Anatomy of an IceBridge Mission
On Nov. 4, 2012, Operation IceBridge flew an 11-hour mission over the Recovery Glacier and Filchner Ice Shelf in eastern Antarctica. On the transit back home, NASA scientist John Sonntag gave a two-minute breakdown of the mission over the aircraft headset, including the purpose of the day’s flight, the challenges of working with Antarctic weather forecasts, and what the team found when they arrived on site. Credit:
NASA's Goddard Space Flight Center
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An 11-hour Operation IceBridge mission over Antarctica is not a casual undertaking. The mission planning starts months before as scientists weigh competing scientific objectives in order to design flights with the highest science value possible. And before making the actual journey, the IceBridge team has to carefully evaluate up-to-the-minute weather models to ensure success.
This year IceBridge flew 16 science flights over the Antarctic Ice Sheet, outlet glaciers, and the sea ice surrounding the continent. During one of those high-priority flights over the Recovery Glacier on Nov. 4, scientist John Sonntag gave a detailed description of how this mission was designed and the weather decisions that had to be made.
My name is John Sonntag. I’m a senior scientist with the ATM Team -- that’s Airborne Topographic Mapper.
Today’s mission was called the Recovery Offshore 01 mission. The name comes from the fact that it’s centered on the outflow of the Recovery Glacier, which is one of the major glaciers -- one of the major drainages -- in this part of the eastern Antarctica. Recovery, along with several of its neighbor glaciers, drains into the Filchner Ice Shelf, which itself ends up going into the Weddell Sea. The reason for the design of this flight today -- which, by the way, is made up of six parallel lines, more or less parallel to the outlet of the Recovery glacier -- six parallel lines spaced at 20 kilometers.
One of the main purposes of this mission is to use gravity measurements along with radar measurements to help determine the shape of the underwater cavity that lies beneath the Filchner Ice Shelf. That kind of thing is quite difficult to measure, especially remotely. One of the sort of classical ways of getting at the depth of the water beneath an ice shelf is to do seismic studies from the surface of the ice shelf. Those work quite well, but they have a drawback in that in order to cover very much distance with them, and they tend to be very, very time consuming and quite expensive. So we could do a version of the same thing using airborne gravity and airborne ice-sounding radar.
The reason that’s important is that the shape of the underwater cavity – well, let me back up a bit. The real reason it’s important is that it’s become clear to the glaciological community within the last couple of decades that much of the changes that we’re seeing worldwide, particularly in Antarctica and Greenland in these glaciers that come into contact with the ocean, is that the behavior of the ocean itself is highly linked with what’s going on with the glaciers.
What may be happening is that there’s some warming going on in the ocean waters, and as those warmer ocean waters come into contact with the front and the underside of these glaciers as they begin to float is that they sort of eat away at those glaciers, making them melt from underneath much faster than they can melt at the surface. And that tends to draw the glaciers down from the plateau much more quickly than would otherwise happen. That’s very hard to predict that kind of behavior, to model it numerically, unless we know what the shape of the cavity is under the water beneath the ice shelf.
Since that is such a difficult measurement to make, Operation Ice Bridge is ideally suited to make them because we have this aircraft that’s capable of flying very long distances and making very detailed, very precise measurements of a number of geophysical parameters, including the shape of these underwater cavities. So that’s the reason for the mission. When we decided to fly the mission this morning, the weather outlook for the region was probably not what you would call ideal for most missions. The reason it wasn’t ideal is because there were some clouds in the area.
Normally, we like very clear skies to do this type of survey, but there was something particular about the design of this mission that made it a bit more conducive to work with clouds – and that’s the fact that it’s over an ice shelf, which meant that it was not very far at all above sea level. With a number of our missions, we have to climb and descend up and down several thousand feet of terrain, which means that if you have any clouds at all that are as low as any part of the terrain is, they tend to make it difficult for us to fly the mission. This was not the case here because really the entire mission was flown within a couple hundred feet of sea level.
So we knew that there would be clouds surrounding the area, and when we flew in this morning, indeed there were around it. But there was also largely a hole in the clouds right where our survey was with the exception of one thin layer that was fairly high. I believe it was between eight and ten thousand feet in the forecast, and we knew that because this mission was mostly at sea level -- the ground was mostly at sea level beneath us -- the clouds that high would be well above the aircraft and would not present a problem for us.
You don’t always want to believe a weather forecast in that kind of detail, but we’ve had the benefit of some rather good weather models here, and also some rather knowledgeable professional meteorologists at the Punta Arenas airport that we consult with every morning before we fly. And so we developed over the years and over the course of this campaign a good sense of what kind of forecast we can believe and what are the kinds that we might want to sort of take a jaded eye with. The one this morning we knew we could believe, or we thought we could believe.
And when we got here this morning, sure enough, there was a thin layer of clouds between eight and ten thousand feet, which we were easily able to work underneath. And so it didn’t cause us any problems at all. Obviously, that gives us a lot of confidence for making similar decisions in the future for similar kinds of weather situations that may not be a total slam dunk. But in this case, we had good reason to believe that it would work out well, and sure enough, it did.
On the way in, we flew over an area that has been giving us quite a bit of problems with the weather, both in the accuracy of the forecasts and in the general character of the weather that’s there; that’s the Weddell Sea. In previous years, the Weddell Sea has not been terribly difficult for us to work in, but for reasons unknown to me, this year there have been persistent fairly well-organized low-pressure systems in the Weddell almost every day that we’ve looked. That’s caused us a number of problems in getting in here. Specifically, we haven’t been able to fly dedicated sea-ice mission in the Weddell.
So our transit in this morning took us in over part of the Antarctic Peninsula and over the extreme southern part of the Weddell, just in front of the Ronne Ice Shelf. And sure enough, most of it was clouded as the models predicted it would be. We could see bits of sea-ice surface here and there, and we took optical instrument data when we could. But for the most part, it was clouded as the models predicted it. When we made our descent into the Filchner Ice Shelf area, we could see the edge of the Ice Shelf and the edge of Berkner Island.
It was clear skies there, and just a beautiful, beautiful, beautiful scene with the low sun angle that you get down in these part casting a nice shadow where the front of the Ronne Ice Shelf meets the Weddell Sea, and also the edge of Berkner Island where it meets the sea and also where it meets the Filchner Ice Shelf; it makes a fairly dramatic scene, particularly with the sun behind it casting shadows. So a lovely flight overall.
NASA's Goddard Space Flight Center, Greenbelt, Md.