The 1998 Sarno (Italy) landslide from SAR Interferometry
Salvatore Stramondo(1) and Andrea Arturi(2)
Istituto Nazionale di Geofisica e Vulcanologia,
Via di Vigna Murata, 605,
00143 - Rome,
(2) Universita Tor Vergata, Via del Politecnico 1, 1-00133 Rome, Italy
On May 4th - 5th , 1998 about 150 landslide movements succeeding in 10
hours, from 2 to 12 p.m. hit an area of 75 km2 near Naples (Italy), in
the cities of Sarno, Siano and Bracigliano (in the district of Salerno)
and in the city of Quindici (Avellino). 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.
Meteoric waters (rain) saturated the pyroclastic low-coherent soil, and
reached the carbonatic layer where they generated subsurface water
streams. Besides 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
We present results of SAR Interferometry application to the study of
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. The two tandem pairs are characterized by a
perpendicular baseline of 339 m such to have an ambiguity height of
about 26 m, and 245 m, with an ambiguity height of 36 m. We used as
reference a topographic map derived DEM dated 1997. The external DEM
has been used because no ERS tandem pairs acquired before the disaster
were available to produce a synthetic one. The resulting SAR DEM has
been obtained by merging the two single pair SAR DEMs, also considering
a weighting function based on the coherence of each interferometric
pair. After coregistration, the map of the differences between the two
DEMís has been generated. Except for the portions of the SAR
interferogram characterized by low coherence and layover, where
processing do not produce reliable results, the areas affected by the
landslide have been identified as those showing the highest differences.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,