## 4 Results
### Comparison with Ice Motion from TerraSAR-X and PALSAR Data
For three ofthe glaciers, the S1 analysis provides velocities all along the terminus. For Jakobshavn Isbrae S1 and PALSAR are not able to track the motion down to the front because of the sharp velocity gradients across the ice stream. The S1 and TerraSAR-X velocity profiles shown in Figure 6 are separated in time up to one month. On Umiammaku Isbrae, Semreq Silarleq and Store Gletsjer the S1 and TerraSAR-X velocity profiles show close agreement, indicating, on the one hand, comparatively stable velocities during December 2014 and January 2015, and, on the other hand, similar performance of the two sensors for tracking velocities along the central flowlines. Regarding long-term trends, Semreq Silarleq and Jakobshavn Isbrae show significant acceleration. For Jakobshavn Isbrae, this trend is well documented, as well as the strong seasonal variations of velocity [30,32]. Figure 2: Maps of ice velocity on outlet glaciers of the Greenland west coast, derived from SAR data of **(a)** Sentinel-1, 3–15 January 2015; **(b)** TerraSAR-X, 11 days repeat pass from different epochs in December 2014 and February 2015; and **(c)** PALSAR, 20 November 2009–5 January 2010. DB–northern Disco Bugt; JI–Jakobshavn Isbrae. White lines show profiles of Figure 6: 1-Umiammaku Isbrae, 2-Sermeq Silarleq, 3-Store Gletsjer, 4-Jakobshavn Isbrae. Figure 4: Maps of ice velocity on outlet glaciers to the northern Disko Bugt (DB in Figure 2) derived from **(a)** SAR data of Sentinel-1, 3 to 15 January 2015. **(b)** TerraSAR-X, 9 to 20 December 2014. Dotted line: Coastline. Figure 3: SAR amplitude image of the glaciers Sermeq Kujallelq and Kangilernata Sermia, draining into the northern Disko Bugt, geocoded using the GIMP DEM at 30 m grid. **(a)** Section of Sentinel-1 IW image, 3 January 2015. **(b)** Section of TerraSAR-X image, 20 December 2014. Dotted line: Coastline on 20 December 2014. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Glacier**} & \multicolumn{2}{c}{**Front**} & \multirow{2}{*}{**Time Span S1**} & \multirow{2}{*}{**Time Span TerraSAR-X**} & \multirow{2}{*}{**Time Span PALSAR**} \\  & **Coordinates** & & & \\ \hline Umiammakku & 71.727\({}^{\circ}\)N & 22. December 2014– & 12 December 2014– & 15 September–31 October 2008 \\ Isbrae & 52.397\({}^{\circ}\)W & 3 January 2015 & 1 January 2015 & 20 November 2009–5 January 2010 \\ \hline \multirow{4}{*}{Sermeq} & \multirow{4}{*}{70.830\({}^{\circ}\)N} & \multirow{2}{*}{22 December 2014–} & \multirow{2}{*}{16–27 December 2014} & \multirow{2}{*}{15 September–31 October 2008} \\  & & 3 January 2015 & & 20 November 2009–5 January 2010 \\ \cline{1-1}  & & 3–15 January 2015 & & \\ \hline \multirow{3}{*}{Store Gletsjer} & \multicolumn{2}{c}{70.378\({}^{\circ}\)N} & \multirow{3}{*}{3–15 January 2015} & \multirow{3}{*}{3–14 February 2015} & \multirow{3}{*}{15 September–31 October 2008} \\  & 50.611\({}^{\circ}\)W & & & 20 November 2009–5 January 2010 \\ \hline Jakboshavn & 69.147\({}^{\circ}\)N & \multirow{3}{*}{3–15 January 2015} & \multirow{3}{*}{8–19 February 2015} & \multirow{3}{*}{15 September–31 October 2008} \\  & 49.571\({}^{\circ}\)W & & & 20 November 2009–5 January 2010 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Specifications for ice motion analysis along central flowlines of outlet glaciers in Greenland west coast (shown in Figure 6). Location of velocity profiles in Figure 2. Coordinates specified for center point of calving fronts in January 2015. Time span refers to epoch for velocity retrievals. Figure 5: Maps of ice velocity on Jakobshavn Isbrae (JI in Figure 2) derived from (**a**) SAR data of Sentinel-1, 3 to 15 January 2015. (**b**) TerraSAR-X, 8 to 19 February 2015. Dotted line: Coastline. Grey area: no velocity data obtained from S1. Figure 6: Maps of ice velocity along central flowlines for Umiammakku Isbrae, Sermeq Silarleq, Store Gletsjer, and Jakobshavn Isbrae. Distance upstream of ice front in January 2015. Location of profiles in Figure 2.