The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
137 
portion of the comer reflectors. The reflection from the comer 
reflector is much stronger than neighbourhood. 
Figure 2 shows the comer reflector (CR) used in this study. The 
reflector consists of 3 sides of rectangular aluminium panels 
with 50 cm length. The panels are attached perpendicular to 
each other by bolts. We measured the coordinates of the CRs. 
using GPS (accuracy is better than several centimeters). From 
the comparison of the coordinates derived from TerraSAR-X 
and CRs, pixel location accuracy of TerraSAR-X was evaluated. 
Tokyo1 
Tokyo2 
Tsukuba 
Acquisition 
Date 
16 th Feb. 
2008 
29 th Nov. 
2007 
23 th Oct. 
2007 
Mode 
HS 
HS 
HS 
Incidence Angle 
39.4 
42.2 
52.7 
Orbit 
Ascending 
Descending 
Descending 
Scene Center 
35.7 N, 
139.8 E 
35.6 N, 
139.8 E 
36.1 N, 
140.1 E 
Table 5. Specification of used TerraSAR-X data. 
Figure 1. TerraSAR-X EEC product of Tokyo on 29 th Nov., 
2007 and an enhanced portion of the comer reflectors. 
3.2.1 Pixel location accuracy using science orbit: Table 6 
shows the comparison of location accuracy of both SSC and 
EEC product when science orbit information was used. This 
analysis was done using the image of Tokyo of 29 th Nov. The 
latest supplied processing system was applied to generate the 
level 1B product. 
The radar signal is subject to path delay due to the different 
refractive indices of vacuum, ionosphere and troposphere. This 
results in slant range error of the order of 2-3 m that depends on 
the actual conditions in the passed media and on the length of 
the signal path hence the incidence angle. This value is 
annotated in the meta data annotation file. 
The pixel location accuracy of the SSC product for slant range 
and azimuth was estimated using the projected spacing value 
for slant range and azimuth, respectively. Errors of slant range 
are 0.4 m, and azimuth is -0.5 m. Therefore the result of the 
pixel location accuracy is better than 1 m. Almost the same 
results were obtained for Tsukuba site. 
The pixel location accuracy for the northing (Y) direction was 1 
m, though easting (X) direction of the EEC product was not 
better than 1 m,. It is assumed that the vertical errors of DEM 
affect the pixel location accuracy of the EEC product. 
(a) SSC 
TSX 
GPS 
Difference 
Slant Range (pixel) 
2781.46 
2781.03 
0.43 
Azimuth (pixel) 
2727.04 
2727.62 
-0.58 
(b) EEC 
TSX 
GPS 
Difference 
X (m) 
392133.5 
392137.1 
-3.6 m 
Y (m) 
3948968.6 
3948967.6 
1.0m 
Table 6. The location accuracy of the SSC and EEC product 
calculated using the image of 29 th Nov. 
3.2.2 Pixel location accuracy comparison using another 
orbit type:Table 7 shows the comparison of location accuracy 
of EEC product by different orbit type. Even if smaller X 
deviations for the predicted orbit observed, that doesn’t mean it 
is more accurate because the errors of Y is much greater. 
It reveals that in this case the pixel location accuracy is almost 
same when using rapid and science orbit. This demonstrates 
that JPL real-time GPS products used for the generation of the 
rapid orbit product already provides high accuracies (Yoon et 
al., submitted). 
Predicted 
Rapid 
Science 
X (m) 
0.3 
-3.6 
-3.6 
Y(m) 
11.7 
1.0 
1.0 
Table 7. Comparison of the location accuracy of the EEC 
product by different orbit types. The acquisition 
date is 29 th Nov. 
Figure 2. Comer reflector used in this study.