Overview of the Observational Research of Helheim Glacier in Greenland
Introduction
Over the course of the semester I have been doing observational research on Helheim Glacier in Greenland. I’ve been working with Catherine Walker and Brittany Schmidt in the department of Earth and Atmospheric Sciences at Georgia Institute of Technology. The purpose of this research is to understand the relationship between the crevasse (fractures in ice) patterns, glacier flow, and calving rate (this is the speed that the front of the glacier breaks off). High resolution satellite images, of years between 2001 and 2014, were used to trace the crevasses in the ice electronically for further modeling. This is an informal review of the work I have done this semester of spring 2015. I will discuss my process, results, observations/conclusions, and the future work planned.
Overview of Glaciers
Glaciers are giant rivers of ice that are formed by the accumulation and compaction of snow. Gravity drives it downward like a slow moving liquid. Glaciers form on mountains or near the poles. In Antarctica and Greenland contain 70% of the world’s fresh water supply, and if melted, they would raise the sea level by 70 m. The grounding line is the point where the glacier leaves the land and begins floating on water. The calving front is at the end of the glacier, and this is where giant blocks of ice break off, known as calving. This leads to the glacier losing large amounts of its ice overtime. “The physics of ice sheets” was the source used to gather this information.
Procedure and Apparatus
My overall process has stayed the same since I began but has been refined. The first three images I did were 2001, 2003, and 2005 gathered from the ASTER imaging instrument, but these had already been done by Catherine. The purpose of these first three images was to see if the process was replicable and to compare our results.
My first impressions
I briefly saw Catherine’s drawings before I began working on my own. However, I did not look at in depth or while I worked on my own. Seeing it, I remembered thinking how time consuming it must have been to create given the level of apparent detail. Therefore, it drove me to constantly question whether or not I was being detailed enough, and I ended up drawing as much detail as I could. My first image turned out more detailed than Catherine’s, but I still wondered if the higher detail may have been the result of unwarranted assumptions that may negatively impact the model. The only way to complete such a tasking project is to make certain assumptions along the way. Otherwise, I’d never had finished. I’ll try to explain these assumptions later. After I completed the first image, we could discuss how and where I was doing it wrong. Except, what I did seemed fine. Catherine processed my image, and the model she made essentially matched what she did. So, I have kept to the same logic for the rest of the images I did.
Beginning work on the first image
For the first image, I thought it would be beneficial to adjust the image brightness, contrast, and resolution in Photoshop. I thought this would make it easier to make out the faint crevasses in the ice, but I found this to be more of a hindrance than of any real help. Parts of the image were dark and difficult to make out, and increasing the resolution size did not improve the actual image quality. All it did was blow up what was already there and increased the file size along with it. The larger file size, in turn, made it the application I was using more prone to lagging.
The application I used was already a little slow to respond. I had decided against using Photoshop on my laptop even though it seemed like the best option. The level of detail required seemed like it would be overly arduous on my computer. I found a program to use on my iPad. This would be more like tracing on a sheet of paper, so it would be quicker and easier. The program was Bluebeam Revu, shown in Figure 1.
Figure 1. Snapshot of Bluebeam Revu iOS App
The program worked well enough but lagged a lot, and I made more mistakes because of it. Normally, I’d undo it. Then I’d redraw it, but I learned to accept a certain level of inaccuracies because it was tedious to constantly have to undo and redo. It made it difficult, but I tried to trace with as much detail as possible. I zoomed in to more precisely trace the crevasses, and I zoomed out so the image wasn’t to distorted to make out the next crevasse. This means I zoom in and out for each line to make sure it’s precise but still accurate. That app had to reprocess the image each time, only perpetuating the lag. It would register the starting point and the ending point. Rather than registering the curves, sometimes it formed a straight line. I began to try and make smaller lines to overcome this, but in some places, the image lacks the finer curvature details.
After completing the first image, I made a point to find a different app. I found GoodReader for iOS, shown in Figure 2, and it works a lot better. It quickly and smoothly zooms in and out and is relatively easy to operate. I’ve used it for all of the other images. I think it has led to clearer, more detailed, images, so the 2001 image may be less accurate from using the Bluebeam application.
Figure 2. A snapshot of GoodReader in iOS.
Assumptions in Completing the images
Even with the more efficient app, I kept using the smaller lines most of the time. Figure 3 shows an excerpt from the 2010 image in the center of the glacier near the calving front. Here you can see how several crevasses appear to be continuations of others. I try to look at these as independent lines because there are spots in the image that make it seem like the crevasse stops. The individual lines should still model to represent the same overall contour.
Figure 3. Excerpt from 2010 near the calving front.
The crevasses were interpreted as the darker portions of the image. This assumption may be wrong. The dark may only be the shadow of the shapes, but it should have a negligible effect on distorting the overall shape of a crevasse. In which case, I assumed it to be a relatively accurate representation of the general shape and length of the crevasses. I must admit, I don’t fully understand how to distinguish what is a crevasse. Early on I looked at Google Earth to get a better idea of the glacier structure. Figure 4 is a close up with a scale at 2000 ft at the bottom right of the image.
Figure 4. A google earth screenshot of the Helheim glacier at around the same resolution as in the ASTER images
This is roughly equivalent to the ASTER image resolutions. I interpret the dark portions as crevasses. However, Google Earth offers a higher resolution than what is seen in the ASTER images. Figure 5 shows the glacier with a scale at 200 ft shown at the bottom right.
Figure 5. The Helheim glacier at roughly 10 times the resolution of the ASTER images.
At roughly ten times the resolution of Figure 4, the darker regions look less like a crevasse. It’s more like this is a flatland of dirty snow with giant white mountains protruding through it. I don’t know what to make of it. Nevertheless, Figure 4 seems to demonstrate a clear set of crevasses. Even if what I interpret as crevasses are in fact something else, I think they are related to the crevasses such that they should convey the same overall shape of the crevasse contours.
The crevasses did not always appear as clear as in Figure 4. Along the margins and further up away from the calving front, the glacier appears far less distinct. In these areas, I used a lot of small lines again to try and make out what appeared to be faint shades of crevasses. In these areas, the lines appear noisier with a less distinct pattern. This may be a characteristic of the glacier, or it may be a result of my trying to find a pattern or crevasse where there is none. Even if a pattern does exist, I cannot say with confidence that it was not by bias of expecting a particular pattern that lead to my tendency to create one. I do not fully understand how this model is being tested, but I wonder if there is a way to compare results with and without these areas included to see if there is a significant improvement or loss in model accuracy. I suppose this also leads to the question of whether the added detail I try to include significantly improved the model. Am I better off doing a rougher estimation of the crevasses like Catherine? It could save time, and it may even lead to more accurate, if less precise, results.
Figure 7. Here is a portion of the 2003 Helheim Glacier image. It is taken from the bottom curve of the Glacier without the fracture lines drawn over it.
Figure 8. Here is a portion of the 2003 Helheim Glacier image. It is taken from the bottom curve of the Glacier and it includes the fracture lines drawn over it.
Consider Figures 7 and 8. These are cropped images of the 2003 image of the Helheim glacier with and without the lines I drew. The outcrop is taken from the lower portion of the glacier where the smaller glacier flows into Helheim. Looking back at Figure 8, I can see some of the lines that I left out. I’ll try to explain this as well as possible. I interpret the slightly darker areas within the white-blue as crevasses. Looking at it with the black lines makes it difficult to gage them against one another. I may have over looked these, but it may also be that I deemed them insignificant compared to the other lines. On some level, once I reached a certain density of lines, I moved on. The center portion, with its larger fractures, had finer details to be drawn, but there is a point where these details take away from the overall model in these areas. I suppose I sought to convey the best level of detail on the highest level discernable. Sometimes, the level was lower with a focus on the finest of details and others it was higher with a focus on the overall features of the glacier.
I don’t mean to contradict myself, but this sort of logic can be difficult to implement. I would often start, stop, and then return later. It would be like looking at Figure 8 after the fact with the more prominent crevasses already drawn, but it is hard to avoid. A lot the time, it’s difficult to go from the center to the fainter margins. Other times, I would be dissatisfied with fainter regions because there would be a lot of blank space, so I’d return to it later with fresh eyes. In doing so, I may be directly overriding the system that I talked about above. I try to keep this in mind whenever I think the most intense areas, like the center, has more to add. Although in the fainter regions, it seems less important because the apparent variations in crevasse intensities are less significant.
As I mentioned before, I interpret the darker areas as crevasses. They seem like impressions in the ice. Sometimes, the lines appear to flow into another creating a large imprint. I interpret these to be like roots branching off from one another. This is may ingrain a certain level of bias. I try to use the shape of the other lines that are more apparent to infer how these fainter, more chaotic, regions become to look like they do.
Figure 9. Here is an example of how I would draw some of the more obscure features on the Glacier. This image is the same as the one shown in Figure 7.
Figure 9 was created using Figure 7. It’s the same section of the 2003 image of Helheim, but I’ve focused in one a few areas to try and demonstrate what I explained in the last paragraph. I’ve circled three areas to use as an example. Below the image, I show the impression I see in the ice (a) and what fracture I might draw from it (b). The drawing orientation is the same as in the image. In the circle marked 1, you can make out an impression in the ice. 1a shows what impression I see. Notice there is a small divide between the middle arm and the right arm. 1b shows how I might draw this piece. I did this example on my computer which was difficult to trace with, and that middle arm was supposed to connect into one not branch off like that. However, my point is to demonstrate how I infer that there are three branching fractures there despite the fact that the left and middle arms don’t appear to have a divide separating them. In the circle marked 2, there is a similar situation. 2a shows the rough impression I see in the ice, and I then interpret it as two arms branching apart. The same is with number 3. These blotchy areas are not too uncommon, and I it seems like the best way to infer a pattern out of them. I try to use the surrounding features to consider the overall shape of the fracture or fractures. Then I try to consider what pattern would best fit the area and its surrounding. The finer details of these areas are largely subjective, but I think the general shape remains the same. That is why I think this type of assumption is appropriate.
If you compare these examples to Figure 8 you don’t see exactly the same thing. That was a while back, and my thought processes have changed. Although, it is worth nothing that I don’t always see something the same way. I don’t want to overthink I (more than I already do). Sometimes I may see a branch like that in Figure 9 as independent lines that don’t connect. I think it still forms the same general shape.
I think it necessary to explain these assumptions so that they can be considered when the images are modeled. These are all potential sources of error. If there is a better way to approach it I’d like to know, but the process was largely up to me to make. I had to come up with some sort methodology to go by. This seemed reasonable.
Results
Overall
There are clear flow patterns within the ice that are obvious when viewing on a large scale, but upon closer look the crevasses become more sporadic. The more subtle the crevasse the more difficult it was to make out. This may lead to a slightly less accurate model. The most distinct fractures exist in the center of the glacier, and it lessens toward the glacier margins. This may not be directly apparent in the models because there was no way to distinguish depth and overall size when tracing. However, the margins tended exhibit a larger amount of noise; the fractures did not always appear to follow any specific direction. What is clear, along the margins, is a type of sandwiching effect on the crevasses. This was more evident along the inner curve, or northerner, margins. The margins along the outer curve were less noticeable. These were the most difficult to trace because it was difficult to distinguish the crevasses. The outer curve has a smaller flow of ice coming into it which may allow these margins to translate its stress into the smaller flow rather than be concentrated by the margin walls. Where the rock margin returns, the crevasses become more prominent. As it approaches the calving front of the glacier, the ice has the highest amount of crevasses with several crossing into a matrix like shape. Finally, the calving front tends to form into a concave like shape. I have some ideas why these things may happen, but I’m hesitant to state them because I’m not sure I understand the dynamics enough. Still, these stand to tell a lot about the glacier dynamics with the proper analysis.
The next sections will refer to each year. These will list figures that are attached in full resolution. This attachment has them all organized and labeled, but I’ve also linked to each folder of images that I have as I talk about them below.
2001
The 2001 Helheim glacier with lines is in Figure 10, and just the lines are shown in Figure 11. The first thing to notice with this image is the color and brightness. I already mentioned that I adjusted it for the first image. I was very meticulous with this; I included literally every crevasse I thought I could see even those in the smaller glaciers flowing into Helheim. I later realized I didn’t need to do this, so I didn’t pay as much attention to them in the future. Figure 11 doesn’t include these because I had to clean up the occasional line that had been drawn off to the side accidently, so I figured I’d make this image the same as the others. I’m still amazed at how well it turned out. It made it easier for the future images because it showed where it was all going. I think one of the big things here is there are a lot of straight lines (not most but more than desired). As I said earlier this fails to convey the finer details. One thing I notice is that I drew a lot more horizontal crevasses in this image than future images. This may be a result of being slightly less concerned about getting every tiny thing. However, the other years have a calving point that is further up, so this may be something that happens more as it stretches further over the water without. It definitely shows the glacier at its highest amount of snow and ice of the years looked at. Nevertheless, I’ll be paying closer attention to this region in the future to see if I’ve been overlooking it.
2003
Figures 12 and 13 show the 2003 glacier. It clearly has less ice and snow cover than the 2001 image, and the calving front is further up. I still drew the smaller glacier for this one. It may be a coincidence but there is a chunk of lines that appear slightly denser than other areas. This is towards the middle of the image. It is directly above where the smaller glacier enters and above the portion against the margin where the empty space separating the two flows ends. It may be the interaction of these three different flows that leads to extra stress in this specific region, but why then doesn’t it exist in the 2001 glacier?
2005
Figures 14 and 15 show the 2005 glacier. There was cloud cover for this image, so the upper portion of the glacier was too difficult to make out. When I realized it was still okay to model was when I realized some of the details weren’t important, like the smaller glacier which I didn’t complete all the way.
2007 – August
Figures 16 and 17 show the 2007 glacier. This was the first image from the Earth Explorer. I found 2013 and later following the instructions that Catherine gave me. That left 2006-2012, so I tried other sources in Earth Explorer. I found 2007 and 2010. They both read the same resolution, but they ended up being lower than described. 2007 was the worst. The lines for this image are far less dense than the other images. It should still convey the same picture, but with less detail. There wasn’t an obvious change in the calving front for the glacier between 2005 and 2007.
2010 – June
Figure 18 shows the 2010 glacier. I haven’t completed it yet, but I’ve included the image as is. It was lower resolution than 2001, 2003, and 2005, but much more than 2007. I don’t think this one will be nearly as bad.
Future
Five images have been completed, and the next set to be done are 2006, 2012, 2013, 2014, and maybe 2004. These are the other ASTER images. Follow the hyperlinks to see these images. There is also a 2008 image, but it has too much cloud cover. I have another 2010 as well, but it doesn’t look any better than the one I already did. In fact, all of these images look slightly smaller than the original three (about the same resolution as 2010 shown in Figure 18). I think these will be as doable as the 2010 image. My biggest concern is that the grey distorts worst when zoomed in than the past images. I didn’t find anything better on Earth Explorer, and I’ll have to deal with what I have.
For the Love of Science 