THE 1998 SARNO (ITALY) LANDSLIDE FROM SAR INTERFEROMETRY Andrea Arturi (1) , Fabio Del Frate (1) , Emanuele Lategano (1) , Giovanni Schiavon (1) , Salvatore Stramondo (2) (1) Università Tor Vergata, DISP, Via del Politecnico 1, I-00133 Rome, Italy, schiavon@disp.uniroma2.it (2) Istituto Nazionale Geofisica e Vulcanologia, Via di Vigna Murata 605, I-00143 Rome, Italy, stramon@ingv.it Keywords: InSAR, pyroclastic flow, map-derived DEM, phase unwrapping ABSTRACT The SAR Interferometry is a tecnique for measuring the topography of surface and its change through the phase component of a coherent radar signal [1]. This paper reports on the results of the SAR Interferometry application to the study to the Sarno landslide. Two ERS-1/2 tandem pairs acquired over the Sarno area after the 1998 landslide have been processed to generate a SAR DEM. Due to the strong topographic relief of the study area, to avoid or limit layover and shadowing, we used either an ascending or a descending tandem pair. A DEM generated by means of two ERS1/2 tandem pairs has been compared with a topographic map derived DEM dated 1997 allowing the identification of the areas mostly affected by the landslide. The external DEM has been used because no ERS tandem pairs acquired before the disaster were available to produce a synthetic one. 1 INTRODUCTION SAR interferometry (InSAR) technique has been successfully applied to study and follow the temporal evolution of landslide events ([2] [3] [4] [5] [6]). On May 4th - 5th , 1998 about 150 landslide movements succeeding in 10 hours, from 2 to 12 p.m. hit an area of 75 km 2 near Naples (Italy), in the cities of Sarno, Siano and Bracigliano (in the district of Salerno) and in the city of Quindici (Avellino) (Fig.1). This event caused several victims and shocked the entire nation for its alarming proportions. Actually a considerable part of Italian territory is affected by hydrogeological hazard and the use of remote sensed data like SAR offers an important tool for monitoring and studying these kind of events. The mountainous belt of Campania Region surrounding the Vesuvio are interested by characteristic landslide phenomena due to the pyroclastic deposits produced by the explosive and effusive eruptive activity and left on the limestone relief. May 4th-5th 1998 the landslide was favoured by a strong atmospheric perturbation that reached the highest values in the area comprised in Sarno, Quindici, Siano, Bracigliano and Lauro territories. Pluviometers, 40 km far from the landslide area, did not recorded particularly intense rains to confirm the very spatially limited extension of the perturbation (Fig.2). Meteoric waters (rain) saturated the pyroclastic low-coherent soil, and reached the carbonatic layer where they generated subsurface water streams. Moreover, the abandoned anthropic terracing could not develop its role of collecting meteoric waters. These produced the separation of the pyroclastic terrain from the underneath carbonatic layer, and generated the pyroclastic flow. Following meteoric events the full pyroclastic thickness has been rapidly moved on the slope, involving also the vegetation cover. In November 1997 the same area had still been struck by less dramatic landslide events. ____________________________________________________________ Proc. of FRINGE 2003 Workshop, Frascati, Italy, 1 – 5 December 2003 (ESA SP-550, June 2004) 11_stramon