Research Interests

My interests go out to both remote sensing and field studies of past and present glaciations. My research focuses in particular on the polar regions. I am involved in several international research projects focused on monitoring changes in the cryosphere and their relation to climate.

Currently I work at ENVEO - Environmental Earth Observation - IT, an Innsbruck, Austria, based science and engineering company specialised in development and applications of satellite based Earth Observation for climate monitoring and cryosphere studies. I am a research scientist in several projects focused on determining changes in Arctic and Antarctic ice masses, among others the ESA funded projects: Antarctic Ice Sheet CCI, Greenland Icesheet CCI, Glaciers CCI, GlacAPI, STSE-CryoSat+ Mountain Glaciers, STSE-GLITter, STSE-Mass Balance, SAMBA and CryoTop Evolution. A recent BBC article highlights some of the work we do at ENVEO.

                                 Installation of permanent GPS station at Lonewolf nunatak, East Antarctica

Continuous monitoring of Greenland and Antarctic ice sheet velocities using Sentinel-1 SAR

The Sentinel-1 mission has opened up new opportunities for regular monitoring of glacier and ice sheet velocities at high spatial and temporal resolution. From January to March 2015 the first ice sheet wide campaign on Greenland was completed resulting in a nearly complete ice velocity map produced by ENVEO. Later that year the first Antarctic campaign commenced covering most of the continent outside the polar gap. Besides ice sheet wide campaigns the Sentinel-1 acquisition plan allows for nearly continuous monitoring of the Greenland ice sheet margin and several key regions in Antarctica at 12-day intervals. This offers the unique capability of operational monitoring of short-term and seasonal velocity fluctuations as well as year-to-year variations for large regions.

Greenland ice velocity from Sentinel-1

                                           Greenland ice velocity from Sentinel-1

Sentinel-1 carries a C-band synthetic aperture radar instrument providing high-resolution SAR images. Data is acquired across 250 km swaths at a spatial resolution of about 5 m x 20 m. We use repeat pass SLC images of Sentinel-1 acquired in Greenland and Antarctica to obtain ice flow velocity. We apply an iterative offset tracking approach, permitting to acquire the full range of velocities in a single swath while keeping the matching window at a minimum. Read more.....

Antarctic Peninsula ice velocity from Sentinel-1

                    Antarctic Peninsula ice velocity from Sentinel-1 (background Sentinel-1 amplitude image)

-------------------------------------

Other Research

GlacAPI aims at reducing the uncertainty of mass balance estimates of selected Antarctic Peninsula glaciers. The Antarctic Peninsula has shown a pronounced warming in recent decades that is considerably larger than the Antarctic and global average and perhaps constitutes as one of the fastest warming regions on Earth. The region underwent a series of rapid cryospheric changes in the last decades, most pronounced - and widely publicized in the media - the retreat of several large ice shelves that seemed to be linked to a series of exceptionally warm summers. The magnitude and abruptness of the events has spread concern as they seemed to confirm Mercer's (1978) prediction that they might be indicators of CO2 induced global warming.

Compilation of satellite images showing changes in areal extend of the ice shelves along the east coast of the Antarctic Peninsula since 1986. The ice shelf collapse is moving progressively southward towards the main continent.

In the wake of the ice shelf disintegrations their former tributary glaciers started to retreat, thin and accelerate with some showing an increase in flow speed of up to 5 times that during the pre-collapse period. These dynamical changes were initiated by a sudden reduction of resistive forces due to the ice shelf break ups. The acceleration causes dynamic thinning and leads to increasing ice export which contributes to sea level rise. The increased velocity on Drygalski Glacier - the largest tributary of the former Larsen A Ice Shelf - is still maintained more than a decade after the collapse. Glaciers draining into the former Larsen B Ice Shelf show a similar behaviour: years after the collapse the ice flow is still much faster and the perturbation, initiated at the ice front, has propagated upstream.

Although the Antarctic Peninsula itself does not hold enough ice for a significant contribution to sea level rise, the collapse events followed by the rapid dynamic response of their tributary glaciers have placed question marks on the stability of other ice shelves that fringe the continent and consequently on the stability of the glaciers that feed them. GlacAPI assesses recent temporal changes in the major glaciers formerly feeding the L-A, L-B and PGC ice shelves and will give refined estimates of their mass balance and contribution to global sea level rise. A second objective is to deliver a contribution towards a more thorough understanding of the dynamical processes that led up to the disintegrations and the subsequent acceleration of tributary glaciers. A thorough understanding of these processes is a prerequisite for assessing the potential future response of nearby regions buttressed by ice shelves to climate warming. Read more.....

-------------------------------------

Previously I worked at the Geophysics Laboratory of the University of Luxembourg, where I participated in a project to infer ice mass changes in Greenland using GPS measurements. Modern geodetic techniques that measure the contemporary mass balance of the Greenland Ice Sheet, such as satellite altimetry (e.g. ICESAT) and gravity (e.g. GRACE), must be corrected for postglacial rebound (PGR). In this project data from 40 continuously operating GPS receivers placed at the edge of the Greenland Ice Sheet are analysed. The GPS antennas are placed on metal rods that are anchored firmly in the bedrock. The instruments can measure the vertical uplift rate of the earth's crust very precisely. The GPS data is analysed and combined with gravity measurements to separate changes in crustal uplift resulting from PGR and present day ice mass changes. The results should contribute to better estimates of the current mass imbalance of the Greenland Ice Sheet. Read more.....

Greenland from space showing the locations of continuous GPS stations around the perimeter of the ice sheet.

-------------------------------------

My dissertation research, completed at Byrd Polar Research Center at The Ohio State University in 2006, focused on retrieval and analysis of ice flow velocity data using RADARSAT-1 imagery of Antarctica. More specifically, I used this data to investigate spatial and temporal variations in flow controlling factors, ice-marginal changes, mass balance and calving rates of Antarctica's major outlet glaciers through force-budget theory and various models. A PDF of my dissertation can be download here (19 Mb).

Recent observations show that some outlet glaciers in Greenland and Antarctica undergo rapid changes in flow velocity and ice thickness. There is concern about the implications of this for global sea levels and ocean circulation. At least part of the changes has been ascribed to changes in the dynamics of these glaciers. Measuring ice flow velocity and gradients in velocity are first steps in studying their dynamics and possible response to climatic changes.

The AMM-1 mosaic acquired as part of the RADARSAT-1 Antarctic Mapping Project (RAMP) projected on a digital elevation model of Antarctica

Ice flow velocity can be measured both in situ and using remote sensing. Most in situ methods currently rely on the use of either differential GPS surveys (DGPS) or optical surveys using a total station. In both approaches a network of stakes is set out on the glacier and repeatedly measured to estimate velocity. These methods work well for small mountain glaciers and over short periods of time. However, the sheer size of the Antarctic continent and the remoteness of the region make it very difficult, dangerous, impractical and expensive to determine flow velocity with a conventional glaciological approach. Apart from that, to further complicate the matter, nearby (stationary) fiducial points, which are often not readily available in the interior of Antarctica, are necessary to set up a reference frame. With the launch of the RADARSAT-1 satellite and the RADARSAT-1 Antarctic Mapping Project (RAMP) a great opportunity arose to derive ice flow velocity of Antarctica's glaciers remotely.

Flow velocities can be derived from sequential satellite imagery by means of feature tracking. Where repeat SAR data is available, orbits fall close enough, and coherence is preserved, velocity can also be determined using radar interferometry (InSAR). Only feature tracking is capable of acquiring velocity data over short (days) as well as long time spans (years to decades) and of fast flowing regions. In this approach, prominent surface features such as crevasses or rifts and edges (e.g. ice tongue edge) that move with approximately the same speed as the ice, and are identifiable on two co-registered images, are used to determine displacement and hence velocity.

The figure below shows an example velocity field of Brunt Ice Shelf (BIS) and Stancomb Wills Ice Tongue (SWIT) in Antarctica derived using feature tracking. SWIT is a fast-moving ice tongue that is fed by Stancomb-Wills Glacier and extends more then 225 km beyond its grounding line. The width at the ice front is approximately 70 km. BIS is seperated from SWIT by a large shear zone. It currently houses the British Halley VI station. We measure velocities of ~ 900 ma-1 on SWIT about 10km downstream of the grounding line. Velocity increases significantly downstream of the grounding line, but the velocity structure on the ice tongue is asymmetric. We find velocities up to 1350ma-1 on the northwest corner of the ice shelf, while the northeast corner shows maximum values of up to 1200 ma-1. Read more.....

Ice-flow velocity on the BIS and SWIT on the Caird Coast, East Antarctica (see inset). The velocity field is derived using feature tracking techniques on RADARSAT-1 images of 1997 and 2000 and represents a 3 year average. The map is compiled of more than 200 000 velocity data points with a pixel size of 400 m.

mouseover