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

EUILLADES, PABLO A.; VÉLEZ, LAURA; MELJEM, MISAEL; CASELLI, ALBERTO; MARTINEZ DÍAZ, JOSÉ

Santiago de Chile

Conferencia; 4th Alexander von Humboldt International Conference, The Andes: challenge for Geosciences; 2008

European Geophysical Union

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