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EVALUATION OF THE GEOMETRIC ACCURACY OF TERRASAR-X 
T. Nonaka *, Y. Ishizuka, N. Yamane, T. Shibayama, S. Takagishi, T. Sasagawa 
PASCO Corporation, 2-8-10 Higashiyama, Meguro-ku, Tokyo, Japan 
takashi_nonaka@pasco .co.jp 
KEY WORDS: validation, geometric accuracy, synthetic aperture radar, basic product 
ABSTRACT: 
The TerraSAR-X launched on June 15, 2007 is one of the most state of the art satellite sensors. Its sophisticated feature is in demand 
for the application for map generation and monitoring purposes. One of the basic products of TerraSAR-X is the Enhanced Ellipsoid 
Corrected (EEC) orthorectified image. The product is projected to map geometry and terrain induced distortions are corrected using 
a digital elevation model (DEM). The geometric accuracy of this product depends on the referred DEM. In this study, we evaluated 
the pixel location accuracy of the product by two methods. The method using comer reflectors shows that the pixel location 
accuracy of SSC product was better than 1 meter, and that of EEC product was better than 5 meter in the flat area. On the contrast, 
the pixel location accuracy of the mountain areas evaluated by comparison with digital maps was reduced. It reveals that the 
enhancement of the orthorectified product is necessary for considering the creation of the topographic maps using TerraSAR-X data. 
1. INTRODUCTION 
TerraSAR-X is the latest German radar satellite that has been 
launched on June 15, 2007. The objective of the mission was to 
develop an operational spacebome X-band synthetic aperture 
radar (SAR) system in order to produce various products for 
commercial and scientific use (Weminghaus et al., 2004). 
The applications of TerraSAR-X include environment planning, 
land cover mapping, natural resource exploration, regional and 
urban development, crisis response, security intelligence and so 
on (Schmidt and Janoth, 2007). Especially for the DEM, 
TanDEM-X will make it possible to generate the high-quality 
DEMs of any area on the globe (Krieger, et al., 2005). 
In order to evaluate the usefulness of TerraSAR-X data for the 
generation of topographic maps, the geometric accuracy of the 
SAR data should be analysed. The calibration and validation 
concept was planned before launching, and one of the subjects 
is geometric calibration (Schwerdt et al., 2005). In previous 
study, individual error budgets, such as orbit accuracy, DEM 
accuracy, atmospheric refraction, were calculated by the 
simulation (Frei et al., 2004). This simulation revealed that the 
geometric accuracy was mainly restricted by the quality of 
DEM. 
The present study evaluated the geometric accuracy of the EEC 
basic product of TerraSAR-X. Our existing processing system 
uses the SRTM DEM with 90 m spatial resolution for 
generating orthorectified products (EEC) because DEMs of 
better quality are not available on a global scale (Hiramatsu et 
al., 2008). The study site was mountain area as well as flat 
ground to evaluate the effects of used DEM. 
2. FEATURES OF TERRASAR-X 
2.1 Specifications and Features 
TerraSAR-X is a side-looking X-band synthetic aperture radar 
(SAR) based on active phased array antenna technology (Roth 
and Weminghaus, 2006). It is the first satellite to be built in a 
Public Private Partnership (PPP) in Germany: The German 
Aerospace Center (DLR) and Europe's leading satellite system 
specialist, EADS Astrium. DLR holds the rights for the 
scientific exploitation of the data, while Infoterra GmbH holds 
the exclusive rights for the commercial exploitation of the data 
product. 
The operational lifetime is 5 years. The TerraSAR-X satellite 
flies in a sun-synchronous dawn-dusk 11 days repeat orbit at an 
altitude of 514 km at the equator. Table 1 shows the 
specification of the satellite (German Aerospace Center). 
Repeat Cycle 
11 days 
Orbit per day 
15 2/11 
Local time at ascending 
node equator crossing 
18:00+/- 15 minutes 
Altitude at equator 
514.8 km 
Inclination angle 
97.44 ° 
Ground track repeatability 
+/- 500 m per cycle 
for mapping 
Table 1. TerraSAR-X key orbit parameters. 
The instrument timing and pointing of the electric antenna can 
be programmed allowing numerous combinations. From the 
many technical possibilities, four imaging modes have been 
designed to support a variety of applications ranging from 
medium resolution polarimetric imaging to high resolution 
mapping. The active beam steering of the SAR antenna allows 
for high resolution imagery. The following imaging modes are 
defined for the generation of basic products. 
-High resolution SpotLight Mode HS in single or dual 
polarization 
-SpotLight mode SL in single or dual polarization 
-StripMap mode SM in single or dual polarization 
-ScanSAR mode SC in single polarization 
* Corresponding author.