Pixel-Offset SBAS analysis: a tool for the investigation of deformation time-series with large dynamics

Transcription

1 Pixel-Offset SBAS analysis: a tool for the investigation of deformation time-series with large dynamics F. Casu, A. Manconi, A. Pepe, M. Manzo, R. Lanari IREA-CNR Napoli, Italy casu.f@irea.cnr.it

2 Summary Small BAseline Subset algorithm is a well known technique which permits to generate deformation time series starting from a set of small baseline (spatial and temporal) interferograms. In areas characterized by large and rapid deformation dynamics, deformation can not be easily retrieved due to high fringe rates (possible PhU problems) and misregistration. A way to overcome this limitation is to exploit the amplitude information. In this work, we applied the SBAS strategy to the sequence of the range and azimuth Pixel-Offset estimates, achieved from the same set of small baseline data pairs. This approach has been tested on an ENVISAT ASAR data archive (Track 61, Frames ) related to the Galàpagos Islands, focusing on Sierra Negra caldera (Galapagos Islands). Results have been compared to continuous GPS measurements and to synthetic deformation obtained by independently modeling the interferometric phase information.

3 Key idea of the SBAS algorithm For each coherent pixel, the time-series deformation is computed by searching for an LS solution with a minimum norm constraint (the SVD method is applied).

4 Why small baseline data pairs? Small baseline InSAR interferograms are less affected by noise effects (decorrelation) and are easier to process (registration / unwrapping steps). ENVISAT Amplitude: Galàpagos Baseline: 40m Baseline: 1000m

5 Further constraints: deformation amount Co-Registration problems Possible PhU problems Conventional InSAR Small Deformation amount Large

6 >3 Conventional SBAS-InSAR results: Galàpagos cm/yr <-3 Isabela 26 ASAR Envisat scenes, T61 In collaboration with F. Amelung October, 21st 2005 Fernandina Azimuth? Sierra Negra

7 Pixel-Offset SBAS: key idea We exploit the amplitude information in order to retrieve deformation in areas characterized by large dynamics. In particular, we apply the well known SBAS approach to the Pixel-Offsets retrieved via cross-correlation of the amplitude relevant to small baseline SAR image pairs. Note that, we may directly use the already registered SAR image pairs computed to generate the SBAS-InSAR time series.

8 Why small baseline data pairs? Perp. Bas. 40m Perp. Bas. 1000m

9 Pixel-Offset SBAS (PO-SBAS): good pixels vs. baseline Small Baseline Constraint Quadratic relationship

10 >3 PO-SBAS results: Galàpagos cm/yr <-3 Conventional SBAS-InSAR mask Pixel-Offset SBAS mask Range Azimuth (mostly North)

11 Validation of RANGE displacements: SAR vs GPS time series GV01 GV03 GV04 GV05 GV02 GV06 Δ SAR - GPS GPS data from Chadwick, et al. 2006, Geology

12 Validation of AZIMUTH displacements: SAR vs GPS time series GV04 GV03 GV02 Δ SAR - GPS GPS data from Chadwick, et al. 2006, Geology

13 Validation of displacements: SAR vs GPS baseline change GV04 GV03 GV06 GPS Estimates, from Geist, et al. 2008, Bull. of Volc.

14 PO-SBAS results validation: Modelling the surface deformation Volume change of a sill-shaped (Okada) source, source parameters in agreement with Geist et al., 2008 Length (km) Width (km) Depth (km) Dip (deg) Strike (deg) 12/07/ /11/

15 PO-SBAS results: Afar >10 cm/yr < ASAR Envisat scenes In collaboration with T. Wright

16 Conclusions and further developments We present the results achieved by exploiting the amplitude information in order to retrieve deformation in areas characterized by large dynamics (eg. Volcanic and Seismogenic areas). We show that the well known SBAS approach can be successfully applied also to the Pixel-Offsets retrieved via cross-correlation of the amplitude relevant to small baseline SAR image pairs. We obtain deformation time series relevant to displacements in both range and azimuth direction in areas where no interferometric phase could be exploited; the achieved accuracy is of about 1/20 of pixel. The exploitation of higher resolution SAR images (TERRASAR-X, COSMO-Skymed) is envisaged. The retrieved offset information can be further used in order to properly register the analyzed data pairs, thus restoring the possibility of generating interferogram sequences, following Sang-Ho Yun et al., GRL, 2007.

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