DInSAR SBAS data processing in the southern Andes: The Copahue-Agrio Caldera study case

EUILLADES, P.A.; VÉLEZ, M.L.; MELJEM, M.; CASELLI, A.; MARTINEZ DIAZ, J.J,

Santiago de Chile

Conferencia; . 4th Alexander von Humboldt International Conference - The Andes: Challenge for Geosciences.; 2008

Asoc Geol Chile

The Copahue volcano (37º 51.35´S 71º 10.2´W, 2977 m.s.n.m) is an active andesitic to basatic-andesitic stratovolcano nested on the western rim of Caviahue Caldera. This area is located at the border between Chile and Argentina, in the Southern Andean Volcanic Zone. The volcano summit has nine craters aligned in N60ºE direction, the easternmost is presently active with an acid hot lake (Caselli et al., 2005). The acid crater lake and acid hot springs are the surface expressions of an extensive volcanicmagmatic hydrothermal system. The evolution of the crater lake fluids during the twentieth century suggest a gradual awakening of Copahue, and future activity can be expected (Varekamp et al., 2001). This work’s main objetive is to present the strategy adopted to obtain DInSAR deformation time series of the Copahue-Agrio Caldera (CAC). We found two main problems related to DInSAR processing. The first one is a dramatic loss of interferometric coherence during the winter season. The second one is a strong atmospheric pattern always present, which make the single interferograms extremely difficult to interpret. The SBAS (Small Baseline Subsets) approach (Berardino et al., 2002) is particularly suitable to process the CAC area. It allows to obtain dense coverage deformation maps in a site where point scatterers are rather scarce. Furthermore, it implements an efficient atmospheric screen phase filtering step in post-processing. We analised the origin of the remaining problem, i.e. winter season coherence loss. It was attributed to heavy snow coverage, that remains usually between june and october. We solved the problem excluding selected images from the dataset. Selection criteria is based in snow coverage analysis from archived optical images. As a result, we succesfully processed a set of 16 ascending orbit SAR scenes, acquired by the ENVISAT ASAR sensor operating in mode IS2 and VV polarization. Time span is between December 2002 and April 2006. We remark that the complete dataset is composed of 28 scenes, acquired in the same period.We obtained deformation time series and deformation mean velocity maps covering a significant portion of the AOI.