## 3 Results  
### DEM Construction  
The filtered interferogram after the flat Earth phase removal is shown in Figure 3a. Given the very short temporal baseline of only 10 s, very high coherent interferometric phases were maintained over nearly the entire scene, even on sea ice near the glacier terminus (i.e., the upper part of the interferogram). Very short wavelength of the fringes caused by the high sensitivity of the height ambiguity could be found in the bedrock region near the glacier margin, whereas a low fringe rate was shown on the glacier surface. Very detailed topographic characteristics of the glacier surface were retrieved by the high sensitivity of the height ambiguity. Although phase unwrapping of the longer wavelength fringes on the relatively flat slope area was not a significant issue, the differential interferogram subtracted from the simulated topographic phase of the GIMP DEM was calculated (Figure 3b). Note that a relatively high rate of fringe was sufficiently eliminated overall in the areas. It was interesting that the GIMP DEM could be successfully utilized for subtraction topographic phases, even on rapidly moving surfaces. The coherence of the interferogram on the glacier surface was estimated as shown in Figure 3c. The coherence was well-maintained overall in areas, owing to approximately 10 s of short temporal baseline, except for the bedrock areas near the glacier terminus. It was quite interesting that very low  
Figure 2: Flowchart to construct digital elevation models (DEMs) using SAR observations. coherence was found over these areas, although we expected little surface change over approximately 10 s. The coherence map of the moving glacier surface, which we were interested in, presents a very high level of coherence. The mean coherence was 0.84 \(\pm\) 0.19 for the glacier surface, and 0.75 \(\pm\) 0.25 for the entire region. Notably, there was a relatively lower coherence on the glacier surface (the red circle in Figure 3c), and we suspected that the glacial surface which had a greater roughness than that of the other parts of the glacier might prohibit maintenance of the coherence of the incidence angle that we used. Alternatively, the glacier in this area flowed instantaneously more rapidly than other parts of the glacier surface, even the glacier terminus, resulting in a rapid surface change that did not maintain the coherence even over approximately 10 s of temporal baseline. Probably these areas might be covered by comparatively wetter conditions than other areas. In addition, it was impressive that the highly coherent interferometric phases in the sea-ice region were captured. The coherence map with very high spatial resolution shows locations of cracks and crevasses, which cannot be clearly discriminated in the amplitude image (Figure 1b). Figure 4a shows the constructed DEM scaled only from 0 to 450 m, excluding the bedrock areas which have a higher elevation, as we are interested in the topography of the glacier surface. The topographic height of the minor tributaries, as well as the primary tributary of the Petermann Glacier, were successfully retrieved using the pursuit monostatic TanDEM-X pair with a large perpendicular baseline configuration. To impose the usefulness of the large perpendicular baseline in a low slope area, we also show the constructed DEM scaled from 15 to 100 m in Figure 4b. The global TanDEM-X DEM and the GIMP DEM are shown in Figure 4c,d, respectively, for visual inspection at the same scale. First, the constructed DEM showed the most detailed topographic variation over the glacier surface compared to that of other two DEMs. The 12 m of high spatial resolution of the global DEM also showed the detailed topographic surface of the glacier. However, the relatively more moderate to larger height of ambiguity ranges from 30 to 45 m provided less detailed topographic features compared to those of the derived DEM using the TanDEM-X Science Phase observation.