GA2015 sar monitoring stromboli etc

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Department of Earth Sciences

CENTRE OF COMPETENCE OF THE CIVIL PROTECTION DEPARTMENT PRESIDENCY OF THE COUNCIL OF MINISTERS

Monitoring deformations through Ground-Based radar interferometry N. Casagli, F. Catani, G.Luzi, L. Guerri: Univ. Florence, Earth Sciences Department

D. Tarchi: EU Commission JRC 窶的PSC D. Leva: LisaLab Ltd A JRC spin-off company


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

Ku band

Îťâ‹… f =c


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 The map

A target Radar •

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.


Basic interferometry A wave travels transferring the configuration of a physical parameter (e.m field, sound, a seismic deformation..…) with a velocity c. λ It is characterized by: A amplitude A, wavelength λ, frequency f and phase θ and can generates specific phenomena as: interference and diffraction c= light velocity ~ 3.108 m/s

f=number of cycles per time unit To perform interferometry waves need a stable phase wave

wave

λ⋅ f =c Phase strongly affects waves interaction

interference


Two waves “in phase” yield high intensity Two waves “in quadrature” yield a null intensity In phase

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

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

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

λ ΔR = Δϕ 4π


SAR imaging: the Ground Based approach Azimuth resolution

Pk Rn,k ΔXa (Np step)

n

Azimuth length: L

Azimuth resolution

Main benefits from GB observations:

Range resolution

•  Accurate motion •  Frequency of the observation very high (<hour) •  Zero spatial baseline among images

c 2B λ Δϑ = 2L

ΔR =

B = bandwidth L = scan length λ = wavelength


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

1 I ( Pn ) = n f np

np

2 nk

nf

∑R ∑E k =1

ik e

(

4πf i ( Rnk o )) c

= I (n) e jϕ ( n )

i =1

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


A SAR image is represented through a matrix of complex numbers RADAR

I i ,l = ai ,l e

⎡ 4π ⎤ j ⎢ Ri ,l −Φ noise ⎥ ⎣ λ ⎦

= si ,l e jϕ

2d Amplitude image

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. When a Digital Elevation Model is available we can project the radar image on it 3d Amplitude image


Master Image

M(t , R) = a1i e

−j

λ

R1i

Slave Image

S(t , R) = a2i e

−j

λ

R2 i

*

si = a1,i a2,i e

Topography

B≠0

⎡ 4π ⎤ j ⎢ ( R2 i − R1i ) − Φ noise ,i ) ⎥ ⎣ λ ⎦

= si e jϕ

Displacement

Δφ∝(4π/λ) hr

B~0

B=Baseline

R

Pi Interferometric Phase φ:

φ=arg[MS*] Interferometry provides sub-wavelength sensitivity

Δφ=(4π/λ) ΔR


Interferogram

Phase

*

Time= t0

= Time= t0+Δτ Zero baseline

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

φ = φinstrument al + φscattering + φ geometric + φ atmosferic + φ displacement The amplitude of the conjugate product is related to coherence


Phase wrapping and decorrelation 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


Interferometric Ground-based Imaging Deformeter Linear Synthetic Aperture Radar

InGrID-LiSA

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


Data collection Heliplatform centre Optical cable

Wireless connection

Heli-platform

Radar installation

16


System set-up

17


Ground-based InSAR Continuous-wave stepped-frequency (CW-SF) radar based on a Network Analyser (NWA) operating in the frequency band 17.0-17.1 GHz

target area

Tx

Rx

sled

linear rail 2.8m

source NWA

:

computer

The synthetic aperture is obtained sliding the antennas along a 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 Interferogram (phase difference)

3

Image 2

1

2

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

LOS displacement (mm)

4

phase wrapping

5


Observed scenery February 2003

5

4 3

2 1

Lava flow No.3 Lava flow No.2

Lava flow No.1


Power image HIGH REFLECTIVITY

5 4 3 1 2

LOW REFLECTIVITY SHADOW


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


Lava flows

Feb. 2003

www.ct.ingv.it (Jan 2003)

www.ct.ingv.it (Jan 2003)


Interferogram 12’

LOS displacement (mm)

Lava flow 3 mm in 12’ (15 mm/h)

Interval: 12’ Start: Febr. 21 15:21 End: Febr. 21 15:33


Interferogram 12’

Rapid lava flow (decorrelated)

Interval: 12’ Start: April 1 07:47 End: April 1 07:59


Interferogram 1h

Slope movement (1.5 mm/h)

LOS displacement (mm)

Rapid lava flow

Interval: 1h Start: March 1 07:36 End: March 1 08:36


Interferogram 1h

Slope movement (2.2 mm/h)

LOS displacement (mm)

Rapid lava flow

Interval: 1h Start: April 1 15:00 End: April 1 16:00


Interferogram 1h

LOS displacement (mm)

Slope movements disturbed by lava flows

Interval: 1h Start: April 27 12:05 End: April 27 13:05


Interferogram 1h

LOS displacement (mm)

Slope movements disturbed by lava flows

Interval: 1h Start: December 01 12:05 End: December 01 13:05


Interferogram 1h

Lava flows

LOS displacement (mm)

Slope movement 17 mm in 1h50’ (2.2 mm/h)

Interval: 1h 50’ Start: Febr. 21 19:10 End: Febr. 22 03:02


March 2

δ

α β

February

April, 25

Slope movements on SdF


Slope movements on the crater




Rockfalls inside the crater


Interferogram 12h

Slope movements disturbed by lava flows (phase ambiguity)

Landslides

LOS displacement (mm)

Slope movement (3 mm/ day)

Interval: 12h Start: April 13 01:20 End: April 13 13:20


Interferogram 24h

Slope movements disturbed by lava flows (phase ambiguity)

Diffused landslides

LOS displacement (mm)

Slope movement (3 mm/ day)

Interval: 24h Start: April 11 03:55 End: April 12 13:55


Interferogram 48h Rockfalls

Diffused landslides

Decorrelation due to lava flows

LOS displacement (mm)

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

Interval: 48h Start: March 30 13:45 End: April 01 13:45


Interferogram 75h 07’ Rockfalls

Decorrelation

LOS displacement (mm)

Diffused landslides

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

Interval: 75h 07’ Start: April 26 05:03 End: April 29 08:10


Interferogram 7d 0h 05’ Slope movement (0.9mm/d) LOS displacement (mm)

Decorrelation

Interval: 7 days 05’ Start: December 01 13:54 End: December 08 13:59


Interferogram 12d 9h 45’

Decorrelation

LOS displacement (mm)

Slope movement (phase ambiguity)

Interval: 12 days 09h 45’ Start: April 20 19:16 End: May 05 08:10


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


3m


Before

After


Interferogram across the explosion

LOS displacement (mm)

Decorrelation over all the interferogram

Interval: 1h 52’ Start: April 5 07:52 End: April 5 09:44


Ground-shacking effect


Interferogram after the explosion Slope movement (4 mm/h) LOS displacement (mm)

Slope movement (3.2 mm/h)

Interval: 1h 24’ Start: April 5 09:20 End: April 5 10:44


Explosion SAR sequence Interval: 06’ Phase in degrees

Start: April 5 08:07 End: April 5 08:13


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

27 Feb. 2007 Power images Morphological modifications of the crater and of the upper Sciara del Fuoco Interval: 15h 12’

21.05 GMT

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.

1 α −1

v f = ∞ ⇒ v1i = [A(α − 1)]

if α = 2 then: 1/v = A(tf-t)

Fukuzono (1985)

(t f − t )

1 α −1


ERUPTION AND LANDSLIDES

Inverse velocity plot – 27 February


Landslides of Feb.27


10.57 - 13.37 GMT

LOS displacement (mm)

14.30 - 14.41 GMT

2007/02/27

13.48 - 14.09 GMT

14.41 - 14.52 GMT

71


18.46 - 18.57 GMT

LOS displacement (mm)

cumulated 18.57- 19.29 GMT

2007/02/27

19.08- 19.19 GMT

19.40 -19.51 GMT

72


19.51 - 20.01 GMT

20.44 - 20.55 GMT

20.33 - 20.44 GMT

21.37 - 21.48 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


09/03/2007 15.07

0,002

09/03/2007 14.24

0,003

09/03/2007 13.40

09/03/2007 12.57

09/03/2007 12.14

09/03/2007 11.31

09/03/2007 10.48

09/03/2007 10.04

09/03/2007 09.21

09/03/2007 08.38

09/03/2007 07.55

09/03/2007 07.12

inverse of velocity 1/(mm/h)

Inverse velocity plot 9 March 0,01

0,009

0,008

0,007

0,006

0,005

0,004

vent opening and landslides

0,001

0


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


9 March effusion

27 Feb. effusion and landslides

SdF velocity in 2007


15 March explosion

27 Feb. effusion and landslides

Crater velocity in 2007


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

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

Images acquired in different times can be used if the elapsed time is short compared to surface modifications rate The differential phase contains information on path modification occurred along the LOS between two acquisitions A surface deformation corresponds to a distance (range) variation

Needs a coherent radar

phase is stable in time & space Interferometry is possible

Deformation Maps can be obtained

GB SAR fast acquisition


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 submillimetric 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 Some SAR images from space

Oil spill detection -> <- Flooded areas mapping Different areas

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


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