Synthetic Aperture Radar
Interferometry
Geographical Survey Institute
Government of Japan
Advantages of InSAR
Principle of InSAR
What is SAR (Synthetic Aperture Radar) ？
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Analysis of observation data
in
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n
The SAR image covers tens of kilometers with one observation. Therefore,
we can catch the detailed movement of the ground surface for a wide area.
iv
an
ti
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e
Tr
it
1. Monitoring wide area
ce
SAR is a remote sensing technique
that can image the terrain and its
structure by transmitting a radar
wave from a satellite, etc and
receiving reflection from the
ground.
Satellite,etc
2. No survey equipments required on the ground
The width of “one look” is
The SAR can observe the places where people cannot access
due to a disaster or rugged topography.
10 km ～ 100 km
SAR image
What is InSAR
(Interferometric SAR) ？
SAR data have information of the distance between a
satellite and a ground surface. The deformation on the
ground is detected as a change of the distance.
Interferometric process requires a pair of SAR data acquired
at different times. As a result of the process, we can detect
the deformation on the ground occurred during the period.
The distance to satellite is shorter
than the first observation.
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ve
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rd
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at
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st
Fir
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SAR uses a radar wave, rather than visible light, which can
penetrate the clouds, etc. Therefore, the SAR observation
can be made in day and night under any weather
condition.
ion
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3. All weather observation
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Ob
Japanese SAR satellites
Distance to satellite
u p lift
First SAR image
SAR interferogram based
on the first and second images
Second SAR image
Launch date
Orbital altitude
Total weight
Recurrence cycle
Size of Antenna
Wavelength
Resolution
Off-nadir angle
Scanning width
ground surf ace
How to understand the SAR interferogram
Far
-11.8
Near
-8.9
-5.9
-3,0
0
3.0
5.9
8.9
L O S (l i n e - o f - si gh t) c h a n ge [ c m ]
No deformation
11.8
The SAR interferogram is conventionally expressed
in the change of the colors. When there is no
deformation on the ground surface, the color does
not change. However, when there is any deformation
on the ground surface, the color changes as below.
Gentle changes
c JAXA
Jan. 24, 2006
About 700km
About 4tons
46-day
Width : 3.1m Length : 8.9m
L-band（23.6cm）
7 ∼ 44m
8 ∼ 60°
40 ∼ 70km
Advanced Land Observation Satellite
「ALOS： Daichi 」
「ALOS」and「JERS-1」 adopt L-band sensor that uses
Steep changes
the radar with about 24cm wavelength. This sensor
has a property to penetrate leaves and branches of
c JAXA
（ Feb.1992 - Oct.1998 ）
Japanese Earth Resources Satellite 1
「JERS-1」
trees. Therefore, we can recognize movements of the
ground surface covered largely with plants. The
L-band sensor is effective for an area with forests or
vegetations like in Japan.
Earthquake
Detecting the underground fault movement
Earthquake occurs when the strain accumulated
under the ground is released and the rock slips
along the fault plane.
An inland earthquake occurs at the depth
between a few to twenty kilometers. In that case,
the ground surface around the epicenter is
deformed according to the movement of the fault.
Displacement
on
the ground
Movement
by the fault
under
the ground
Noto Hanto Earthquake
March 25, 2007（M6.9）
10km
Epicenter
m
0c
0cm
From the results of SAR
interferogram and GPS, the
western region of Noto
peninsula moved at most
50cm. The results indicate the
fault model as below.
ne
ult
The active fault on the ground
was not exposed in this
earthquake, because the most
part of the earthquake fault
was under the sea area.
Pla
Fa
m
.2c
47 m
.4c
35 cm
.6
m
23
.8c
11
m
0c
10km
m
.2c
47.4cm
35 .6cm m
23 1.8c
1
Ground surface
1 .2 km
North
0cm
0cm
South
2 1 .2 km
1.65m
Simulated interferogram from
the estimated fault model
Slip Vector
13 . 9km
Far（Subsidence/East）
Fault Plane
SAR interferogram 2007.2 ～ 2007.4 (ALOS)
-11.8 -8.9
-5.9 -3.0
Near（Uplift/West）
0
3.0
5.9
8.9 11.8
LOS (line-of-sight) change [cm]
The estimated fault model
Northern Iwate earthquake
September 3, 1998（M6.2）
This earthquake was
accompanied by the volcanic
activities in Mt. Iwate.
Mt.Iwate
Tazawa Lake
The most remarkable
displacement is located along
the known fault. Moreover,
the deformation pattern on
the ground corresponds to
the topographic features. The
results indicate that the fault
had been activated repeatedly
and formulated the present
topographic feature.
Far（Subsidence/West）
SAR interferogram 1997.11 ～ 1998.9 (JERS-1)
-11.8 -8.8
-5.9 -2.9
Near（Uplift/East）
0
2.9
5.9
LOS (line-of-sight) change [cm]
8.8 11.8
West
East
2D displacement vectors by InSAR
2-dimensional displacement information can
be revealed by combining two InSAR
images observed from different orbit paths.
※　gray ： Topography profiles
※　red arrow ： 2D displacement vectors
By InSAR, we are able to understand the fault system that causes an earthquake, even if the fault
does not reach the surface. To know the fault movement under the ground is important to predict
the occurrence of the aftershocks or simulate the seismic damage from potential earthquakes.
Landslide
Detecting the range of invisible landslide
Landslide is a phenomenon that subsurface layer or mass
on mountainside slides down, triggered by an increase in
groundwater from heavy rains.
When a slope moves greatly by a landslide, it
appears as a "visible" surface deformation like a
collapse of buildings. However, when a slope moves
slightly and slowly, it is sometimes hard to detect the
deformation because it appears as "invisible" one.
Detecting landslide areas
Landslide
The enlarged InSAR image
shows a landslide that
occurred in a mountain region
of Aomori Prefecture.
Shimokita Peninsula
InSAR can catch the "invisible"
and slight surface deformation.
It enables us to assess the area
and risk of a landslide before it
brings us the hazardous
situation.
Towada Lake
Far（Subsidence/West）
-11.8 -8.8
-5.9 -2.9
Near（Uplift/East）
0
2.9
5.9
8.8 11.8
LOS (line-of-sight) change [cm]
SAR interferogram 1992.10 ～ 1998.4 (JERS-1)
The landslide occurred by an earthquake
The left image shows the
ground deformation triggered
by the Noto Hanto Earthquake
in 2007.
Noto Peninsula
1km
Most of the fringes in the
image are deformation caused
by the earthquake, but the
pattern of fringes in circled
areas are different from others.
We concluded these changes
are landslides by considering
the topographical and
geological information.
The red arrow shows the direction of landslide.
Far（Subsidence/East）
-11.8 -8.9
SAR interferogram 2007.2 ～ 2007.4 (ALOS)
-5.9 -3.0
Near（Uplift/West）
0
3.0
5.9
8.9 11.8
LOS (line-of-sight) change [cm]
InSAR can detect an "invisible" and slight surface deformation. Therefore it is effective for discovery
and monitoring of landslides. We can assess the area and risk of landslides with InSAR immediately
after a disaster or in areas that can not be easily accessed.
Volcano
Monitoring underground magma movement
A volcano erupts when magma and/or gas
components are uplifted toward the shallow area.
The mountain
is expanding!
Crustal
Deformation
Maybe erupts!
The body of the mountain inflates as the magma
moves upward and pushes the mountain from
inside. From the crustal deformation detected by
InSAR, we can estimate the volume of the magma
and its movement under the ground.
マグマの昇
Magma
uplift
Magma Chamber
Monitoring volcanoes in domestic area
∼ Io To ( Iwo-jima ) ∼
Io To (Iwo-jima) is the volcanic island in the
Ogasawara Islands. There have been repeated
volcanic activities. Therefore it has been monitoring
by GPS continuously. The GPS graph below shows
Station B has been uplifted greatly with respect to
Station A since Oct. 2006.
8cm
12cm
0cm
4cm
16cm
The left InSAR image shows the crustal
deformation patterns. It reveals the deformation
along the Asodai Fault which cannot be detected
by GPS.
Station B
16cm
（m）
Relative height
0.400
Asodai Fault
GPS Station
8cm
Station A
SAR interferogram
0
km
1
2
0.200
0.000
Observation Period
2006/10/1 ～ 2007/9/1
ift
Upl
-0.200
-0.400
2006/10/01 07/01/01 07/04/01 07/07/01
Height change on GPS station B
(Reference : GPS station A)
2006.11 ～ 2006.12 (ALOS)
SAR interferograms
Contour Interval：2cm
8
0
12
8
4
8
4
-4
4
8
0
-4
12
4
-4
km
0
2006.12 ～ 2007.2
-4
8
4
0
4
0
2
0
2007.2 ～ 2007.4
2007.5 ～ 2007.8
2007.4 ～ 2007.5
The above four InSAR images represent the time-series changes
of the crustal deformation patterns in Io To since Dec. 2006.
These show that the uplift on the east coast is continuing slowly.
Far（Subsidence/West）
-11.8 -8.9
-5.9 -3.0
Near（Uplift/East）
0
3.0
5.9
8.9 11.8
LOS (line-of-sight) change [cm]
InSAR can catch by large-scale monitoring the signal of volcanic activity which has not been
detected so far. SAR is one of the most promising methods for volcano monitoring as it can observe
the unreachable areas by people because of gases and heat from volcanic activity.
Subsidence
Detecting ground subsidence by large-scale monitoring
The cause of subsidence is closely related to human
activities such as excessive groundwater withdrawal
and housing development on soft grounds. As
subsidence affects the structures such as buildings
and roads, monitoring is needed on a regular basis.
The leveling is often used for subsidence
monitoring. It can measure with very high precision,
but only provides us the data at limited numbers of
spots.
Subsidence
Soil
clay layer
Com
of c pact
lay ion
lay
er
gravel layer Groundwater
clay layer
Withdrawal
Com
of c pact
lay ion
lay
er
gravel layer
Soil
clay layer
gravel layer
clay layer
gravel layer
Monitoring subsidence regularly
∼ The T s u g a r u P l a i n ∼
The left three InSAR images
focus on subsidences that
occurred in the Tsugaru Plain,
Aomori Prefecture.
Hirosaki
City
5km
Hirosaki
City
Hirosaki
City
5km
1992.10 ～ 1998.5
(JERS-1)
Far（Subsidence/West）
5km
1995.4 ～ 1998.9
(JERS-1)
Recently the area has not been
monitored by the leveling, but
InSAR shows that subsidence
has been continuing.
2006.4 ～ 2007.4
(ALOS)
Near（Uplift/East）
3.0
-11.8 -8.9 -5.9 -3.0
0
5.9 8.9 11.8 （ALOS）
-8.8
-2.9
2.9
8.8
（JERS-1）
LOS (line-of-sight) change [cm]
ALOS(wavelength:23.6cm) and JERS-1
(wavelength:23.5cm) use L-band. However,
due to the marginal difference in wavelength,
the figure on the ALOS and JERS-1 color bar
are not exactly the same.
SAR interferogram
Example of subsidence
∼ Ariake Sea ∼
Fukuoka Pre.
Omuta-City
The land around Ariake
Sea has been expanded
by reclamation for several
decades.
The left InSAR image
shows us the subsidence
image around Ariake Sea.
SAR interferogram
1993.10 ～ 1996.4 (JERS-1)
This was probably
occurred by the influence
of the great drought in
1994.
Far（Subsidence/West）
-11.8 -8.8
-5.9 -2.9
Near（Uplift/East）
0
2.9
5.9
LOS (line-of-sight) change [cm]
8.8 11.8
Ariake
Sea
SAR interferogram 1993.9 ～ 1993.10 (JERS-1)
The above image represents the
subsidence that occurred in the drained
land along Ariake Sea.
It shows that paddies have subsided
during the rice reaping period due to the
change in the water content of the soil.
InSAR provides the surface deformation patterns of the subsidence in various horizontal scales. It is an
efficient tool for monitoring ground subsidence, as well as detecting an uncharted one.
GSI
InSAR Analysis Project
Domestic area
Ishikari
Precise Ground Deformation
Survey Project
Kushiro
GSI regularly monitors the whole
Tokachi
Tsugaru
nation area and r e l e a s e s t h e s e
results. The information are more
frequently updated especially in
volcanic and subsidence areas.
Niigata
Vo lcano
Sendai
Subsidence area
Fukui
Hiroshima
Kanto
Nobi
Osaka
Shizuoka
(Omaezaki)
Chikugo/Saga
International
cooperation
Asia -Pacific
Crustal Deformation
Monitoring
GSI has been monitoring the
crustal deformation to mitigate
the hazard of natural disaster in
cooperation with countries in
the Asia-Pacific region.
GSI provides InSAR results to
this project.
Original ENVISAT data (c)ESA
Observation Period 17 September ∼ 22 Octorber, 2005
C r us t a l d ef o r m at i o n o c c u rre d b y
t he 2 0 0 5 No r t her n P ak i s t an E ar t h q u ak e .
GSI Geodetic Department, Space Geodesy Division
GSI InSAR Analysis HomePage
Address : 1 Kitasato, Tsukuba, Ibaraki 305-0811, Japan
http://vldb.gsi.go.jp/sokuchi/sar/
TEL : +81-29-864-1111
ALOS and J ER S-1 ra w da ta publish ed in th is pamph let are distributed by ME T I/J A X A .