!

  2. Qwalee showers January 26, 2015 at 11:35 am #

    Why cant you just find the krill and follow it?

    • Hugh Powell January 26, 2015 at 8:33 pm #

      Hi Qwalee – Interesting question. If you’re asking why don’t the gliders find the krill and follow it, the answer is sometimes they do. The glider pilots sometimes decide to stick with a patch of water they’re interested in and keep sampling it over and over again, floating wherever the water takes it. However, scientists are always want to measure many different examples of whatever they’re interested in. This helps them be sure that they’re learning about the average rather than just finding out about one example. For example, if you wanted to know how big human beings were, you’d probably want to measure more than just one person in your class. You’d want to measure people from all over town, all over the state, all over the country, and so on. For the same reason, the scientists don’t want to study just one patch of krill the whole time they’re here. Thanks for asking – Hugh

  3. Rachel & Valeria January 26, 2015 at 11:58 am #

    With the data that you’ve collected from the moorings, gliders, fluorescence sensors, acoustic sensors, HF radars, and satellite tags. How are food webs affected by local experiences like tides and the temperature of the water?

    • Hugh Powell January 26, 2015 at 8:28 pm #

      Hi Rachel & Valeria – great question! This is what the entire Project CONVERGE team is trying to figure out with this project! Right now they’ve collected a ton of data, but they’ll need to spend the next year or two analyzing the data before they can tell you for sure. – Hugh

  4. Majd January 26, 2015 at 12:44 pm #

    Do plankton have trouble developing under salt conditions?

    • Hugh Powell January 26, 2015 at 8:15 pm #

      Hi Majd – phytoplankton in the ocean are adapted to live in saltwater, so they don’t have trouble developing in salty water, at least within the range of saltiness that they encounter in the ocean. Thanks for asking – Hugh

  5. Mark January 27, 2015 at 3:24 pm #

    Does the glider frequently have problems with marine life, and if so what are the most problematic ones ?

    • Hugh Powell February 2, 2015 at 11:57 am #

      Hi Mark – gliders have problems with marine life only occasionally. The biggest problems are when marine organisms attach themselves to the glider. This happens when gliders are left in the water for several months, and they can get things like barnacles growing on them. In warm waters, they also sometimes have problems with fish called remoras. These strange fish usually cling on and hitch a ride on the sides of large fish such as sharks, but they will also do this with gliders. The reason this is a problem is that the glider needs to operate at a very specific weight. If something starts growing on the glider, the added weight can cause the glider to sink and not be able to come back up. Thanks for asking – Hugh

  6. Katherine January 27, 2015 at 3:39 pm #

    Why did you nickname the glider ” Blue Hen”. How many gliders are usually needed for trips? How long does it usually take to build a glider?

    • Hugh Powell February 2, 2015 at 11:53 am #

      Hi Katherine – take another look at photograph #7 in this blog post and read the caption—it describes where the name “Blue Hen” comes from. A single glider can operate on its own, but for larger projects it helps to have more than one. Project CONVERGE uses three gliders, and two more are in nearby waters doing related work. I’m not sure how long it takes to manufacture a glider from scratch, but it takes from a half-day to a day to open up a glider, replace the batteries, download files, rebalance and test its buoyancy, and put it back together. Thanks for asking – Hugh

  7. Brianna January 27, 2015 at 4:50 pm #

    Wow! This must have been an interesting experience!

  8. Keanu January 27, 2015 at 5:25 pm #

    How does the glider control its own buoyancy

    • Hugh Powell February 2, 2015 at 11:50 am #

      Hi Keanu – Have another look at the second photograph in this blog post and read the caption—it describes the basics of how the glider controls its buoyancy. Then let us know if you have more questions. Thanks – Hugh

  9. amarachi January 28, 2015 at 4:17 pm #

    I saw a video about the glider. It’s amazing how it works and how it can connect to a satellite dish all the way from the water.

  10. Trent January 28, 2015 at 4:36 pm #

    I think it is very interesting how the gliders work

  11. Nicolette January 29, 2015 at 9:38 am #

    This must be an intresting and fun project!

  12. Ms. Dunbar January 29, 2015 at 3:35 pm #

    We’ve been watching a video by Tina Haskins that talks about a “yo” or when the glider goes down and then back up. The question came up, “Where did that word come from?” We thought maybe Josh Kohut may know.

    • Hugh Powell January 31, 2015 at 6:30 pm #

      Hi Ms. Dunbar – I believe that they are referring to the glider going up and down like a yo-yo (or possibly like a yo-yo being played with by someone walking at about half a mile an hour 🙂 So one trip down and up could be called a “yo.” Thanks for asking – Hugh

  13. Naomi Weintraub January 29, 2015 at 9:06 pm #

    Chavez you found any data that has been unexpected?

    • Hugh Powell January 31, 2015 at 6:28 pm #

      Hi Naomi. Good question – when you do science, you’re looking at the unknown, and it turns out that most of the data you find are unexpected in one way or another. (It’s been said that most great discoveries are preceded by someone saying “hm, that’s strange.”) Here it’s been no different. One of the big unexpected patterns in the data so far has been learning that the convergence zones that form here shift around very quickly—we’ll have more about that finding in a few days. Thanks for asking, Hugh

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