## 3 Results
### Validation Using Existing DEMs  
To compare the topographic changes between the two collected DEMs and results of this study, two profiles along the A-A' and B-B' traverse lines shown in Figure 4a were drawn on Figure 5a,b. The red line was from the GIMP DEM, the blue line was from the TanDEM-X DEM in science phase observation, and the green line was from the global TanDEM-X DEM. It is certain that the constructed DEM in this study showed very detailed topographic variation along the two transect lines, particularly the B-B' transect line, in comparison to the other two DEMs. A similar topographic trend can be found in the profile of the A-A'. However, along the profile B-B', significant topographic variation could be detected by comparing the DEMs. The constructed TanDEM-X DEM showed very detailed topographic changes over the glacier surface, whereas the other two DEMs did not show very sensitive topographic information over the glacier. To investigate spatial details of each DEM, a frequency analysis using fast Fourier transform (FFT) was applied at each of the DEM profiles (Figure 5c,d). In the power spectrum of the profile A-A', similar or slightly higher frequency of derived TanDEM-X DEM was detected. Higher frequency component of the constructed DEM compared with the other DEMs was calculated in the profile B-B'. Thus, the TanDEM-X DEM with the small height of ambiguity reflected more detail topographic information, which can be useful for monitoring ice volume over a glacier. We also calculated a two-dimensional difference map between the constructed DEM and the other two DEMs to show that the constructed DEM had more detailed topographic surface information compared to that of the other two DEMs. As shown in Figure 6a,b, the constructed DEM shows very detailed topographic variation on the glacier surface. Thus, it is useful to understand and monitor glacial movement and flow characteristics. Given these DEMs were developed with different reference heights, it was difficult to calculate the precise estimation of the volume of ice loss using only these DEMs. However, the difference maps can be useful to determine which part and how much of the glacier surface has changed. Positive volume change of ice could be found at the glacier terminus in both of the difference maps. The negative volume changes could be detected along the margin of the glacier and some of its tributaries. Statistical analysis over the region of interest displayed in Figure 6  
Figure 5: Surface profiles along the (**a**) A-A’ and (**b**) B-B’ traverse lines shown in Figure 4a. The power spectrum (**c,d**) using frequency analysis on (**a**) A-A’ and (**b**) B-B’ was displayed. The red line is the profile of the GIMP DEM, the green line is from the global TanDEM-X DEM, and the blue line is based on the TanDEM-X Science Phase mode. The constructed TanDEM-X DEM shows very detailed surface characteristics, whereas the other two DEMs do not show much sensitive topographic variation along the B-B’ profile. was conducted and the results are presented in Table 3. They show a similar range of mean values; however, a lower standard deviation was found in the DEM constructed by this study. The scatter plots between the constructed TanDEM-X DEM and the two other DEMs are shown in Figure 7, for validation points using the software package Grapher (Golden Software). The validation points were chosen at the same position where the CryoSat-2 observations are available. We assumed that there was only an offset between the two heights as \(Y=X+\textit{offset}\). They showed a very good correlation of 0.998, and the offsets were calculated as \(-3.1\) m and \(-7.0\) m for the GIMP and Global DEM, respectively. Since the constructed DEM utilized the GIMP DEM as a reference height, a relatively smaller offset might have been estimated. Moreover, each DEM had a different height sensitivity level or vertical accuracy, which can be one of the reasons it was showing the offset difference.