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 
3. ASSESMENT OF THE INTERMEDIATE DEM 
3.1 Production Status 
The acquisition of the first global coverage was completed by 
January 2012. The following two months were used for 
additional acquisitions of difficult areas. By April 2012 a total 
of 135,000 RawDEMs have been prepared for calibration and 
mosaicking. The remaining first year acquisitions are scheduled 
to be processed by ITP and MCP Preparation until May 2012. 
On basis of the available data first calibration and mosaicking 
tests are currently conducted. The operational IDEM production 
is planned to start in summer 2012. 
By the end of March 2012 the acquisition of the second 
coverage started. It will take approximately one year followed 
by additional acquisitions where necessary. The final 
TanDEM-X product generation will start in 2013 and will be 
finished in 2014. 
3.2 Validation results 
Within the mosaicking the acquisitions are corrected by the 
estimated offset and tilts. The absolute accuracy of the resulting 
IDEM is checked against reference data like SRTM C-Band, 
ICESat data, high resolution DEMs or GPS tracks. Note that the 
differences are always calculated TanDEM-X - Reference data. 
In order to evaluate the relative height accuracy the absolute 
differences between neighboring acquisitions are computed. 
The requirement for the relative accuracy refers only to random 
errors (systematic errors are not considered). This means, that 
90% of all differences around the mean have to be below 2m in 
an area of 100km x 100km (linear 90% point-to-point error). 
3.2.1 Test Site Manitoba, Canada: The first test site 
consists of 8 acquisitions covering the north-western part of 
Minnesota, USA and the southern part of Manitoba, Canada. 
Figure 1 depicts the RawDEM outlines (red) and the resulting 
1°x1° DEM tiles (black). The terrain of the test site is 
moderately flat and sparely vegetated. The calculated offsets 
and tilts are below 2m and 8mm/km respectively. 
The Tile N49W98 - the name refers to the lower left corner - 
was investigated in more detail, as it contains a GPS track with 
a height accuracy of < 0.5m. The mean difference between 
TanDEM-X and the GPS heights is -0.56m with a standard 
deviation of 1.14m (Figure 2). The comparison to ICESat 
results in a mean difference of 0.19m with a standard deviation 
of 0.24m (Figure 3). Even for a DEM generated with only one 
coverage these results prove full compliance with the absolute 
height requirements (Table 1). Also, the difference to SRTM 
shows very good results with a mean below 2m. As TanDEM-X 
is more accurate, remaining SRTM errors (e.g. typical SRTM 
waves) are visible in the difference image (Figure 4). The 
relative height accuracy, estimated by calculating the absolute 
differences between neighboring acquisitions, is well below the 
required 2m (Figure 5). 
  
  
  
  
  
Reference Mean Std.dev | LE90 # points 
[m] [m] [m] 
GPS -0.56 1.14 1.75 4550 
ICESat 0.19 0.24 0.38 2021 
SRTM 1.80 1.49 2.30 all 
Neighbor 0.68 0.67 0.57 all 
  
  
  
  
  
  
  
Table 1: Differences of IDEM tile N49W98 to reference data 
(mean, standard deviation, linear 90% point-to-point error, 
number of points) 
46 
  
1°x1° tiles marked black, tile N49W98 marked green 
   
- ¥en 
M 
Figure 2: Difference between TanDEM-X and GPS o 
amplitude mosaick, North-Eastern part of tile N49W98 - area 
  
  
around Winnipeg, range of values [-3; 3] 
ABDRR-ICESA1 
   
  
  
   
Figure 3: Difference between TanDEM-X and ICESat on 
amplitude mosaick, tile N49W98, range of values [-5; 5]