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GeoTalk: Using satellites to unravel the secrets of our planet’s polar regions

GeoTalk: Using satellites to unravel the secrets of our planet’s polar regions

Geotalk is a regular feature highlighting early career researchers and their work. In this interview we speak to Bert Wouters, a polar scientist at the University of Utrecht, and winner of one of the 2016 Arne Richter Awards for Outstanding Young Scientists. At a time when the polar regions are facing increasing challenges resulting from climate change, understanding how they might respond to them is crucial. Bert’s PhD research using satellite data (from the GRACE mission) set a benchmark for the analysis and interpretation of data like it. As his career has advanced, Bert has made contributions to a number of fields within the polar sciences, from ice-sheet research, glacier and ice-cap mass-balance studies, through to ocean modeling and climate prediction. It is this notable breadth of knowledge, accompanied by an impressive publication record which makes Bert a worthy awardee.

First, could you introduce yourself and tell us a little more about your career path so far?

I was born and raised in Belgium, but moved to the Netherlands to study aerospace enginieering at the TU Delft when I was eightteen. During my PhD there, I focused on the use of satellite gravity data for climate science. Back then, the GRACE satellites had been in orbit for only a couple of years, and people were still learning how to handle and interpret this completely new set of data. The observations contained a lot more noise than expected before launch and one of the first things I did was to develop a method to remove this noise. Once we managed to do so, it opened up a whole new world. For the first time, we could track the movement of water mass on the Earth surface from month to month. These were certainly exciting times! My supervisor gave me the freedom to do pursue my own interests and I used the GRACE data to study many different topics, ranging from hydrology to oceanography and solid earth science. In the last year of my PhD, I focused on the cryosphere, which is still my main field of research.

After graduating, I did have the opportunity to continue in geodesy, but I felt it might be better for my overall development to step out of my comfort zone and move to a different field. I started a post-doc at the Dutch meteorological office (KNMI), with the aim of improving predictions of the Atlantic meridional overturning circulation. This is part of the global ocean conveyor belt and transports heat around the Earth. It has an important impact on the climate in the Atlantic region (think The day after tomorrow, minus the Hollywood drama) and my job was to predict its behaviour on decadal time scales using a global climate model. The first year was pretty though, but I learned a lot about the complexity of climate physics and numerical modeling, and I still profit from this experience today.

Meet Bert!

In 2012, I was awarded an ERC Marie Curie-Skłodowska fellowship and moved the University of Colorado in Boulder for 2 years to work with John Wahr. He was one of the founding fathers of the GRACE mission and a true giant in the field of geodesy. I had not met him before I started my fellowship, but he turned out to be not only a great scientist, but also one of the kindest and friendly persons I have ever met. I continued to refine my GRACE methods for monitoring of the cryosphere, but also started looking at different types of remote sensing data, in particular height measurements made by the Cryosat-2 altimetry mission.

This satellite had only been launched 2 years before and data was being released bit by bit.It gave me a great drive to be among a select group of people having a first look at these new observations. In the last year of my fellowship, I worked at the University of Bristol with Jonathan Bamber (the  EGU’s current  vice-president) to further refine the Cryosat-2 processing and combine it with the GRACE data. The combination of two independent measurements provides a powerful tool to map the ongoing changes in the cryosphere and yielded in some very exciting results.

Since November 2015, I’m a post-doc at the Institute for Marine and Atmospheric Research (IMAU, Utrecht University), renowned for their modelling of the regional processes (snowfall, melt, etcetera) on ice sheets and glaciers. Such models, together with in-situ observations, are indispensible to understand the changes we are seeing in the satellite data.

During EGU 2016, you gave a talk which focused on melting of glaciers and ice-caps in the North Atlantic. During the talk you spoke about the implication such melting might have on global sea level rise. Could you tell us a little more about your findings?

It’s a well known fact that the ice sheets of Greenland and Antarctica are losing ice. Studies about these regions usually receive a lot of attention from the media and general public, and rightly so: they contain a huge reservoir of ice and will be one of the major contributors to sea level rise in the coming centuries.

But we shouldn’t forget about the smaller ice caps and glaciers in other parts of the world. Many of them are located in regions which are experiencing rapid warming and because of their small size and the delicate balance between snowfall and melt that shapes them, they are extremely vulnerable to changes in the local climate. The GRACE and Cryosat-2 data show that glaciers in the North-Atlantic region currently contribute as much to sea-level rise as the Antarctic ice sheet and will continue to do so in the future. In fact, models indicate that some of the ice caps are already beyond a point of no return and that glaciers and ice caps will be one of the major sources of sea level rise in the coming decades.

Why have the glaciers and ice-caps of the North  Atlantic region received such little attention, at least until now, considering the potentially large impact their melting can have on global sea levels?

Tthe Devon Ice Cap, located in eastern Devon Island, Nunavut, Canada is one of the North Atlantic region ice-caps which have received little attention.

Well, of course I’m not the first to study these glaciers and ice caps. In fact, some individual glaciers have been monitored for over a hundred years. These records are extremely valuable and vital for validating and interpreting satellite observations, and already showed that many glaciers are retreating.

However, taking in-situ measurements on a glacier is a challenging job, and often expensive, so these observations are generally made on small glaciers, which tend to be located in easily accessible locations with a maritime climate.  This means that the few hundreds of glaciers that are monitored on a regular basis are not necessarily representative for the roughly 200 000 glaciers world wide. We really need satellite observations for that. So maybe one of the reasons that they have received little attention is because we just didn’t know how bad things are until recently.

Another reason is that their big brothers, Antarctica and Greenland, pose a huge threat, too, especially when considering longer, millenial, time scales. There’s only so much research funding out there, so in a way it makes sense that the scientific community focused on this first when global warming came into the picture.

A common theme throughout your research has been using satellite data and geodesy to unravel the secrets of our planet’s polar regions and oceans. What attracted you to this particular branch of the Earth sciences?

To be honest, I ended up in this field more or less haphazardly, it wasn’t part of a grand master plan I had when I started university. Back then, my main interest lay in aerodynamics, but by the time I had to choose a topic for my master thesis, I couldn’t imagine myself working on that for the rest of my life. When one of my supervisors suggested I work on remote sensing of sea level rise, it felt as if it was the right thing to do and that’s how it all started.
Having said that, as a kid, I was fascinated by two things: science, inspired by a nutty professor in my favorite comic books, and nature (around the age of six, I started a club together with a friend to save the planet) and in a way I’m combining these two things in my present job. So maybe I was just destined for this after all…

Also, at a time where travel has almost become a commodity to most people, I find it fascinating that there are still places on Earth where no one has ever set foot and which we can only study using remote sensing. Its very intriguing and almost a privilige to be able to map these places at an ever increasing level of detail, especially with all the dramatic changes that are now going on in the polar regions.

Quoting the late Gordon Hamilton: “Every time I open up a satellite image the potential is there for something astonishing to have happened since the last time I looked.” That sums up pretty well what makes this job so exciting, I think.

The Grace satellites in action. Credit: NASA JPL.

It’s clear that satellite data is invaluable when it comes to understanding changes on our planet. How do the GRACE and Cyosat satellites help in that effort?

GRACE is the only mission that can directly weigh the ice caps and glaciers, but it has a very coarse resolution, typically a few hundreds of kilometres. It helps to track the changes in ice mass on a regional scale, but that’s far too low to identify individual ice caps or glaciers. Cryosat-2 allows us to do so, but it measures height changes, and certain assumptions need to be made to translate this to mass changes, which can be verified against the GRACE observations. So these two missions nicely compliment each other.

Thank you for talking to us Bert. We’ll round-off this interview with a final question about careers. As a researcher who has made huge advances in this field, what advice would you give to someone who wants to pursue research in the field of geodesy and remote sensing, particularly when it comes to focusing on the planet’s polar regions?

Keep an open mind and don’t be afraid to stray outside your  own research field! Everything is connected in climate science, the polar regions aren’t an isolated system and to understand what’s going on and how to optimally use the satellite data, a basic knowledge of climate physics helps a lot.

Many problems we’re facing in geodesy and remote sensing also pop up in other fields, in a slightly different way and often other people have already found a solution to your problem. For example, to filter out the noise in the GRACE data, I used a method that’s commonly applied in atmospheric science. My second advice would be: collaborate! The problems we’re facing are so complex that it’s impossible to solve everything on your own. Interact with other scientists, within and outside your own field, it pays off.

And don’t be afraid to share your data and preliminary results with others. There’s a lot of pressure, especially on starting scientists, to publish as much as possible which sometimes makes it tempting to keep your data to yourself. But many times, other people have that piece of data that would make your study so much more interesting. And if someone else publishes a paper on something you’re working on, don’t hold any grudges, but try to find a different angle to it and do better. There’s some much to study, and science shouldn’t be about competition, but about collaboration.

Geotalk is a regular feature highlighting early career researchers and their work.

Geosciences Column: A new rock outcrop map and area estimation for the entire Antarctic continent

Geosciences Column: A new rock outcrop map and area estimation for the entire Antarctic continent

Antarctica has been known as “the frozen continent” for almost as long as we have known of its existence. It may be the only place on Earth where, instead of information on the extent of glaciers or ice caps, there exists a dataset of all non-icy areas compiled from satellite imagery.

However, this repository is far from perfect: while satellite resolution and coverage have been steadily improving, Antarctica is challenging ground for remote sensing. Ice and cloud cover can be difficult to tell apart, and the low position of the sun in the sky means that long shadows can make snow, ice and rock very difficult to distinguish. As a result, the estimates of the ice-free proportion of the Antarctic continent have been vague, ranging from “less than 1%” to 0.4%.

In a new paper published in the journal The Cryosphere, scientists from British Antarctic Survey and the University of Birmingham show that the continent is even icier than previously thought. Using imagery from NASA’s Landsat 8 satellite, they find that just 0.18% of the continent are ice-free – less than half of previous estimates. This equates to an area roughly the size of Wales on a continent half again as big as Canada.

Lead author Alex Burton-Johnson and his colleagues have developed a new method of accurately distinguishing between ice, rock, clouds and liquid water on Antarctic satellite imagery. Because of the challenging nature of classifying Antarctic satellite imagery, the researchers used only the highest-quality images: they were mostly taken in midsummer, when the sun describes the highest arc in the sky and shadows are smallest, and on days with low cloud cover.

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(Left) The blue squares represent the coverage of the 249 satellite images the researchers used, showing that most rocky areas in Antarctica are clustered along the coastline. The images overlap in many places, allowing for more accurate classification where some clouds occur in pictures. (Right) The new dataset for rock outcrops covers all areas marked in red. The NASA Landsat 8 satellite does not cover areas south of 82°40′ South. Islands such as South Georgia and the South Orkney Islands are too consistently cloudy during the summer period, so the new method cannot be applied here. From : Burton-Johnson et al. (2016).

The huge thickness of the Antarctic ice sheet – more than 4,000m in some places – made the scientists’ job easier: they could exclude large parts of the continent where not even the tallest peaks come close to the ice surface. A total of 249 suitably high-quality images covered those parts of the Antarctic continent that have rock outcrops.

A few locations, however, are too extreme for the new image classification method. Some of the South Orkney Islands and the subantarctic island of South Georgia are covered in heavy cloud for so much of the time even in summer that the researchers could not apply their new method. Here, they had to rely on the older dataset. They also had to exclude parts of the rugged but remote Transantarctic Mountains from the study as the Landsat 8 satellite only covers areas north of 82°40’S.

The code for the new classification methodology is available on GitHub, so that enthusiastic remote sensers can try their hand at further improving it or simply admire the frozen beauty of Antarctica from above.

By Jonathan Fuhrmann

References

Burton-Johnson, A., Black, M., Fretwell, P. T., and Kaluza-Gilbert, J.: An automated methodology for differentiating rock from snow, clouds and sea in Antarctica from Landsat 8 imagery: a new rock outcrop map and area estimation for the entire Antarctic continent, The Cryosphere, 10, 1665-1677, doi:10.5194/tc-10-1665-2016, 2016.

Imaggeo on Mondays: Plate it up – a recipe for sea ice errors

Last week, a team of cryospheric scientists published a paper in The Cryosphere that showed how tiny plates of ice can lead to spurious estimates of sea ice thickness. This week, we’re featuring their findings, as well as some spectacular sea ice images in the latest in our Imaggeo on Mondays series…

Viewing the poles from above is a stunning sight – a seemingly endless expanse of brilliant white, ridged blue crests, and delicate grey fringes that stretch like lace over the ocean. Such a vantage point also allows scientists to get to grips with what’s happening to these delegate fringes, seeing how far the sea ice stretches from year to year and how its thickness changes over time.

One of the best ways to measure how thick a large expanse of sea ice is, is to measure its elevation, comparing it to the level of the surrounding water to see just how much is floating on the ocean. This can be done swiftly using satellites, which have the added bonus of keeping a continuous record of change over time. But recent research reveals there may be a problem with this technique.

Spying on sea ice from some 20,000 feet above the surface. (Credit: NASA)

Spying on sea ice from some 20,000 feet above the surface. (Credit: NASA)

Beneath sea ice you find a fine crystalline mush composed of thin ice crystals, or platelets. These platelets bridge the boundary between sea ice and the sea below. Because ice is buoyant, this icy mush (aka the sub-ice platelet layer) pushes the sheet of sea ice upwards, increasing its elevation. Small differences in the proportion of platelets below the ice could make it appear thicker than it really is, leading to inaccurate measures of sea ice thickness.

Looking out over Antarctic sea ice. (Credit: Andrew Chiverton via imaggeo.egu.eu)

Looking out over Antarctic sea ice. (Credit: Andrew Chiverton via imaggeo.egu.eu)

To know just how big a difference these platelets make, first you need to know how much solid ice is present in the mush. Using drill hole data collected in 2011, a team of scientists from New Zealand and Canada estimated that solid platelets made up about 16% of the mush beneath Antarctic sea ice. It may not sound much, but this many platelets could cause ice thickness to be overestimated by almost 20%.

You also need to know just how dense the platelets are. If they have a very low density, they can buoy the ice up more, and if they’re denser, they will have less of an affect on sea ice thickness. The findings mean a fair bit of ground-truthing will be needed to get better estimates of sea ice thickness from satellites in the future.

By Sara Mynott, EGU Communications Officer

Reference:

Price, D., Rack, W., Langhorne, P. J., Haas, C., Leonard, G., and Barnsdale, K.: The sub-ice platelet layer and its influence on freeboard to thickness conversion of Antarctic sea ice, The Cryosphere, 8, 1031-1039, 2014.

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.