polarstereo, latitude longitude. When GCP exists, we can 
make the absolute DEM. 
By using quality flags, DEM is able to be interpolated from 
neighbor data, converted into a fixed value. 
DEM provided by observation of multiple times is possible 
to be upgraded to high accuracy data. Also DEM mosicing 
is available. 
5. ESTIMATION OF ACCURACY 
5.1 DEM accuracy using ASTER simulation 
When there is no error at orientation elements and stereo 
matching, the precision of DEM is decided by B/H and 
ground resolution. 
As ASTER data weren’t available yet, we made ASTER 
simulation data made from JERS-1 OPS data. 
ASTER data is stereoscopic on the along track direction 
same as JERS1data. 
We estimated the accuracy of ASTER DEM data through 
ASTER simulation data were processed. 
The condition of process is follows. 
(1) Original DEMis used to elevation data to be generated 
from 1:25000 topographic map by Geographical Survey 
Institute of Japan. 
(2)Image data is resampled from JERS1 data. 
(3)Orientation image data is calculated from JERS1 data. 
(4)ASTER backword image data is calculated from original 
DEM and orientaion image data. 
The result of estimation shows table 2. Also figure 3 
shows generated ASTER simulation data and figure 4 
shows original DEM and generated DEM. 
Figure 5 shows the result of extraction of water area as 
impossible matching area. 
Table 2 Accuracy of Elevation 
  
  
  
  
Positive | Negative | Average |R.E.M. 
Maximum | Maximum | Error (m) | S(m) 
Error (m) | Error (m) 
175 -199 0.87 12.31 
  
  
  
  
  
As this case has no error in orientation data, the cause of 
error seems to be mismatching. 
The orientation elements are decided by system 
configuration. The position knowledge of EOS-AM1 
spacecraft becomes high to utilize data of TONES 
satellite compared with others spacecraft. Therefore 
orientation error isn't mainly cause in elevation error. 
And, It is easy to be matching on stereoscopic image in 
along track direction, compared with one on cross track 
direction. Therefore, the accuracy of DEM using real 
ASTER data will be not change one of simulation data. 
876 
5.2 The caurse of Mismatching 
The area where mismatching are occurred are estimated 
that JERS-1 data were processed about 30 scenes 
include desert zone, tropical rain forest zone, a grassy 
plain, steep mountain zone. As a result, the area where 
mismatching are occurred had the next characteristic. 
(1) when the same intensity level 
(2) when resemblance pattern continues 
(3) when saturation data exist 
(4) when area of the sea, cloud level exists 
(5) shadow department of clouds 
JERS-1 data has the capability that are B/H=0.3, ground 
resolution=18m and 24m. In case of JERS1 data, the 
accuracy of DEM is settled 60m-80m. It's average is 
estimated with 30m-40m. 
The results of experiment were able to get several 
characters near by a theory value, showed in the table. 
On the other hand, ASTER data has the capability that are 
B/H=0.6, the ground resolution=15 m. In case of ASTER 
data, the accuracy of DEM is settled 12.31m. It’s near a 
theory value. 
6. FUTURE 
ASTER DEM product's accuracy will be 12.5m that has 
the potentiality of drawing 1:100,000 scale topographic 
map. 
The Algorithm will be upgrading, especially searching 
method of stereo tie point, extraction method of 
mismatching area. 
7. REFERNCE 
(1)ERSDAC, 1995. Algorithm Theoretical Basis Document 
for ASTER Level-1 Data Processing. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996