Department of Earth Sciences CENTRE OF COMPETENCE OF THE CIVIL PROTECTION DEPARTMENT PRESIDENCY OF THE COUNCIL OF MINISTERS Radar and InSAR techniques Nicola Casagli, Giacomo Falorni, Valeria Pancioli
Scheme of presentation Materials and methods Satellite SAR interferometry Ground-based SAR interferometry Applications Inventory and motion survey Monitoring and interpretation Rapid mapping Instant mapping Failure forecasting Early-warning
SATELLITE SAR INTERFEROMETRY
Radar Satellites SAR = Synthetic Aperture Radar θ=23
Radar satellites
Range (R) SAR images Azimuth (Az) layover Vajont landslide shadow Ground range Lambert backscattering Backscattered Energy [l cos ( i - )] Representation of backscattered energy Geometrical distorsions: foreshortening, layover, shadow
SAR Interferometry (InSAR) Acquisition at time 1 Radar interferometry is based on the quantitative comparison between paired complex and coherent SAR images taken at different times i T R f i R T interferometric phase f Interferogram of the Vajont landslide r - r = Acquisition at time 2 R i T f = DISP + TOPO + ATMO + NOISE Different techniques exist to separate the phase contribution due to ground displacements
SAR interferometry Time T 0 Time T 0 + t R 1 R 1 = R 2 r 1 acquisition 2 acquisition Permits to assess ground deformations with centimetric accuracy Laion Landslide
interferometric phase Differential interferometry (DInSAR) SAR Image (ERS) differential interferogram Detection of ground movements occurred in the time span between two acquisitions with an accuracy of a small fraction of wavelength Satellite: Acquisitions from different positions (baseline >0) = TOPO + MOV Ground-based: Acquisitions from the same position (baseline =0) = MOV
tempo Permanent Scatterers technique pixel by pixel analysis ESA - ERS San Francisco International Airport multi-image processing San Francisco Bay Processing technique of SAR images which allows to assess deformations with millimetric accuracy on single specific points (PS), coincident with highly reflective elements on the ground surface 35 giorni 100 Km Dataset of SAR images 100 Km
Persistent Scatterers Interferometry (PSI) SBAS (CNR-IREA-NA) Sparse phase unwrapping (SU-DIFSAR) Maratea
GROUND-BASED SAR INTERFEROMETRY
Ground based SAR interferometry Portable SAR apparatus known as LISA (Linear Synthetic Aperture Radar), developed by the Joint Research Centre of the European Commission
LiSA
European Commission Joint Research Centre Ground-based InSAR target area Continuous-wave stepped-frequency (CW-SF) radar based on a Network Analyser (NWA) operating in the frequency band 17.0-17.1 GHz Tx Rx sled linear rail 2.8m source NWA computer The synthetic aperture is obtained sliding the antennas along a linear rail
phase wrapping Interferometry Image 1 Interferogram (phase difference) 5 Image 2 1 2 3 4 LOS displacement (mm) 1: Flank of Sciara del Fuoco (stable) 2 and 3: Sciara del Fuoco slope 4 and 5: crater
Interferogram on DTM
INVENTORY AND MOTION SURVEY
total: 327 942 PS PS ERS descending 1992-2002
total: 263 321 PS PS ERS ascending 1992-2002
27 270 mapped landslides 8.8 % landslide density Landslide inventory map 74% earth slides and flows 19% shallow landslides and creep 5% debris flows 2% others
Area-frequency distribution of landslides 10 4 m 2 UNDERSAMPLING LIMIT FOR MAPPED LANDSLIDES scaling law
PS and landslide map Legend Landslide polygons attiv instab quiesc PS ascending Vel (mm/y) ") -29.18 - -5.00 ") -4.99 - -3.00 ") -2.99 - -1.25 ") -1.24-1.25 ") 1.26-3.00 ") 3.01-5.00 ") 5.01-29.05 G PS_rufina Landslide lines attiv inatt PS Descending Vel (mm/y) $+ -29.18 - -5.00 $+ -4.99 - -3.00 $+ -2.99 - -1.25 $+ -1.24-1.25 $+ 1.26-3.00 $+ 3.01-5.00 $+ 5.01-29.05
Updating landslide inventory Landslide A Activity: confirmed Boundary: modified A Landslide B Activity: modified Boundary: modified B active inactive active inactive dormant active inactive dormant Landslide F Activity: modified Boundary: confirmed F Landslide C Activity: modified Boundary: modified C C E D Landslide E New detection Landslide D New detection
Activity matrix MATRIX OF ACTIVITY ERS < 2mm ERS > 2mm ENVISAT < 2 mm Stable Dormant ENVISAT > 2 mm Active (reactivated) Active (continuos)
Revised hazard area with PS information
MONITORING AND INTERPRETATION
PS RADARSAT ascending 2003-2005 Displacement = 4-12 mm/year
PS RADARSAT descending 2003-2005 Displacement= 4-8 mm/year
Comparison with multibeam bathymetry Multi-beam survey by UNIROMA1-DST (F. Chiocci) presence of canyons and submarine slope instability features (eg. scarps)
Reconstruction of the slip surface Graphical method for reconstructing the slip surface (Carter & Bentley, 1985; Cruden, 1986) used in Structural Geology Input data: position of the main scarp and displacement vectors within the landslide mass Assumption: rigid deformation within each slice (Mertie, 1947)
Prodondità (m p.c.) Prodondità (m p.c.) Reconstruction of the slip surface Sezione EF O4 V2 N1 O1 O2 N3 N4 N5 N6 N7 N8 V3 V4 V5 V6 V7 V8 Sezione CD Distanza (m) Distanza (m)
Interpolation N 0 depth (m) 250 Interpolation of multiple sections Data available only above the sea level
Extrapolation N 0 350 depth (m) Extrapolation of the sections below the sea level based on a constant reduction of the local inclination of the slip surface
Profondità Possible interpretation Sezione Porto Turistico Distanza (m) Presence of multiple slip surfaces Shallow landslide in the area of the harbour
N 0 350 depth (m b.s.l.)
Comparison with bathymetry 0 350 depth (m) Multi-beam by UNIROMA1-DST (F. Chiocci) Estimated landslide volume = 1 billion m 3 = 1 km 3
RAPID MAPPING
Cavallerizzo di Cerzeto: 7 march 2005
Satellite ERS1/2 Orbit descendent Startdate 15/09/1992 Enddate 05/01/2001 No. of images 70 No. of PS 4642
Satellite RADARSAT Orbit ascendent Startdate 18/03/2003 Enddate 26/11/2005 No. of images 38 No. of PS 7869
Ikonos image rendered on DEM and PS
Cavallerizzo di Cerzeto Initial landslide map (PAI)
Cavallerizzo di Cerzeto after photointerpretation
Cavallerizzo di Cerzeto after radarinterpretation of ERS/ ENVISAT data
Cavallerizzo di Cerzeto after radarinterpretation of RADARSAT data