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The TerraSAR-X (copyright) mission, launched in 2007, carries a new X-band Synthetic Aperture Radar (SAR) sensor
optimally suited for SAR interferometry (InSAR), thus allowing very promising application of InSAR techniques
for the risk assessment on areas with hydrogeological instability and especially for multi-temporal analysis, such
as Persistent Scatterer Interferometry (PSI) techniques, originally developed at Politecnico di Milano. The
SPINUA (Stable Point INterferometry over Unurbanised Areas) technique is a PSI processing methodology
which has originally been developed with the aim of detection and monitoring of coherent PS targets in non
or scarcely-urbanized areas. The main goal of the present work is to describe successful applications of the
SPINUA PSI technique in processing X-band data. Venice has been selected as test site since it is in favorable
settings for PSI investigations (urban area containing many potential coherent targets such as buildings) and
in view of the availability of a long temporal series of TerraSAR-X stripmap acquisitions (27 scenes in all).
The Venice Lagoon is affected by land sinking phenomena, whose origins are both natural and man-induced.
The subsidence of Venice has been intensively studied for decades by determining land displacements through
traditional monitoring techniques (leveling and GPS) and, recently, by processing stacks of ERS/ENVISAT SAR
data. The present work is focused on an independent assessment of application of PSI techniques to TerraSAR-X
stripmap data for monitoring the stability of the Venice area. Thanks to its orbital repeat cycle of only 11 days,
less than a third of ERS/ENVISAT C-band missions, the maximum displacement rate that can be unambiguously
detected along the Line-of-Sight (LOS) with TerraSAR-X SAR data through PSI techniques is expected to be
about twice the corresponding value of ESA C-band missions, being directly proportional to the sensor wavelength
and inversely proportional to the revisit time. When monitoring displacement phenomena which are known to
be within the C-band rate limits, the increased repeat cycle of TerraSAR-X offers the opportunity to decimate
the stack of TerraSAR-X data, e.g. by doubling the temporal baseline between subsequent acquisitions. This
strategy can be adopted for reducing both economic and computational processing costs. In the present work,
the displacement rate maps obtained through SPINUA with and without decimation of the number of Single
Look Complex (SLC) acquisitions are compared. In particular, it is shown that with high spatial resolution SAR
data, reliable displacement maps could be estimated through PSI techniques with a number of SLCs much lower
than in C-band.
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