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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
    
Figure 1 1: Subset tile N34W78, amplitude mosaick 
For the water indication mask the amplitude and the coherence 
are evaluated as mentioned above. Figure 14 shows a 
visualisation of the WAM. The beige colored pixels indicate 
water derived solely from the amplitude, light blue indicates 
water found in the amplitude and the coherence. Dark blue 
indicates water found in the amplitude and the coherence of two 
overlapping acquisitions. 
Near the scene center, where two bridges cross the river, it can 
be seen that the amplitude and coherence flag complement one 
another very well. Although, the coherence does not indicate 
water here it is found by the amplitude threshold. 
Smaller lakes, like e.g. the two which can be seen in the middle 
left of the amplitude image, fall below the minimum mapping 
unit for lakes and rivers which is two hectares (20,000 m?). 
In a later editing step it is planned to use the water indication 
mask for flattening noisy DEM areas over water. A first study 
for this DEM editing step and more detailed information about 
WAM generation can be found in (Wendleder et al. 2012). 
5. CONCLUSIONS 
First calibrated and mosaicked intermediate TanDEM-X DEMs 
were presented. In flat and sparsely vegetated areas the 
validation shows an absolute height accuracy of better than 2m 
with respect to all reference data. 
Also in hilly and vegetated areas the height criteria can be met 
already with the first coverage. The difference to USGS 
Seamless data with about 10m is explainable as this dataset is a 
terrain model, while the TanDEM-X DEM is a surface model. 
On the other hand the comparison to SRTM and ICESat show 
good absolute accuracy of better than 7m. 
More mountainous test sites were not considered up to now, as 
there may be phase unwrapping errors. These errors need at 
least an additional acquisition and dual baseline processing to 
be resolved for DEM generation. 
    
    
Mg 
Figure 12: Subset tile N34W78, color shaded DEM 
Figure 13: Subset tile N34W78, height error map 
  
Figure 14: Subset tile N34W78, water indication mask, beige: 
water derived from amplitude, light blue: water derived from 
amplitude and coherence, dark blue: water derived from 
amplitude and coherence in two acquisitions 
49