Tag Archives: NASA

Cockpit’s View of Greenland’s Glaciers, Ice-Sheets, and Sea-Ice

The glaciers and ice-sheets of Greenland retreat and melt in a warming world. Towering almost 3000 meters above sea level the ice-sheet is so thick and heavy that it depresses the bedrock underneath below current sea-level. Monitoring the ice-sheet, outlet glaciers, and sea ice of Greenland, NASA’s Operation IceBridge flies aircraft packed with radars, lasers, and optical sensors each spring and summer all over Greenland. There are exciting blogs written by the scientists aboard as they live and work out of Greenland. And today I discovered that they also provide video feeds as their plane conducts measurements. Here is an example from yesterday:

I am not entirely sure on the exact location off south-east Greenland, perhaps this is the area near Helheim Glacier, e.g.,

Greenland's bed-rock elevation from Bamber et al. (2003) digital elevation model based on remotely sensed surveys of the 1970ies and 1990ies gridded at 5 km resolution.

Greenland’s bed-rock elevation from Bamber et al. (2003) digital elevation model based on remotely sensed surveys of the 1970ies and 1990ies gridded at 5 km resolution.

but this will become clear as soon as the data are released to the public. This usually happens within a few months. The wide and open data distribution and access is one of the greatest things about this mission. If you want to see where the plane is now, this is the screenshot I took just now (site)

Locations of NASA's P3 air plane near Jacobshavn Isbrae on April-10, 2013.

Locations of NASA’s P3 air plane near Jacobshavn Isbrae on April-10, 2013.

The evolution of Jacobshavn Isbrae retreat from 1851 through present. [From NASA's Earth Observatory]

The evolution of Jacobshavn Isbrae retreat from 1851 through present. [From NASA’s Earth Observatory]

Jacobshavn lost its buttressing ice-shelf during the last decade and now rapidly discharges ice from the Greenland ice-sheet directly into the ocean at a rapid rate. Most likely, the ice-shelf was melted by the ocean from below (Holland et al., 2008). This type of accelerated discharge raises global sea-level, because ice previously sitting on Greenland’s bedrock moves into the ocean where it eventually will melt. In response to the ice removed, the bed-rock rises as there is less mass above it to hold it down (Khan et al, 2010). All this has actually been measured by satellites (mass-loss) and ground-based GPS (bed-rock response). We live in a dynamic and rapidly changing world where our sensors and software show new patterns of physics that have never been seen before. There is so much more to discover …

Csatho, B., Schenk, T., Van Der Veen, C., & Krabill, W. (2008). Intermittent thinning of Jakobshavn Isbræ, West Greenland, since the Little Ice Age Journal of Glaciology, 54 (184), 131-144 DOI: 10.3189/002214308784409035

Holland, D., Thomas, R., de Young, B., Ribergaard, M., & Lyberth, B. (2008). Acceleration of Jakobshavn Isbræ triggered by warm subsurface ocean waters Nature Geoscience, 1 (10), 659-664 DOI: 10.1038/ngeo316

Khan, S., Wahr, J., Bevis, M., Velicogna, I., & Kendrick, E. (2010). Spread of ice mass loss into northwest Greenland observed by GRACE and GPS Geophysical Research Letters, 37 (6) DOI: 10.1029/2010GL042460

Shots of Airborne Lasers at Petermann Gletscher, Greenland

If shots of whiskey make you dizzy, shots of laser stun. NASA stunned me this week, when I discovered that they provide millions such shots of Greenland from which to construct detailed images of the landscape. The shots are free, no age-limit. This is better than the usual remote sensing or photography of “just” brightness. The laser gives us height, and not just the perception of it by shadows and fake angles of illumination, but hard and direct measurements of, well, height above sea level. Have a look at several million such shots of Petermann Gletscher taken in 2010 before the glacier broke to Manhattan-sized pieces:

Petermann Glacier surface elevation from laser shots on Mar.-24, 2010 at the site where the Manhattan-sized ice island formed Aug.-6, 2010. The background shows the same scene at the same time at 250-m resolution from MODIS (see below). Colors along the 350-m wide laser track line show height above sea level in meters.

Petermann Glacier on March 24, 2010 as seen from MODIS satellite at 250-m resolution with two flight tracks along which laser data are collected. The black box shows the site of the figure above. The color figure on the right shows the slope or gradients of the data shown on left. It emphasizes regions where brightness changes fast. Multivariate calculus is useful!

We see two tracks: the one on right (east) has the ice stick more than 20-m above sea level (yellow colors) while about a mile to left (west) the ice’s surface elevation is only 10-m above sea level (light blue). Since the ice is floating and densities of ice and water are known, we can invert this height into an ice thickness. Independent radar measurements from the same track prove that this “hydrostatic” force balance holds, the glacier is indeed floating, so, multiply surface elevation by 10 and you got a good estimate of ice thickness. The dark blue colors of thin ice show meandering rivers and streams, ponds and undulations, as well as a rift or hairline fracture from east to west. This rift is visible both in the right and left track, it is the line along which the glacier will break to form the 2010 ice island. All ice towards the top of this rift has long left the glacier and some of it has hit Newfoundland as seen from the International Space Station by astronaut Ron Garan:

Last remnant of Petermann Ice Island 2010-A as seen from the International Space Station on Aug.-29, 2011 when it was about 3.5 km wide and 3 km long [Photo credit: Ron Garan, NASA]

Both are images of Petermann ice. The photo measures the brightness that hits the lens, but the laser measures both brightness and ice thickness. The laser acts like flash photography: When it is dark, we use a flash to provide the light to make the object “bright.” Now imagine that your camera also measures the time between the flash leaving your camera and brightness from a reflecting object to return it. What you think happens at an instant actually takes time as light travels fast, but not infinitely fast. So you need a very exact clock to measure the distance from your camera to the object. Replace the flash of the camera with a laser, replace the lens of your camera with a light detector and a timer, place the device on a plane, and you got yourself an airborne topographic altimeter. So, what use is there for this besides making pretty and geeky pictures?

The laser documents some of the change in “climate change.” Greenland’s glaciers and ice-sheets are retreating and shrinking. Measuring the surface and bottom of the ice over Greenland with lasers and radars gives ice thickness. The survey lines above were flown in 2002, 2003, 2007, 2010, and 2011. These data are a direct and accurate measure on how much ice is lost or gained at Petermann Gletscher and what is causing it. My bet is on the oceans which in Nares Strait and Petermann Fjord have increased the last 10 years to melt the floating glacier from below.

There is more, but Mia Zapata of the Gits sings hard of “Another Shot of Whiskey.” What a voice …

ResearchBlogging.org

Johnson, H., Münchow, A., Falkner, K., & Melling, H. (2011). Ocean circulation and properties in Petermann Fjord, Greenland Journal of Geophysical Research, 116 (C1) DOI: 10.1029/2010JC006519

Krabill, W., Abdalati, W., Frederick, E., Manizade, S., Martin, C., Sonntag, J., Swift, R., Thomas, R., & Yungel, J. (2002). Aircraft laser altimetry measurement of elevation changes of the greenland ice sheet: technique and accuracy assessment Journal of Geodynamics, 34 (3-4), 357-376 DOI: 10.1016/S0264-3707(02)00040-6

Münchow, A., Falkner, K., Melling, H., Rabe, B., & Johnson, H. (2011). Ocean Warming of Nares Strait Bottom Waters off Northwest Greenland, 2003–2009 Oceanography, 24 (3), 114-123 DOI: 10.5670/oceanog.2011.62

Thomas, R., Frederick, E., Krabill, W., Manizade, S., & Martin, C. (2009). Recent changes on Greenland outlet glaciers Journal of Glaciology, 55 (189), 147-162 DOI: 10.3189/002214309788608958

Science Writing: George Orwell and Richard Garvine

How to write, read, and review as part of large science teams when millions of dollars are at stake? Writing and reviewing science projects for the National Aeronautical and Space Agency and the National Science Foundation, I came up with a list of 6 loose rules that make for good science proposal writing:

1. Think about your audience, as the message is conveyed best, if the reading is fun;
2. Avoid technical detail, cite the peer-reviewed paper instead;
3. Present and explain the big picture concisely and accurately in engaging ways;
4. Less is more. Focus on the why, not the how;
5. Avoid shady ambiguity, convoluted arguments, and incomplete explanations;
6. If it can’t be said simply, don’t say it.

This list then reminded me of a short essay that George Orwell wrote in 1946 titled “Politics and the English Language.” It concludes with these 6 rules:

(i) Never use a metaphor, simile, or other figure of speech which you are used to seeing in print.
(ii) Never use a long word where a short one will do.
(iii) If it is possible to cut a word out, always cut it out.
(iv) Never use the passive where you can use the active.
(v) Never use a foreign phrase, a scientific word, or a jargon word if you can think of an everyday English equivalent.
(vi) Break any of these rules sooner than say anything outright barbarous.

I read the essay in the spring of 1989 when I spent much time at sea with Richard Garvine. Rich was my PhD advisor and he probably suggested this essay to me, his German graduate student with poor writing skills. Rich taught me both science and writing. I miss him.

Richard Garvine in his office at the University of Delaware in the 1990ies.

Petermann Glacier Shape and Melt Channels

Radars, lasers, and fancy computers all shape the way we see the shape of glaciers. An airplane flies along a line down the glacier with (1) a good GPS. It carries (2) a vertical laser that measures the distance from the plane to the surface below while (3) an ice-penetrating radar measures where the ice meets the ocean. All these data are distributed freely by the University of Kansas’ Center for Remote Sensing of Ice Sheets (CReSIS) that is part of NASA’s Operation IceBridge.

March-24, 2010 view of Petermann Glacier from NASA’s DC-8 aircraft. Photo credit goes to Michael Studinger of NASA’s IceBridge program who also blogged about this flight.

From CReSIS I gathered the data from Petermann Glacier before its break-up in 2010 and 2012. I show two flight tracks on a MODIS map for the same day that NASA’s DC-8 was collecting the shape data. There are two tracks as the airplane flies along the fjord out towards the ocean, turns, and flies back up inland. The seaward (red) track is slightly offset from the landward (black) track.

Petermann Glacier on March 24, 2010 from MODIS. The left panel shows the reflectance while the right panel shows the magnitude of the spatial gradient of this signal. Red and black dots are the flight tracks from which the shape of the glacier was measured by radar flown on a DC-8. The dark black line indicates where the glacier is grounded to bed rock ~500 meters below sea-level. The 3 boxes indicate location where the floating ice shelf terminated before 2010 (top box), after 2010 (middle box), and now (bottom box) due to the 2010 and 2012 ice islands. Top left are clouds, mountain shadows on left also.

The laser gives us the top surface of the ice while the radar gives us the bottom surface. Connect these two and we get ice thickness. Below I show how these ice elevations change along the glacier. The ocean is to the right near 65 km while the grounding line of the glacier is near -20 km, so the part of the glacier that is floating on the ocean was about 80 km in 2010, that’s about 50 miles. Now why is the red shape so different from the black line?

Shape of Petermann Glacier’s floating ice shelf on March 24, 2010 (top panel) and ice thickness (bottom panel). Radar data from University of Kansas, Center for Remote Sensing of Ice Sheets (CReSIS) with EGM2008 geoid corrections applied by me.

Well, the two tracks were NOT the same and these data show that the glacier varies in thickness and shape at small scales. The floating ice-sheet has lots of topography. It has hills, valleys, channels, and troughs. It stuns me to see how long and how steep this one specific channel is: it changes by almost 200 meters in 2 km. That’s huge. We do not fully understand how these channels form, why they are there, if they change over time, or perhaps most importantly, how do they relate to the stability of this or other glaciers. A first theoreticial PhD thesis was recently submitted by Carl Gladish. It is thought-provoking, but it does not settle the issue. We do not even know how many such channels there are, but there are ideas on how to perhaps do this with data both in hand and more to be collected.

Simplifying future analyses, I changed my Petermann MODIS and CReSIS co-ordinate system from latitude and longitude to a distance in kilometers along and across the glacier. The standard MODIS “color” (lets call this f) varies as one walks the glacier in its along-stream (call this x) and across-stream (call this y) directions. The color f is a function of x and y which scientists write as f=f(x,y). Now compare this color f(x,y) with the SPATIAL CHANGE (call this the slopes) of color that I show in the right panel. The MODIS data are the same, but why do they look so different in the two panels?

Well, the slopes draw the eye to smaller scale features in the right panel. This technique sharpens edges, fronts, and small spatial irregularities that our eyes tend to skip over. Our brains are trained to integrate and to condense information looking for the largest patterns first. So, taking the difference between adjacent values to get slopes and shapes, I do exactly the opposite and make sure that small irregularities stand out:

Close-up of March 24, 2010 MODIS image from the grounding line (black line at bottom) to the location of the present seaward front of the glacier (black box at top).

Notice the many stripes along the glacier near the bottom (x=0) right (y=80) near where the red triangle is. I believe these structures relate to sub-surface melt-channels of intense ice-ocean interactions, but belief is not truth and as scientists we must proof our believes and truths in ways that other people can check by repeating the experiments or calculations. There is so much more fun work to do, but, sadly, there are only 24 hours to a day.

Oh, and a (British) submarine is perhaps on the way to dive under this ice-shelf to take a close look and lots of data of under-ice topography, temperature, salinity, and bottom topography, if we can get a ship and experiment to get it there. So much work to do … [to be continued]

Steensby Gletscher Sheds 10 km^2 Ice Island

Following the rapid southward motion of Petermann’s 2012 Ice Island (PII-2012) via MODIS satellite imagery, I noticed a larger piece of Steensby Gletscher nearby breaking off. Steensby discharges into Sankt George Fjord whose upper reaches are narrower than Petermann’s (4.5 km vs. 15.5 km wide). The new ice island is smaller than the Manhattan-sized ice islands from Petermann, but it is still about three times the size of Manhattan’s Central Park (~ 10 km^2).

Steensby Gletscher and Sankt George Fjord on Aug.-15 and Aug.-24, 2012 (top) and fjords and glaciers of north-west Greenland facing the Arctic Ocean as seen by MODIS-Aqua on Aug.-24, 2012 13:45 UTC (bottom). All data are shown at 250-m spatial resolution. Note the segment of Steensby Gletscher which is separating from the glacier to form a new ice island.

The floating ice shelf of Steensby Gletscher is also two to three times thicker, but it moves more slowly. It appears, that a lateral crack or rift broke off sometime between Aug.-21 and Aug.-22, 2012 to form the ice island, this one about 1/10 the size of PII-2012. This latest calving is about 7 years of steady advance of this glacier. Comparing the front of the glacier with that observed in 1947, 1953, and 1971, I find its current site well within the earlier bounds reported by Dr. Anthony Higgins of the Geological Survey of Greenland. The same cannot be said for Petermann Gletscher about 40 nautical miles to the south-west. Unlike Petermann’s Ice Islands, Steensby’s are likely to linger and stay inside its fjord for several years as many of those calving from neighboring Ryder and C.H. Ostenfeld Gletschers do.

Michael Studinger of NASA’s IceBridge project provides stunning aerial photography of Steensby Gletscher when he flew over North-West Greenland in May of 2011.

Addendum 8-25: Mauri Pelto posted equally stunning high-resolution Landsat imagery and provides more context, analyses, and references.

Higgins, A.K., 1990: North Greenland glacier velocities and calf ice production. Polarforschung, 60, 1-23.