Perspective of Sentinel-1 for INSAR Applications: towards a global phase calibration
Rocca, Fabio1; Hanssen, Ramon2; Monti Guarnieri, Andrea3
1Politecnico, ITALY; 2Delft University of Technology, NETHERLANDS; 3Politecnico di Milano, ITALY

Since the onset of its systematic applications, begun with the orbiting of ERS 1 in 1991, InSAR methodology is progressively becoming an usual tool to measure subsidence and slow ground motion from a radar satellite. New applications to the oil and gas industry, to the measurement of motion of long infrastructures, to the understanding of the behavior of bridges and urban structures, to the achievement of a 3D tomographic interpretation using multiple baseline acquisitions will be discussed.

Further results have also been obtained in non-urbanized areas exploiting the so called SqueeSAR approach, where also partially coherent and distributed scatterers contribute to the measurement of the motion on an denser grid, that becomes however time varying. The use of Numerical Weather Prediction models has been amply studied and even if the present results are mixed, still the final conclusion is bound to be positive in that NWP and InSAR will synergize, even if the turbulent component of the water vapor distribution remains unreachable from NWP and easily visible and highly significant in InSAR images.

The status of the art of the applications of InSAR will be presented in the talk, banking on the exceptional character of the Sentinel 1 A/B surveys. In its Interferometric Wide Swath mode this satellite couple will acquire every 6 days long strips of data (up to thousands of Kilometers), on a 250 km wide swath.

Finally, the systematic use of the Persistent Scatterers methodology will allow new calibration methods that should achieve phase calibration as well as good amplitude calibration together with antenna pattern and satellite roll corrections. In fact, the long term stability of millions of scatterers visible in each long acquisition will allow the creation of significant data bases where all their scattering characteristics together with their topography will be stored. Even if most will change with time, still the very favorable statistics will allow a systematic data calibration [1]: this entails the correction of orbital drifts, earth tides, Atmospheric Phase Screens, and satellite drifts. Further, the use of the TOPS scan technique needs a quite precise azimuthal coregistration of the scans, up to a very small (hundredth) fraction of the azimuth resolution. This will also be achievable using this methodology.

Similar results can also be obtained in a feed forward mode, using all the necessary information (APS, earth tides, precise positioning, etc.) and thus achieving imaging geodesy from space [2]. The availability of the PS makes it possible to achieve a similar result with a higher computational effort, but on wide areas.

The availability of phase calibrated data sets will allow an easy combination of the signatures of the scatterers, identifying their possible motion effects.

The potential of integrating the Sentinel-1 InSAR results in a global geodetic reference datum, by the physical link to GNSS network stations, will allow for an even wider range of applications. This datum connection is particularly important when InSAR data are being used in concert with other geodetic observations, and when long term physical processes (e.g. interseismic and loading) need to be estimated.

[1] D. D’Aria, D. Giudici, S. Mancon, A. Monti Guarnieri, S. Tebaldini, Experimental assessment of the PS-cal technique over COSMO-SKYMED high resolution SAR data, Proceedings IGARSS 2012, pp. 3293 ff.

[2] X. Cong; Balss, U.; Eineder, M.; Fritz, T. , Imaging Geodesy-Centimeter-Level Ranging Accuracy With TerraSAR-X: An Update, Geoscience and Remote Sensing Letters, IEEE Volume: 9 , Issue: 5 , 2012 , Page(s): 948 - 95