Ice Velocity Measurements From The First Sentinel-1a Full Antarctic Ice Sheet Campaign

Abstract:

We present an overview of ice velocity measurements produced from data acquired during the first Sentinel-1 full Antarctic ice sheet campaign. Satellite observations acquired over the past 25 years have shown marked ice velocity speed up on individual Antarctic ice streams, with ice velocity increases of over 42% observed on Pine Island Glacier. In Antarctica, areas of ice velocity speed up are dynamically unstable and comprise the largest component of ice sheet sea level rise contribution. However, despite a clear long term trend for increasing ice velocity in many regions, speed up has not been constant through time and multiple years with no significant change have also been observed. It is necessary to make present day measurements of ice velocity to provide an independent means of measuring ice mass loss from the most rapidly changing ice sheet regions. However the spatiotemporal coverage of historical ice velocity measurements has been limited by a paucity of suitable data over the full Antarctic ice sheet and to date, parts of east Antarctica have been observed only a few times during the last 25 years. We present 12 months of ice velocity measurements on 10 key Antarctic ice streams, produced from the normalised cross-correlation of real-valued intensity features in Interferometric Wide Swath (IW) mode Sentinel-1a data. A time series of ice velocity measurements produced from short 12-day repeat Sentinel-1a data over Pine Island Glacier shows that in 2014 and 2015 the ice surface speed has remained constant at ~4 km/year. A Sentinel-1a ice velocity map of the Antarctic Peninsula demonstrates that good quality measurements can be obtained along the full length of the Peninsula using Sentinel-1a. TOPS mode SAR Interferometry (InSAR) results shows that interferometric coherence can be preserved over the 12-day repeat period on stable slower flowing ice covered terrain, however on fast flowing ice streams such as Totten Glacier in East Antarctica and Pine Island Glacier in West Antarctica InSAR is less successful. We conclude that the short 12-day repeat period and large scale coverage of Sentinel-1a is an invaluable new resource, which in the future will be a critical tool for monitoring ice velocity change and dynamic instability of the Antarctic ice sheet.