PSInSAR validation by means of a blind experiment using dihedral reflectors

Fabrizio Novali(1) , Alessandro Ferretti(1) , Claudio Prati(2) , Fabio Rocca(2) , Giuliano Savio(1) , and Sergio Musazzi(3)

(1) Tele-Rilevamento Europa - T.R.E. s.r.l., Via Vittoria Colonna 7, 20149 Milano, Italy
(2) Politecnico di Milano, Piazza L. da Vinci 32, 20133 - Milano, Italy
(3) Centro Elettrotecnico Sperimentale Italiano - CESI, Via Rubattino 54, 20134 Milano, Italy


As well known, the Permanent Scatterers (PS) technique is an advanced tool for processing series of interferometric SAR data aiming at millimetric precision ground deformation mapping. Even if the potential of this approach have been proved in several application ranging from urban subsidence monitoring to landslide surveying in Alpine region, allowing to consider the PS Techniques an operation surveillance tool, there exist areas where no natural PSs are available. In principle, the problem can be solved by deploying a few artificial reflectors where no natural ones are available. However, the long term (years) mechanical stability of the reflectors as well as their Radar Cross Section (RCS) and multi-platform capability should be assessed. In order to perform a comprehensive validation of the PSInSAR approach using artificial reflectors and to assess the limits of its applicability, a blind experiment has been carried out in cooperation with the Centro Elettrotecnico Sperimentale Italiano (CESI)), in the frame of a research activity financed by the public fund for the Italian Electric System. Two couples of dihedral reflectors have been deployed 30m apart on the roof of the CESI offices and pointed so that a couple provide a good RCS for the ascending acquisition mode, while the other couple for the descending acquisitions. Moreover, the two couples have been pointed so to be visible in both Envisat and Radarsat acquisitions. Dihedral reflectors have been preferred to the usual thriedral corner reflectors with the same RCS for their smaller size and thus a greater mechanical stability. The aim of the experiment was to move one couple of dihedral reflectors of a few millimetres from one acquisition to the other along both vertical and East-West direction, and to compare these displacement with those estimated by means of the PS Technique applied to ascending and descending data. In this work, the results of the one year experiment carried out using a series of more than 15 Radarsat and 5 Envisat (ascending and descending) data will be shown; this allow the comparison of the estimated time series with the imposed motion, and to draw some quantitative figure on the precision and accuracy of the Line of Sight estimated displacement as well as on the sensitivity of the satellite to pure horizontal and vertical movement of the target.


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