N. Casagli, F. Catani, G.Luzi, L. Guerri: Univ. Florence, Earth Sciences Department

D. Tarchi: EU Commission JRC –IPSC

D. Leva: LisaLab Ltd A JRC spin-off company

Monitoring deformations through Ground-Based radar interferometry

Department of Earth Sciences CENTRE OF COMPETENCE OF THE CIVIL PROTECTION DEPARTMENT

PRESIDENCY OF THE COUNCIL OF MINISTERS

Presentation outline •  Introduction to Ground Based radar

interferometry

•  The LiSA GB SAR system at Stromboli •  The 2003 data collection:

•  effusion phase •  5 April explosion

•  The 2007 data collection: •  inflation in the pre-effusive phase •  bulging and vent opening • 15 March explosion

A radar transmits and receives e.m. wave in the Microwave portion of the em. spectrum

c=⋅ fλKu band

Radar signal is slightly affected by atmospheric propagation MW sensors work when the optical ones are blind

Low attenuation

•  In Remote Sensing we want to observe natural surfaces with fine spatial resolution.

•  Conventional RADAR were born for detecting and ranging targets and suffer from a coarse spatial resolution limited by antenna dimension and radar-target distance

•  Synthetic Aperture Radar SAR is a tool to collect radar images from large distances with high spatial resolution: a few meters from hundreds of kilometres.

Radar

A target

The map

A wave travels transferring the configuration of a physical parameter (e.m field, sound, a seismic deformation..…) with a velocity c. It is characterized by: amplitude A, wavelength λ, frequency f and phase θ and can generates specific phenomena as: interference and diffraction

Phase strongly affects waves interaction

A λ

f=number of cycles per time unit

c=⋅ fλ

c= light velocity ~ 3.108 m/s

To perform interferometry waves need a stable phase

wave

wave

interference

Basic interferometry

Two waves “in phase” yield high intensity Two waves “in quadrature” yield a null intensity Every half wavelength displacement ambiguity arises Fringes are an alternating of bright and dark lines due to interference: phase ranges only from –π to+ π

In phase

Quadrature

When errors are negligible a simple relationship between the displacement and the measured phase:

ϕπλΔ=Δ

4R

To retrieve phase value exceeding half phase Cycle, measured phase must be unwrapped.

Azimuth resolution

Pk

Azimuth length: L

ΔXa (Np step)

Rn,k

n

Main benefits from GB observations: •  Accurate motion •  Frequency of the observation very high (<hour) •  Zero spatial baseline among images

Range resolution

Azimuth resolution BcR2

=Δ

L2λ

ϑ =Δ

SAR imaging: the Ground Based approach

B = bandwidth L = scan length λ = wavelength

Focalization improves azimuth resolution

)(

1 1

))(4(2 )(1)( nj

n

k

n

i

Rcf

iknkpf

n enIeERnn

PIp f

onki

ϕπ

== ∑ ∑= =

Focalization alghorythm

The SAR power image of a brigth spot (an oriented metal disk)

Transceiver: a Continuous-wave stepped-frequency (CW-SF) radar based on a Vectorial Network Analyser (VNA)

ϕλπ

jli

Rj

lili eseaInoiseli

,

4

,,

,

==⎥⎦

⎤⎢⎣

⎡ Φ−

A SAR image is represented through a matrix of complex numbers

The amplitude of a pixel sil is related to backscattering of the illuminated area The phase ϕ is related to propagation path + noise due to other factors.

RADAR

When a Digital Elevation Model is available we can project the radar image on it

2d Amplitude image

3d Amplitude image

Topography

Pi

B≠0 Δφ∝(4π/λ) hr

Master Image Slave Image

φ=arg[MS*]

R

iRj

ieaRt 14

1),(M λπ

−=

iRj

ieaRt 24

2),(S λπ

−=

ϕλπ

ji

RRj

iii eseaasinoiseii

==⎥⎦

⎤⎢⎣

⎡ Φ−− ))(4*,2,1

,12

Displacement

B~0 Δφ=(4π/λ) ΔR

B=Baseline

Interferometry provides sub-wavelength sensitivity

Interferometric Phase φ:

Measured differential phase can be affected by some “decorrelation sources”. In GB case :

Phase

nt displacemeatmosfericgeometricscatteringalinstrument φφφφφφ ++++=

=

Interferogram

Zero baseline

*

Time= t0

Time= t0+Δτ

The amplitude of the conjugate product is related to coherence

Phase Wrapping: Large displacement generates fringes

Decorrelation: Rapid motion causes “salt & pepper” texture

Coherence, Γ, ( 0 <Γ <1) gives an estimate of the error in measured differential phase

Phase wrapping and decorrelation

InGrID-LiSA

Interferometric Ground-based Imaging Deformeter Linear Synthetic Aperture Radar Ingrid

Bergman on the set of the movie “Stromboli” (1949)

2002-2003 eruption Landslides on SDF on 30 December 2002

Photo INGV Catania (2003) Courtesy of Sonia Calvari

Heli-platform

Radar installation

Data collection

centre

Wireless connection

Heli-platform

Optical cable

16

System set-up

17

Continuous-wave stepped-frequency (CW-SF) radar based on a Network

Analyser (NWA) operating in the frequency band 17.0-17.1 GHz

Ground-based InSAR

The synthetic aperture is obtained sliding the antennas along a linear rail

2.8m

target area

Rx Tx

sled

source NWA

computer

linear rail

:

European Commission Joint Research Centre

Measurement parameters

•  Frequency range: 17.0 – 17.10 GHz

•  Frequency points : 1601 •  Polarization: VV •  transmitted power:

300 mW (25 dBm)

•  Synthetic Aperture: 3.0 m

•  Step: 5 mm •  Azimuth points : 601 •  Time range: 12 min

•  Image number: ca. 120 per day

•  distance: 650 m •  Spatial Resolution: 1.0 m x ca. 1.5 m •  Accuracy: < 0.5 mm

Acquisition of raw data

Network Analyzer

First step:

Second step:

Interferometry Image 1

Image 2

Interferogram (phase difference)

1 2

3

4

5

phas

e w

rapp

ing

LOS displacem

ent (mm

)

1: Flank of Sciara del Fuoco (stable) 2 and 3: Sciara del Fuoco slope 4 and 5: crater

1 2

3

4 5

Lava flow No.1

Lava flow No.2

Lava flow No.3

Observed scenery February 2003

Power image

1 2

3

4

5

SHADOW

LOW REFLECTIVITY

HIGH REFLECTIVITY

SdF velocity history since 2003

Negative velocity = shortening Positive velocity = lengthening

Crater velocity history since 2003

Negative velocity = shortening Positive velocity = lengthening

SdF velocity history since 2003

eruption

eruption

Crater velocity history since 2003

eruption

eruption

www.ct.ingv.it (Jan 2003) www.ct.ingv.it (Jan 2003)

Feb. 2003

Lava flows

Interferogram 12’

Lava flow 3 mm in 12’ (15 mm/h)

LOS displacem

ent (mm

) Interval:

12’

Start: Febr. 21

15:21

End: Febr. 21

15:33

Interval: 12’

Start: April 1 07:47

End:

April 1 07:59

Rapid lava flow (decorrelated)

Interferogram 12’

LOS displacem

ent (mm

) Interval:

1h

Start: March 1 07:36

End:

March 1 08:36

Rapid lava flow

Slope movement (1.5 mm/h)

Interferogram 1h

LOS displacem

ent (mm

) Interval:

1h

Start: April 1 15:00

End:

April 1 16:00

Rapid lava flow

Slope movement (2.2 mm/h)

Interferogram 1h

LOS displacem

ent (mm

) Interval:

1h

Start: April 27 12:05

End:

April 27 13:05

Slope movements disturbed by lava flows

Interferogram 1h

LOS displacem

ent (mm

)

Slope movements disturbed by lava flows

Interval: 1h

Start: December

01 12:05

End:

December 01

13:05

Interferogram 1h

Slope movement 17 mm in 1h50’

(2.2 mm/h)

Lava flows

LOS displacem

ent (mm

) Interval: 1h 50’

Start:

Febr. 21 19:10

End:

Febr. 22 03:02

Interferogram 1h

March 2

April, 25

February

α

β

δ

Slope movements on SdF

Slope movements on the crater

Rockfalls inside the

crater

LOS displacem

ent (mm

) Interval:

12h

Start: April 13 01:20

End:

April 13 13:20

Slope movements disturbed by lava flows (phase ambiguity)

Slope movement (3 mm/day)

Landslides

Interferogram 12h

Interferogram 24h

LOS displacem

ent (mm

) Interval:

24h

Start: April 11 03:55

End:

April 12 13:55

Slope movements disturbed by lava flows (phase ambiguity)

Slope movement (3 mm/day)

Diffused landslides

LOS displacem

ent (mm

) Interval:

48h

Start: March 30

13:45

End: April 01 13:45

Slope movement 6 mm in 48h (3 mm/day)

Decorrelation due to lava flows

Rockfalls

Diffused landslides

Interferogram 48h

LOS displacem

ent (mm

) Interval: 75h 07’

Start:

April 26 05:03

End:

April 29 08:10

Slope movement 7 mm in 75h (2 mm/day)

Decorrelation

Rockfalls

Diffused landslides

Interferogram 75h 07’

Interval: 7 days 05’

Start:

December 01

13:54

End: December

08 13:59

LOS displacem

ent (mm

)

Decorrelation

Slope movement (0.9mm/d)

Interferogram 7d 0h 05’

Interval: 12 days 09h 45’

Start:

April 20 19:16

End:

May 05 08:10

LOS displacem

ent (mm

)

Decorrelation

Slope movement (phase ambiguity)

Interferogram 12d 9h 45’

Long period cumulated sequence

Start: 26/2 16.00 End: 28/2 09.30 Total interval: 41h 30min Interval between images: 36 min Max displacement: 35 mm Max speed: 0.84 mm/h

Deformation map on DTM

Interferogram on DTM

Explosion of 5 April 2003 08.12 GMT+1

3 m

Before

After

LOS displacem

ent (mm

) Interval: 1h 52’

Start: April 5 07:52

End:

April 5 09:44

Decorrelation over all the interferogram

Interferogram across the explosion

Ground-shacking effect

Interferogram after the explosion

LOS displacem

ent (mm

) Interval: 1h 24’

Start: April 5 09:20

End:

April 5 10:44

Slope movement (3.2 mm/h)

Slope movement (4 mm/h)

Explosion SAR sequence

Interval:06’

Start: April 5 08:07

End:

April 5 08:13

Phase in degrees

2007 eruption

27th February: lava effusion from the crater

27th February vent opening (400 m a.s.l. )

Target area (2007)

Target area (2007)

11 Jan. 2007 47 days before the

eruption

Interval: 24h 12’

Start:

13.19 GMT 2007/01/10

End:

13.32 GMT 2007/01/11

Crater velocity:

0.04 mm/h

Sciara velocity: 0.035 mm/h

26 Jan. 2007 32 days before the

eruption: acceleration in the crater area

Interval: 24h 07’

Start:

08.08 GMT 2007/01/25

End:

08.15 GMT 2007/01/26

Crater velocity:

0.10 mm/h

Sciara velocity: 0.027 mm/h

15 Feb. 2007 12 days before the

eruption: acceleration in the Sciara del Fuoco

Interval: 15h 32’

Start:

02.19 GMT 2007/02/15

End:

17.51 GMT 2007/02/15

Crater velocity:

0.50 mm/h

Sciara velocity: 1.50 mm/h

27 Feb. 2007

Eruption

Sequence of

11’ ITF

Interval: 14h 41’

Start:

00.11 GMT 2007/02/27

End:

14.52 GMT 2007/02/27

05.53 GMT

21.05 GMT

27 Feb. 2007

Power images Morphological modifications

of the crater and of the upper Sciara del Fuoco

Interval: 15h 12’

Upper:

05.53 GMT 2007/02/27

Lower:

21.05 GMT 2007/02/27

Inverse velocity method Impossibile visualizzare l'immagine. La memoria del computer potrebbe essere insufficiente per aprire l'immagine oppure l'immagine potrebbe essere danneggiata. Riavviare il computer e aprire di nuovo il file. Se viene visualizzata di nuovo la x rossa, potrebbe essere necessario eliminare l'immagine e inserirla di nuovo.

( )[ ] 11

11

1 )(1 −− −−=⇒∞= ααα ttAv fvf i

if α = 2 then: 1/v = A(tf-t)

Fukuzono (1985)

Inverse velocity plot – 27 February

ERU

PTIO

N A

ND

LA

ND

SLID

ES

Landslides of Feb.27

10.57 - 13.37 GMT

14.30 - 14.41 GMT

13.48 - 14.09 GMT

14.41 - 14.52 GMT

2007/02/27

LOS displacem

ent (mm

)

71

18.46 - 18.57 GMT 19.08- 19.19 GMT

cumulated 18.57- 19.29 GMT 19.40 -19.51 GMT

2007/02/27

LOS displacem

ent (mm

)

72

20.33 - 20.44 GMT

20.44 - 20.55 GMT 21.37 - 21.48 GMT

19.51 - 20.01 GMT

73

8-9 March: lava effusion from new vent

8-9 March 2007

Opening of a 2nd vent

Sequence of

1h ITF

Interval: 32h 13’

Start:

11.26 GMT 2007/03/08

End:

19.39 GMT 2007/03/09

8-9 March 2007: Opening of new vent Time interval of 11 minutes (11.17-11.28 UT 9 March 2007)

velocity greater than 300 mm/h

0

0,001

0,002

0,003

0,004

0,005

0,006

0,007

0,008

0,009

0,01

09/03/2007

07.12

09/03/2007

07.55

09/03/2007

08.38

09/03/2007

09.21

09/03/2007

10.04

09/03/2007

10.48

09/03/2007

11.31

09/03/2007

12.14

09/03/2007

12.57

09/03/2007

13.40

09/03/2007

14.24

09/03/2007

15.07

inve

rse

of v

eloc

ity 1

/(mm

/h)

vent opening and landslides

Inverse velocity plot 9 March

Thermal camera (750m a.s.l.) on 2007/03/15 20.40 GMT Geophysics Laboratory – Department of Earth Sciences

79

15 March 2007

Explosion

(paroxism)

Sequence of 10’ ITF

Interval: 1h 47’

Start:

18.49 GMT 2007/03/15

End:

20.36 GMT 2007/03/15

SdF velocity in 2007

27 F

eb. e

ffusi

on a

nd la

ndsl

ides

9 M

arch

effu

sion

Crater velocity in 2007

27 F

eb. e

ffusi

on a

nd la

ndsl

ides

15 M

arch

exp

losi

on

RADAR monitoring works in any time/weather condition but spatial resolution is strongly dependent on antenna dimensions and distance

The differential phase contains information on path modification occurred along the LOS between two acquisitions

Needs a coherent radar

Interferometry is possible

The SAR technique allows to collect radar images from large distances with high spatial resolution

Deformation Maps can be obtained

Images acquired in different times can be used if the elapsed time is short compared to surface modifications rate

A surface deformation corresponds to a distance (range) variation

phase is stable in time & space

GB SAR fast acquisition

Conclusions

Conclusions • Ground-based In-SAR technique is used for real-time and early-warning for forecasting eruptions, landslides and related tsunami

• The tecnique permits a costant and continuous monitoring in all weather and environmental conditions

• The inverse velocity method (Fukuzono) is used as model for forecasting the failure time

•  From space the knowledge of the orbital parameters, the

registration of coherent echo, and e.m. fields reconstruction algorithms, make available MW images for RS use.

•  Phase information from pair of images makes available sub-millimetric sensitivity to surface range variations. Great hopes arose on DinSAR from space for: topography (DEM generation), glaciers dynamics, landslides monitoring, subsidence studies

•  ... but in real world accuracy is a little far from expected value: main drawback: revisiting time too long for many applications: temporal decorrelation (repeat pass)

Ground Based DInSAR can offer down to

10 minutes “repeat pass” !

Synthetic Aperture Radar techinque can provide MW images with adequate spatial resolution

Oil spill detection ->

Some SAR images from space

Different areas

<- Flooded areas mapping

To perform it we need: •  spatial/temporal diversity: a motion as the orbit or a linear scan (GB SAR) •  a coherent radar