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
Dispensa su applicazioni SAR da terra per monitoraggio deformazioni suolo con particolare riferimento al caso di Stromboli
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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
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