GEOCODING OF TERRASAR-X DATA 
A. Roth, M. Huber, D. Kosmann 
DLR, German Remote Sensing Data Center, Oberpfaffenhofen, D-82234 Wessling, Germany - (Achim.Roth, 
Martin.Huber, Deltev.Kosmann)@dlr.de 
KEY WORDS: Geometry, Rectification, SAR, Orthoimage, System, Multiresolution, Multisensor, Multifrequency 
ABSTRACT: 
TerraSAR-X is a new German radar satellite that shall be launched in April 2006. The expected lifetime is 5 years. It carries a high 
frequency X-band SAR sensor that can be operated in different modes and polarisation. The Spotlight-, Stripmap- and ScanSAR- 
modes provide high resolution SAR images for detailed analysis as well as wide swath data whenever a larger coverage is required. 
Imaging will be possible in single, dual and quad-polarisation. TerraSAR-X will be an operational SAR-system for scientific and 
commercial applications. 
DLR currently develops the TerraSAR-X Ground Segment. One part is the geocoding system that will provide geocoding capability 
for multi-resolution, multi-polarisation and multi-frequency data. The user can select different products with respect to the geometric 
processing and quality. Multi-look ground range products as well as ellipsoid and terrain correction capabilities are provided. A new 
product called Enhanced Ellipsoid Corrected will be offered. It considers Digital Elevation Models (DEM) of a moderately coarser 
resolution than the 1 up to 3 m resolution of the TerraSAR-X modes. SRTM/X-SAR DEMSs with approximately 25 m spacing will be 
the backbone for this operational and fully automated service. The system design considers the processing of SAR data provided by 
other sensors as well. High precision terrain correction using high resolution DEMS, tie-pointing and image adjustment will be 
implemented in an experimental processor. 
1. INTRODUCTION The German Aerospace Center (DLR) currently implements the 
satellite control system and the payload ground segment for 
TerraSAR-X is a new German radar satellite that shall be receiving, processing, archiving and distribution of the X-band 
launched in April 2006. The scheduled lifetime is 5 years. It's SAR data. Part of the TerraSAR-X Ground Segment is the 
high frequency X-band SAR sensor can be operated in different geocoding system. In order to cover the different features of the 
modes and polarisation. The SpotLight- (1.3 m), StripMap- (3.3 TerraSAR-X sensor the system is parameterised with respect to 
m) and ScanSAR-modes (14.8 m) provide high resolution SAR the resolution and the number of layers (polarisation). 
images for detailed analysis as well as wide swath data The development is based on the experiences and techniques 
whenever a larger coverage is required. Imaging will be available from the ERS-1/2, SIR-C/X-SAR, SRTM and 
possible in single, dual and quad-polarisation. Beam steering Envisat-ASAR missions (Roth et al, 1996), (Rabus et al, 2003), 
enables observation in different incidence angles and double (Kosmann et al, 2000). New requirements rose due to the high 
side access can be realized by satellite roll maneuvers. The resolution capability of TerraSAR-X and a higher rate of 
satellite will be positioned in an 11 days repeat orbit. Figure | geocoded products as a global ortho-rectification service will be 
shows some details of TerraSAR-X satellite. The solar panel is offered. 
mounted on top of the satellite bus. The SAR antenna is visible The rectification procedure is based on the range-Doppler 
on the bottom side. The X-band downlink antenna is mounted approach developed by (Meier, 1989) and allows the geocoding 
on a small boom in order to avoid interference with the SAR- of other SAR data as well. SAR inherent distortions in 
antenna. ‘ combination with the multi-incidence and left- and right- 
" looking capability require the consideration of terrain 
information during the geocoding process. SRTM significantly 
improved the ortho-rectification service as it provides DEMs 
for almost 80% of the land surface. The corresponding terrain 
corrected product is called Enhanced Ellipsoid Corrected 
(EEC). The term “ellipsoid corrected” is used because it 
considers moderately coarser DEM resolution then the 1 to 3 m 
resolution of the TerraSAR-X modes. 
Complementary to the EEC high precision terrain correction 
can be performed using high resolution DEMs (e.g. from 
LIDAR), ground-control points and image adjustment 
techniques. As both resolutions of the DEM as well as the SAR 
image are in the same order of magnitude, this product is seen 
to be the equivalent to the Geocoded Terrain Corrected (GTC) 
product offered for ERS and SIR-C/X-SAR. A Geocoded 
domm Een layover shadow and Incidence angle Mask (GIM) can be 
Figure 1. Artist view on TerraSAR-X: generated as a by-product to GTC and EEC. 
    
     
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