Abstract
A digital representation of ice surface velocity is essential for a variety of glaciological, geologic and geophysical analyses and modeling. Here, we present a new, reference, comprehensive, high‐resolution, digital mosaic of ice motion in Greenland assembled from satellite radar interferometry data acquired during the International Polar Year 2008 to 2009 by the Envisat Advanced Synthetic‐Aperture Radar (ASAR), the Advanced Land Observation System (ALOS)'s Phase‐Array L‐band SAR (PALSAR) and the RADARSAT‐1 SAR that covers 99% of the ice sheet in area. The best mapping performance is obtained using ALOS PALSAR data due to higher levels of temporal coherence at the L‐band frequency; but C‐band frequency SAR data are less affected by the ionosphere. The ice motion map reveals various flow regimes, ranging from patterned enhanced flow into a few large glaciers in the cold, low precipitation areas of north Greenland; to diffuse, enhanced flow into numerous, narrow, fast‐moving glaciers in the warmer, high precipitation sectors of northwest and southeast Greenland. We find that the 100 fastest glaciers (v> 800 m/yr) drain 66% of the ice sheet in area, marine‐terminating glaciers drain 88% of Greenland, and basal‐sliding motion dominates internal deformation over more than 50% of the ice sheet. This view of ice sheet motion provides significant new constraints on ice flow modeling.
Highlights
[3] Here, we present a nearly complete velocity mosaic of the Greenland Ice Sheet assembled from satellite radar interferometry data acquired during the International Polar Year 2008–2009 by three instruments
[4] We use data collected by 3 sensors aboard satellite platforms managed by 3 space agencies: 1) the European Envisat Advanced Synthetic-Aperture Radar (ASAR), 2) the Japanese Advanced Land Observation System (ALOS)’s Phase-Array L-band SAR (PALSAR) and 3) the Canadian RADARSAT-1 SAR
C-band data provide high quality estimates in the north, but their long repeat cycle (35-day for ASAR and 24-day for RADARSAT-1) limits signal coherence and the derivation of ice velocity in the south. Exceptions to this rule are rare, e.g., Envisat ASAR in southwest Greenland in fall 2009 (Figure 1c)
Summary
[2] The Greenland Ice Sheet, with an area of 1.71 million km and an ice volume of 2.85 million km, contains enough ice to raise sea level by 7 meters and is principally drained by a set of a few hundred outlet glaciers [Weidick, 1995]. Ice velocity varies from a few cm per year near topographic divides to several km per year along fast-moving outlet glaciers. Knowledge of ice velocity is essential to identify areas of fast flow, estimate ice discharge into the ocean, study the temporal and spatial dynamics of ice deformation in relation to climate forcing, analyze the impact of flow rates on ice history, constrain numerical models of ice sheet evolution, and other purposes. [3] Here, we present a nearly complete velocity mosaic of the Greenland Ice Sheet assembled from satellite radar interferometry data acquired during the International Polar Year 2008–2009 by three instruments. We discuss how the map was assembled, the precision of the results, their limitations, the distribution of glacier velocity and the significance of the ice flow structure of the Greenland Ice Sheet revealed by this map
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