Landslide warnings from satellites may save lives (Forwarded)

ESA News
http://www.esa.int

4 February 2004

Landslide warnings from satellites may save lives

As winter rains come, thousands of square kilometres of territory across Europe's
heart face a looming threat: steep slopes and waterlogged soils combine to trigger
landslides.

A build-up of groundwater within a slope increases its weight and decreases its
cohesiveness, weakening the slope's ability to resist the remorseless pull of
gravity. The heavy earth flows downward. For all in the path of a landslide the
results are devastating, and frequently lethal.

"In Italy, landslides have claimed an average of 54 victims per year during the last
half century," says Nicola Casagli of Italy's National Group for Hydro-geological
Disaster Prevention (GNDCI),a research network working with Italy's Civil
Protection Department.

"The extreme rainfall of our climate, our mountainous geography and recent
uncontrolled urbanisation of unstable land makes us one of the countries most
affected by landslide hazards. The total cost of direct damage done by Italian
landslides is estimated at between one and two thousand million Euro per year."

Very gradual ground shifts are known to precede more major landslides. Often
these are on a scale of millimetres -- too slight to even be noticed by local
observers, but enough to be detected via satellite using a powerful technique
called radar interferometry.

It involves mathematically combining multiple radar images of the same site --
acquired using instruments such as the Synthetic Aperture Radar (SAR) aboard
ESA's ERS spacecraft -- in such a way that tiny changes in the landscape
occurring between images are highlighted.

This technique is the basis of a new project called Service for Landslide
Monitoring (SLAM), enabling landslide susceptibility mapping across parts of
Italy and Switzerland, two of the European countries most under threat. GNDCI is
one of three national-level users working with SLAM, along with Italy's Ministry
of the Environment and Switzerland's Federal Office for Water and Geology
(FOWG).

"Surface movements assessed over wide areas are one of the best indicators of
landslide activity, and can be employed for risk forecasting," added Casagli.
"Extremely slow movements usually occur for several weeks or months before a
sudden collapse."

Trial services are being provided across Italy's Arno river basin as well as a
section of the Campania region. In Switzerland the service covers the eastern
Valais and Berne cantons.

"Our interest is to have a tool evaluate landslides and mass displacements all
across the Swiss Alps," explains Hugo Raetzo of FOWG. "About 8% of Swiss
territory is vulnerable to landslides, making up thousands of square kilometres.
The annual landslide frequency varies with the weather -- heavy rainfall can
potentially re-accelerate existing landslides."

Three different service products are available: a large-scale Landslide Motion
Survey identifying areas affected by landslides across an entire river basin, a
reduced-scale Landslide Displacement Monitoring measuring ground deformation
over particular sites of interest, and Landslide Susceptibility Mapping which
merges the previous data products with thematic maps of land use, slope,
geomorphology and other relevant parameters to provide geological hazard maps.

More than a decade's worth of ERS data archives are being exploited to derive
SLAM products. These products disclose new and essential information to the
institutions charged with landslide risk and hazard management. Benefits from the
service include the identification and characterisation of displacements both
known and previously unknown and the verification of remedial interventions
performed in the past to stabilise particular landslides.

The SLAM service is being formally implemented in February and will run until
the end of this year. It is entirely funded as part of ESA's Data User Programme
and is carried out by an international consortium led by Planetek Italia with five
other partners: Tele-Rilevamento Europa, Gamma Remote Sensing, Spacebel,
Geotest and Florence University.

Related articles

* FRINGE scientists use radar vision to see the Earth move
http://www.esa.int/esaSA/SEM913VZJND_earth_0.html
* All that glitters: The first ERS/Envisat interferogram
http://www.esa.int/esaSA/SEM97H5V9ED_earth_0.html

Related links

* What is a landslide?
http://landslides.usgs.gov/html_files/nlic/page5.html
* SLAM project sheet on Data User Element website
http://dup.esrin.esa.int/projects/summaryp52.asp
* SLAM website
http://www.slamservice.info/
* Italian Ministry of the Environment
http://www.minambiente.it/Sito/setto...t/Home_SDT.asp
* Swiss Federal Office for Water and Geology
http://www.bwg.admin.ch/e/index.htm
* Italian National Group for Hydro-geological Disaster Prevention
http://www.gndci.it/
* Arno River Basin Authority
http://www.arno.autoritadibacino.it/

[NOTE: Images supporting this release are available at
http://www.esa.int/export/esaSA/SEM0...D_earth_1.html ]