Conference Agenda

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Session Overview
Session
Session 4D - Ice-caps and Glaciers
Time:
Thursday, 23/Mar/2017:
4:10pm - 5:50pm

Session Chair: Helen Amanda Fricker
Session Chair: Jonathan Bamber

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Presentations
4:10pm - 4:30pm

Invited - Keynote: Monitoring and Modelling Glacier Changes in Western Canada

Shawn Marshall1, Brian Menounos2

1University of Calgary, Canada; 2UNBC

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4:30pm - 4:50pm

Near Real-Time Mass Balance of Arctic Ice Caps from the CryoSat-2 Radar Altimeter

David Burgess1, Laurence Gray2, Luke Copland2

1Natural Resources Canada, Canada; 2University of Ottawa

Canada is a circumpolar nation which
collectively holds the largest reserve of land ice on the planet outside of the
ice sheets of Greenland and Antarctica. Since the early
1960’s, reference glaciers in the Queen Elizabeth Islands (QEI) have been
measured annually to provide a multi-decadal time series of glacier mass
balance as an indicator of climate change. Unprecedented warming across this
region since the early 2000’s has resulted in strongly negative glacier mass
balances, causing this region to become the largest non-ice sheet contributor
to eustatic sea level rise. This recent shift towards strongly negative mass
balance, combined with predictions of enhanced warming for the Arctic to at
least 2100 (IPCC), has increased demand for more timely information pertaining
to annual glacier mass balance from the Arctic region. In this study we present
seasonal height changes of the Meighen, Devon, and Barnes ice caps in the
Canadian Arctic using CryoSat-2 SARIn mode ‘Point of Closest Approach’ (POCA)measurements. Independent validation through comparison with in-situ mass balance and NASA ATM data highlights the effectiveness of CryoSat-2 for obtaining near-real time glacier mass balance information from one of the fastest warming regions on Earth.


4:50pm - 5:10pm

Validation of CryoSat-2 for Elevation-Change Detection Over Glaciers on Svalbard and Ice Rises in Antarctica

Geir Moholdt, Laurence Gray, Thorben Dunse, Kirsty Langley, Kenichi Matsuoka, Thomas V. Schuler, Bert Wouters

Norwegian Polar Institute, Norway

Precise applications of CryoSat-2 over glaciers and ice sheets can be hampered by variable signal penetration and backscatter in snow and ice, particularly during the transition from a cold winter snowpack to a melt-affected summer snowpack. In this study, we use dense networks of GPS surface profiles to validate CryoSat-2 elevation estimates from ESA's Level 2 product and alternative processing techniques using Level 1b data. We consider surface elevations from both the point-of-closest-approach (POCA) and the full swath of the interferometric mode. We investigate the variability in signal penetration by analysing the seasonal evolution of derived surface elevations in respect to climate parameters. The main study targets are Austfonna ice cap on Svalbard and three ice rises in Dronning Maud Land, East Antarctica, where extensive ground-truth data are available. We find that the results of POCA and swath processing complement each other very well: POCA locations concentrate along ice divides whereas the swaths give good coverage in gentle slopes which are not resolved by POCA. A combined approach has the potential to improve current DEMs in coastal Antarctica and increase the coverage of elevation-change measurements at the margins of ice sheets and glaciers where most of current mass losses take place.


5:10pm - 5:30pm

Swath Processing of CryoSat-2 for the Study of Ice Caps and Mountain Glaciers

Noel Gourmelen1, Paul Tepes1, Albert Garcia2, Maria Jose Escorihuela2, Jan Wuite3, Luca Foresta1, Thomas Nagler3, Monica Roca2, Andrew Shepherd4, David Brockley5, Steven Baker5

1University of Edinburgh, United Kingdom; 2isardSAT, Spain; 3ENVEO, Austria; 4Center for Polar Observation and Modeling, University of Leeds, UK; 5MSSL, University College London, UK

Satellite altimetry has been used extensively in the past few decades to observe changes affecting large and remote regions covered by land ice such as the Greenland and Antarctic ice sheets. Glaciers and ice caps have been studied less extensively due to limitation of altimetry over complex topography. However their role in current sea-level budgets is significant and is expected to continue over the next century and beyond (Gardner et al., 2011), particularly in the Arctic where mean annual surface temperatures have recently been increasing twice as fast as the global average (Screen and Simmonds, 2010).

Radar altimetry is well suited to monitor elevation changes over land ice due to its all-weather year-round capability of observing ice surfaces. Since 2010, the Synthetic Interferometric Radar Altimeter (SIRAL) on board the European Space Agency (ESA) radar altimetry CryoSat (CS) mission has been collecting ice elevation measurements over glaciers and ice caps. Its Synthetic Aperture Radar Interferometric (SARIn) processing feature reduces the size of the footprint along-track and locates the across-track origin of a surface reflector in the presence of a slope. This offers new perspectives for the measurement of regions marked by complex topography.

More recently, data from the CS-SARIn mode have been used to infer elevation beyond the point of closest approach (POCA) with a novel approach known as “swath processing” (Hawley et al., 2009; Gray et al., 2013; Foresta et al., 2016). Together with a denser ground track interspacing of the CS mission, the swath processing technique provides unprecedented spatial coverage and resolution for space borne altimetry, enabling the study of key processes that underlie current changes of ice caps and glaciers.

In the frame of the CryoSat+ Mountain Glacier project, we use CS swath observations to generate global maps of ice elevation change over ice caps and glaciers. Here we present results over most of the world’s ice caps and elected glaciers and discuss the benefit of swath processing for assessing glaciers and ice caps changes and their contribution to changes in sea level.


5:30pm - 5:50pm

Cryosat-2 Altimetry of BC Coastal Mountain Glaciers

Jim Gower1, Stephanie King2

1Institute of Ocean Sciences, North Saanich, BC, Canada; 2Sea This Consulting, Nanaimo, BC, Canada

Cryosat-2 altimetry for the period July 2010 to January 2016, shows wide-spread melting of glaciers in the southern part of the British Columbia (BC) Coastal Mountain range in western Canada. The SARIN altimeter on Cryosat-2 is in synthetic aperture mode in this area, recording elevations of suitably-sloping targets out to about 5km cross-track from nadir and hence giving full coverage between tracks separated by 5km. Average height change rates were computed for small, overlapping sub-regions covering the study area. Sub-regions at altitudes less than 1500m showed rates clustered symmetrically about zero. These targets could be confirmed by visual inspection to be from rock, soil or vegetated targets. Above 2000m more than half the targets show a broader distribution, indicating reducing altitudes (melting) by up to 2m.year-1. This second distribution is from the surface of glaciers. Melt rates above 1500m decrease with increasing altitude and are lower before the start of 2013 than in the three years afterwards. Absence of negative melt rates (i.e. growing glacier heights over the full study period) is especially striking. Results show the capability of Cryosat-2 to measure individual and average melt rates on a time scale of 2-3 years.



 
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