Radar and InSAR techniques

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1 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

2 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

3 SATELLITE SAR INTERFEROMETRY

4 Radar Satellites SAR = Synthetic Aperture Radar θ=23

5 Radar satellites

6 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

7 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

8 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

9 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

10 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

11 Persistent Scatterers Interferometry (PSI) SBAS (CNR-IREA-NA) Sparse phase unwrapping (SU-DIFSAR) Maratea

12 GROUND-BASED SAR INTERFEROMETRY

13 Ground based SAR interferometry Portable SAR apparatus known as LISA (Linear Synthetic Aperture Radar), developed by the Joint Research Centre of the European Commission

14 LiSA

15 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 GHz Tx Rx sled linear rail 2.8m source NWA computer The synthetic aperture is obtained sliding the antennas along a linear rail

16 phase wrapping Interferometry Image 1 Interferogram (phase difference) 5 Image LOS displacement (mm) 1: Flank of Sciara del Fuoco (stable) 2 and 3: Sciara del Fuoco slope 4 and 5: crater

17 Interferogram on DTM

18 INVENTORY AND MOTION SURVEY

19 total: PS PS ERS descending

20 total: PS PS ERS ascending

21 mapped landslides 8.8 % landslide density Landslide inventory map 74% earth slides and flows 19% shallow landslides and creep 5% debris flows 2% others

22 Area-frequency distribution of landslides 10 4 m 2 UNDERSAMPLING LIMIT FOR MAPPED LANDSLIDES scaling law

23 PS and landslide map Legend Landslide polygons attiv instab quiesc PS ascending Vel (mm/y) ") ") ") ") ") ") ") G PS_rufina Landslide lines attiv inatt PS Descending Vel (mm/y) $ $ $ $ $ $ $

24 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

25 Activity matrix MATRIX OF ACTIVITY ERS < 2mm ERS > 2mm ENVISAT < 2 mm Stable Dormant ENVISAT > 2 mm Active (reactivated) Active (continuos)

26 Revised hazard area with PS information

27 MONITORING AND INTERPRETATION

29 PS RADARSAT ascending Displacement = 4-12 mm/year

30 PS RADARSAT descending Displacement= 4-8 mm/year

31 Comparison with multibeam bathymetry Multi-beam survey by UNIROMA1-DST (F. Chiocci) presence of canyons and submarine slope instability features (eg. scarps)

32 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)

33 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)

34 Interpolation N 0 depth (m) 250 Interpolation of multiple sections Data available only above the sea level

35 Extrapolation N depth (m) Extrapolation of the sections below the sea level based on a constant reduction of the local inclination of the slip surface

36 Profondità Possible interpretation Sezione Porto Turistico Distanza (m) Presence of multiple slip surfaces Shallow landslide in the area of the harbour

37 N depth (m b.s.l.)

38 Comparison with bathymetry depth (m) Multi-beam by UNIROMA1-DST (F. Chiocci) Estimated landslide volume = 1 billion m 3 = 1 km 3

39 RAPID MAPPING

41 Cavallerizzo di Cerzeto: 7 march 2005

43 Satellite ERS1/2 Orbit descendent Startdate 15/09/1992 Enddate 05/01/2001 No. of images 70 No. of PS 4642

44 Satellite RADARSAT Orbit ascendent Startdate 18/03/2003 Enddate 26/11/2005 No. of images 38 No. of PS 7869

46 Ikonos image rendered on DEM and PS

47 Cavallerizzo di Cerzeto Initial landslide map (PAI)

48 Cavallerizzo di Cerzeto after photointerpretation

49 Cavallerizzo di Cerzeto after radarinterpretation of ERS/ ENVISAT data

50 Cavallerizzo di Cerzeto after radarinterpretation of RADARSAT data

Exploitation of historical satellite SAR archives for mapping and monitoring landslides at regional and local scale

Exploitation of historical satellite SAR archives for mapping and monitoring landslides at regional and local scale (A. Ferretti (TRE), A. Tamburini (TRE), M. Bianchi (TRE), M. Broccolato (Regione Valle