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approach to the use of space-borne datasets in time-critical 
situations. 
The spacecraft TerraSAR-X delivers unique, novel quality 
SAR satellite image data with a resolution of up to one metre, 
which can significantly augment the capabilities of armed 
forces, homeland security, and intelligence agencies, creating 
both tactical and strategic advantages. Reduced image speckle 
through multilooking and the presence of radar shadows of 
man made objects are important features of the high 
resolution TerraSAR-X images which will by far enhance the 
image interpretability over that of medium resolution SAR 
systems. 
Besides of updated high resolution imagery of the Earth’s 
surface, the availability of precise information on terrain 
evaluation is strongly requested by users of geo-spatial data. 
Currently most areas in the world are covered by an elevation 
grid of poor quality in terms of point density and height 
accuracy (ERS-1/2 Tandem, SIR-C/X-SAR, SRTM, 
GTOPO30). In order to close this gap of information towards 
the third dimension TanDEM-X (TerraSAR-X add-on for 
Digital Elevation Measurements) is a German program for a 
new generation SAR satellite operating at X-band in single 
pass SAR interferometry. The single pass SAR 
interferometric constellation, comparable to stereoscopic 
survey missions, is realized by two independent X-band 
satellites, TerraSAR-X together with TanDEM-X, flying in a 
close formation, quite often less than 1 km. The mission goal 
is to deliver a global digital elevation model characterized by 
a height accuracy of better than 2 m. The additional spacecraft 
TanDEM-X is already financed through a PPP agreement 
between DLR and EADS Astrium and will be launched in 
2009. 
The increasing demand of sophisticated geospatial data sets 
requires appropriate and precise planning documents in all the 
three dimensions. However, a continuous and up-to-date 
acquisition by optical sensors or airborne platforms is strongly 
limited either by unfavourable weather conditions or 
inefficient mission scenarios. Therefore, the easy access to the 
high-resolution radar missions TerraSAR-X and TanDEM-X 
gives the global remote sensing community the possibility to 
participate in one of the most ambitious space programs. 
3. THE SYSTEM 
TerraSAR-X will deliver high resolution SAR images with a 
ground sampling distance up to lm, in combination with 
unique satellite agility: The electronically steered antenna 
allows acquiring physically separated areas of interest within 
seconds without rolling the whole satellite. The satellite is 
mainly described by: • 
• TerraSAR-X is operated at X-band at 9.65 GHz. 
Even pure visual interpretation will profit from the 
fact that the short wavelength shows more spatial 
detail than longer wavelengths. 
• The chirp bandwidth, an indicator of the spatial 
accuracy level, is with 300 MHz the best 
performance currently in space. 
• Single, dual and quadruple polarizations allow for 
a more complex description of the areas and objects 
on the ground. Their availability depends on the 
imaging mode and always is a trade-off with the 
spatial coverage and swath width. 
• Radiometrically calibrated data allow for an easy 
comparison between scenes. 
• TerraSAR-X is both, daylight and weather 
independent, i.e. the system can record data at 
night and through clouds or dense smoke cover. 
• The system features a quick site access time of 2.5 
days to any point on Earth at 95% probability. 
• TerraSAR-X features a unique agility: it is possible 
to switch between its three different imaging modes 
and various polarisations within only 1 to 3 seconds, 
corresponding to surface acquisition offsets of only 
7 to 20 kilometres. 
• Time-critical data can be downloaded within 
seconds after acquisition to mobile ground stations 
on-scene, thus enabling near-real time data 
processing. 
• Anonymous and encrypted processes guarantee an 
unobjectionable confidentiality. 
• Furthermore, the satellite's very high resolution of 
up to 1 m and its high radiometric accuracy, make 
TerraSAR-X an ideal sensor to support sensitive 
decision-making in time-critical situations. 
• Satellite Tasking twice a day and priority settings 
for the ordered data takes allow for quick 
turnaround times in data delivery and late order 
changes. 
TanDEM-X will be an almost identically constructed system 
with some slight modifications for the necessary 
synchronization link between both satellites. 
4. IMAGE MODES AND PRODUCTS 
In the standard operating mode (so-called single receive 
antenna) image data in three different imaging modes can be 
acquired: SpotLight, StripMap and ScanSAR: 
• SpotLight with up to 1 m resolution (10 km 
(width) X 5 km (length) image size) - the most 
sophisticated radar imagery available on the market: 
In flight direction, the radar beam can be steered 
like a veritable spotlight, illuminating a particular 
ground scene for the longest time period possible, 
thus achieving a 1 metre class resolution as well. 
• StripMap with up to 3 m resolution (30 km X 
50 km standard scene size, extendable up to 
4,200 km acquisition length) - the ground swath is 
illuminated with continuous sequence of pulses 
while the antenna beam is fixed in elevation and 
azimuth. 3 
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