IEEE Geoscience and Remote Sensing Magazine - June 2014 - 21

june 2014

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polarimetric SAR interferometry
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will be wide area observations of
crop phenology by repeated measurements of crop height over the
whole growing season [54].
To foster the development of these
and further innovative bistatic and
multistatic SAR techniques, TanDEMX will be operated in a dedicated science phase where the formation and
instrument parameters are adjusted
in accordance with the science needs.
According to the current planning,
the science phase will last from October 2014 until December 2015. Two
major configurations are foreseen,
the pursuit monostatic mode and the
bistatic mode. For both interferometric modes, an operation either in single/dual or in quad polarization using
the dual receive antenna technique
will be possible. The pursuit monostatic phase, which will last approx. 4
months, is characterized by a set of
drifting vertical baselines that range
between 0 m and 1 km. Since these
baselines are available at all latitudes
and within short time periods, they
are well suited for SAR tomography
as well as large baseline investigations
in the polar regions. The large alongBiomass (Mg/ha)
track separation between the satellites
Non Forested
enables, moreover, the observation
Water Bodies
of slow drifts and movements. The
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bistatic phase will then begin in early
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spring 2015 using a formation with
Krycklan (Boreal Forest)
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large horizontal cross-track baselines.
> 220
These baselines are well suited for the
monitoring of crop heights during
the growing season, but they can also FIgUre 15. Above ground forest biomass derived from forest height using TanDEM-X dual
serve many other applications that baseline dual polarization polarimetric SAR interferometry (Krycklan, Sweden). The estimation
demand repeated acquisitions with of forest height and biomass in X-band is, however, limited to selected areas that are characterlarge but temporally constant base- ized by less dense forest.
lines. In autumn 2015, the bistatic
and flying both satellites in a closely controlled formabaselines will be reduced to 100-300 m as required for fortion. This enables not only the acquisition of a global
est applications and along-track interferometry. While sciDEM with unprecedented accuracy, but also the demonence acquisitions will have priority during this 15-month
stration of highly innovative bistatic and multistatic SAR
period, it is nevertheless planned to acquire additional
techniques and applications. These experiments form the
data to fill gaps and further improve the quality of the
basis for future formation flying SAR missions [55], [56].
TanDEM-X DEM.
Key technologies like close formation flying, bistatic
SAR operation and synchronization, precise baseline estiVIII. CONCLUSION
mation and calibration as well as sophisticated bistatic and
The TanDEM-X mission opens a new era in spaceborne
interferometric processing chains have been implemented.
radar remote sensing. A large single-pass SAR interferomAppropriate safety mechanisms enable safe operation at
eter with adjustable baselines has been formed by adding
typical satellite distances between 120 m and 500 m. The
a second, almost identical radar satellite to TerraSAR-X
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Table of Contents for the Digital Edition of IEEE Geoscience and Remote Sensing Magazine - June 2014