The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
204 
2.1 Study site 
The study site was selected in the periphery of Lake 
Imja which is known as one of the most dangerous 
glacial lakes in the world due to its rapid expansion and 
huge amount of water storage capacity (Figure 1). 
The majority of the supraglacial lakes that was formed 
in the 1960s recently became moraine-dammed lakes 
because of the glacier retreat. An example of those 
lakes is Lake Imja and has been identified as a potential 
threat to the Himalayans region. The lake was formed 
within moraines and rapidly stretching towards the 
glacier snout. The end moraine in Lake Imja measures 
600m wide and has a massive dead ice core which is 
frequently exposed. Rapid melting of the debris-covered 
ice and significant changes in this outlet position has 
been reported (Watanabe et al., 1994 and 1995). 
Figure 1. Lake Imja study site, ALOS/AVNIR-2 image, 
22 Oct 08. 
2.2 Utilized Data 
The study was carried out utilizing a pair TerraSAR-X 
images (Table 1, Figure 2 & 3). The interval to obtain 
the pairs of images was set at 11 days (the shortest 
inverval of satellite revisit) to achieve good quality of 
DEMs. Two different images were acquired at HS and 
SM for comparing different spatial resolutions. SRTM 
90m DEM data was utilized as reference DEM in this 
study which was generated through C-band single-pass 
interferometry. The accuracy of this DEM is about 
16m (vertical) (E. Rodriguez et al). 
Mode 
Date 
Direction 
Incident 
angle 
Polarization 
SM 
2008/3/24 
ascending 
35.36 
VV 
SM 
2008/4/4 
ascending 
35.36 
W 
HS 
2008/3/18 
decending 
39.39 
VV 
HS 
2008/3/29 
decending 
39.39 
VV 
Table 1 TerraSAR-X data acquisition dates. 
Figure 3. Lake Imja, TerraSAR-X image, SM, 04 Apr 08. 
2.3 InSAR processing 
The technique of SAR interferometry is widely 
practiced to produce the map of the topography or 
ground deformation. InSAR for the space-borne SAR is 
conducted by repeat-pass interferogram. In the repeat- 
pass mode, the orbit accuracy depends on the quality of 
DEMs. The orbit of TerraSAR-X is in a ±250 m tube 
with respect to a reference orbit (Eineder et al, 2003) 
and the orbit distance is shorter and hence a good DEM 
quality is expected. InSAR processing was conducted 
by SARscape® software in this study 
(http://www. sarmap. ch/). 
3. RESULS AND DISCUSSIONS 
We conducted the qualitative accuracy of the DEMs 
generated by the TerraSAR-X images and compared 
them with the SRTM data (Figure 4, 6 and 8). Coherent 
images shown in Figures 5 and 7, indicated the 
influence on the quality of the DEMs (SARScape®, 
Help Menu).