TerraSAR-X and TanDEM-X: 
Revolution in Spaceborne Radar 
Ralf Düring, Fifame N. Koudogbo, and Marco Weber, 
Infoterra GmbH, 88039 Friedrichshafen, Germany 
INTRODUCTION 
While Earth Observation from space in the past was mainly 
focused on scientific purposes, today data and the derived 
information products are increasingly used for various 
commercial applications. Potential users are planning and 
consulting offices, food and natural resource industries, 
insurance companies or agencies. New data of enhanced quality, 
available quickly and reliably, independently of daylight and 
weather conditions, are required for an increasing and sustained 
commercial exploitation of Earth Observation data. 
The design and performance of TerraSAR-X, high resolution 
satellite X-band satellite, built on a public-private-partnership 
agreement between the German Aerospace Centre DLR and 
EADS Astrium GmbH will exactly meet these requirements. 
Launched on the 15 th June 2007 from the Russian Cosmodrome 
in Baikonur (Kazakhstan), the Synthetic Aperture Radar (SAR) 
instruments of the spacecraft supply radar images of high quality, 
day and night and under nearly all weather conditions; leaving 
thus the way open for the establishment of a worldwide 
commercial EO-market and the development of numerous 
applications, products and services. 
Those services include highly sophisticated client-specific image 
interpretation, topographic maps up to a scale of 1:10,000, geo 
spatial databases and terrain analysis in demand for a wide scope 
of applications. Other purposes comprise environmental 
planning, land cover and natural resource exploration, regional 
and urban development, insurance, risk assessment and 
humanitarian objectives, particularly in time-critical situations, 
as well as applications in border control, security and defence. 
Moreover the smallest movements of the Earth's surface due to 
tectonics, volcanism, earthquakes, and land slides are further 
challenging fields of application of TerraSAR-X interferometry. 
1. TERRASAR-X BASIC IMAGE PRODUCTS 
The TerraSAR-X is a Synthetic Aperture Radar instrument 
based on an active phased array technology. The radar carrier 
frequency is of 9.65GHz (X-band). The nominal range 
bandwidth is 150 MHz, the maximum one 300 MHz. The 
spacecraft was successfully launched into a sun-synchronous 
dusk-dawn orbit with a nominal orbit height at the equator of 
514 km. It is flying at a velocity of about 7,6km/s; this results in 
about 15 revolutions around the Earth per day and in a revisit 
time of 11 days. Fehler! Verweisequelle konnte nicht 
gefunden warden, presents an overview of the TerraSAR-X 
main orbit parameters. 
Parameter 
Mission Orbit 
_ Qrbit type 
Sun-synchronous repeat orbit 
Repeat Period 
11 days 
Repeat cycle 
167 orbits in the repeat 
Orbits per day 
15% 
Equatorial crossing 
time 
18:00 ± 0.25h (local time) 
Inclination 
97.4438° 
Altitude at equator 
514.8 km 
TerraSAR-X Orbit parameters 
1.1 TerraSAR-X imaging Modes 
TerraSAR-X sensor is designed for multiple imaging modes and 
can acquire in StripMap, SpotLight and ScanSAR modes with 
single-, dual- or full polarization. The characteristics of each 
imaging mode are described in the following subsections. 
1.1.1 The StripMap mode 
The ground swath is illuminated with continuous sequence of 
pulses while the antenna beam is fixed in elevation and azimuth 
(Fig. 1). This results in an image strip with a continuous image 
quality in the flight direction. Besides dual polarization 
StripMap images will even be available as quadruple 
polarisation data that are still under investigation. 
Satellite Orbit 
Fig. 1: The StripMap imaging geometry 
Single pol SM 
Dual pol SM 
Polarizations 
HH or VV 
HH/VV, HH/HV 
or VV/VH 
Scene dimensions 
50km x 30km 
50km x 15km 
Full performance 
range 
20° - 45° 
20° - 45° 
Azimuth 
resolution 
3.3m 
6.6m 
Ground range 
resolution 
1.70-3.49m 
(@45°...20°inc) 
1.70-3.49m 
(@45°...20°inc) 
The SpotLight (SL) and High Resolution SpotLight (HS) modes 
Two variants of the spotlight mode (Spotlight (SL) and High 
Resolution SpotLight (HS)) are designed with different values 
for azimuth resolution and scene size. As depicted in Fig. 2, SL 
and HS modes use electrical beam steering in azimuth direction 
in order to increase the illumination time, i.e. the size of the 
synthetic aperture. The larger aperture results in a higher 
azimuth resolution at the cost of azimuth scene size.