## 4 Practical Experiments
### Shisper Glacier
#### 4.1.2 Evaluation--Shisper Glacier
Notably, along the Muchowar glacier tongue, systematic ray intersection errors are observed, likely due to glacier movement during the 11-day image acquisition period, causing point displacement and triangulation inaccuracies. The 2019 DoD analysis of the PSS DEM in Ali Abad/Karimabad region (see Figure 9) shows a mean deviation of \(-0.02\) m (median deviation of \(0.03\) m), a StdDev of \(5.26\) m, and an NMAD of \(4.54\) m. Ref. [16] reported a mean deviation of \(-4.1\) m, a StdDev of \(13.6\) m, and an NMAD of \(12.3\) m using a DEM derived from WorldView-II and GeoEye-1 satellite images. While our results may appear better based on the numbers, it is important to note that [16] used a reference DEM of higher quality compared to the GLO-30 DEM. Therefore, such comparisons should be made cautiously, assuming, as with the PSS DEM from 2017, equivalent outcomes. Figure 7: Evaluation of the generated PSS DEM (2017) in the Ali Abad/Karimabad region, accounting for the steep terrain north of the village. From left to right: patches of the generated orthomosaic, the resulting DEM, DoD calculated with GLO-30 DEM, an error map highlighting mean intersection errors during triangulation, and an overview of the number of pairwise DEMs contributing to the final mosaicked DEM. Analyzing the patch in the steep terrain north of Ali Abad/Karimabad (see Figure 10) revealed findings consistent with the 2017 dataset. However, in the southern region, no systematic intersection errors were observed. Larger intersection errors along the steep slopes of the Hunza River are likely attributable to a combination of low texture, steep incidence angles, actual terrain changes, or inaccuracies in the reference DEM, which remain uncertain. Figure 8: The evaluation of the 2017 PSS DEM near the terminus of the Muchowar glacier encompasses the adjacent mountainous and partially snow-covered terrain. From left to right: patches of the generated orthomosaic, the resulting DEM, DoD calculated with GLO-30 DEM, an error map highlighting mean intersection errors during triangulation, and an overview of the number of pairwise DEMs contributing to the final mosaicked DEM. Figure 9: PSS DEM from 2019 over the stable area of Ali Abad village. The DoD illustrates the elevation differences between the PSS-derived DEM and the GLO-30 DEM. The accompanying histogram represents the DoD’s raster statistics, including mean, median, and StdDev. Additionally, the NMAD was computed for the outlined area, resulting in 4.54 m.  
The analysis of the Muchowar glacier patch in Figure 11 also reveals patterns similar to those observed in 2017. Two notable aspects emerge from the error map. First, the glacier appears to have undergone significant movement during the 12-day image acquisition period, explaining the pronounced intersection errors along the glacier tongue. Systematic differences are also evident in the DoD, aligning with the intersection errors observed here. The error map also highlights systematically higher errors in the northern region. Examination of the _Count_ map indicates a boundary between the image pairs used, suggesting that the configuration of these pairs may have been suboptimal, similar to the southern area of Ali Abad/Karimabad in 2017. Interestingly, these elevated errors are not as clearly reflected in the DoD, possibly because they remain below some kind of \"Level of Detection\" compared to the accuracy and GSD of the GLO-30 DEM. The DoDs for both timestamps show mostly random errors, with larger deviations in steep shadowed areas affecting stereo reconstruction. This suggests generally accurate DEMs with some localized discrepancies due to terrain or environmental factors. A comparison in steep areas with reference data of higher accuracy than the GLO-30 DEM would be interesting for future work. Figure 11: The evaluation of the 2019 PSS DEM near the terminus of the Muchowar glacier encompasses the adjacent mountainous and partially snow-covered terrain.