DETECTION METHOD OF SLOPE FAILURES DUE TO THE 2009 SUMATRA EARTHQUAKE BY USING TERRASAR-X IMAGES...

DETECTION METHOD OF SLOPE FAILURESDUE TO THE 2009 SUMATRA EARTHQUAKE

BY USING TERRASAR-X IMAGES

Toyohashi University of Technology Makoto KAWAMURA

Fukui National College of Technology○Kazuhiko TSUJINO

Fukui National College of Technology Yuji TSUJIKO

Andalas University Jafril TANJUNG

2011 IEEE International Geoscience And Remote Sensing Symposium24-29 July, Vancouver, Canada

Introduction

Debris flow and slope failures typically occur on steep slopes and are often triggered by heavy rainfall or earthquake.In Japan, aerial photographs are usually used for the investigation immediately after the disaster. However, because the aerial photographs are not used for the developing country and a lot of time is necessary to grasp damaged area from the large area.We have proposed the detection method of slope failures by using the optical sensor image in such a situation. However, an optical sensor might not be able to observe the ground by the cloud.On the other hand, because of the SAR image uses the micro wave, the influence of the cloud is not received easily. Therefore, the SAR image can be used for an urgent observation when the disaster occurs.

Target of this study

Motivation

Large Earthquake

To understand

outline

Tounderstand

details

TimeImmediately after the disaster Period of Restoration

Moreover, it is necessary to analyze, while obtained information is a little.

Many InformationAerial photographs

Other satellite imagesField survey

Geological type, terrain ・・・

It is demanded to find the large

damage area, even if there are "miss"

and "wrong extraction".

It is necessary to collect many

information, and analyze damage more in detail.

Three cases were prepared in this research.• Interpretation of the slope failure occurring

by using two time series TSX StripMap images （ color composite image of before and after EQ. ）

• Detection of the slope failures by using TSX StripMap image and local incidence angle.

• InSAR by using TDX images

Methodology

2009 Sumatra Earthquake The 2009 Sumatra

earthquake occurred just off the southern coast of Sumatra, Indonesia.

The major shock hit at 17:16 local time on September 30, 2009 and had a moment magnitude of 7.6.

The epicenter was 45 kilometres west-northwest of Padang, Sumatra.

The situation of Sumatra is similar to the Honsyu (Mainland) in Japan. (Scale, Frequent occurrence zone of EQ. and Received the damage of TSUNAMI.)

The TSUNAMI damage due to the 2004 sumatra earthquake was huge.

Used data in this study

TSX StripMap(VV), Ascending

Feb.8th 2009.(Before EQ)

TSX StripMap(VV), Ascending

Oct. 8th 2009.(After EQ)

TSX StripMap(HH), Descending

Mar. 12nd 2010.(After EQ)

TSX StripMap(HH), Ascending

May 5th 2010. (After EQ)

Geological Map 　West SUMATRA

(1:250,000)Digitized

SPOT-5 image Oct.8th 2009.

SRTM90m-mesh DEM

ASTER GDEM30m-mesh DEM

© CNES 2009

© Infoterra GmbH, Distribution [PASCO]




Azimuth

Range

Azimuth

Range

Azimuth

Range

Azimuth

Range

TamDEM-X (TDX) image

Mar.14 2011 and Mar. 25 2011We requested TDX according to the field survey.

©Infoterra GmbH, Distribution[PASCO]

PadangPadang

Field survey area ： G.TigoField survey

area ： G.Tigo

Field survey

PariamanPariaman

About 50kmAbout 50km

About 20kmAbout 20km

Many building damage occurred in the Padang city.Many slope failures were generated in the mountainous district in the Padang Pariaman Pref.

1st Field survey (Jan. 2010): Measurement concerning shape and size of slope failures2nd Field survey (Mar. 2011): Measurement concerning expansion of slope failures by squall in the rainy season

An example of color composite image


Color composite image of TSX （ R,G,B ） = （ After EQ ， Before EQ ， Before EQ. ）

Comparison of TSX EEC color composite images and field survey result

Backscatter strength is strong at the middle of slope before the earthquake. (Light blue)

Backscatter strength is strong at the main scape after the earthquake.(Red)

Before EQ. After EQ.

Change in geographical features

Main scape

Movement region of soil

Color composite imageField survey©Infoterra GmbH, Distribution[PASCO]

Microwave Microwave

Main scape

• Large scale circular slip• The section of after collapses is

divided into a rapid inclination part and a smoothness part.

• The width of the site A was about 200m.


©CNES 2009

(R,G,B)=(After EQ. ， Before EQ ， Before EQ.)

Field survey (Site A, Jan. 2010）

Site A

Site A （ Mar. 15th, 2011)The dam was constructed in this area.

A part of the accretion sediment was cut out compared with the first investigation, and the unpaved road was constructed.

There was no vegetation in the main scape.


• The width of the center was about 150m.

• The shape of Site B similar to the Site A.

• Rapid inclination slope angle: 26°,• Height is about 35m from the BM.• Smoothness part slope

angle:8°30′ ．• In the top part, there was the tension

crack (about 30cm). ©Infoterra GmbH, Distribution[PASCO]

©CNES 2009

Field survey (Site B, Jan. 2010）

Field survey （ Site B, Mar. 2011 ）

↑ 　 These photographs were ← 　 taken with the RC　　 helicopter. (Bizworks Co.)

• There was a rice field in the south of the site C.

• The width of Site C was abut 100m.• The slope angle of top part from BM

was about 17° ， and Rapid inclination slope angle was about 30° ．


©CNES 2009

Field survey (Site C, Jan. 2010）


Site C (14th Mar. 2011)There was no vegetation in steep slope ．

The main scape had been eroded. Many stripe of erosion by the squall were

able to confirm at the middle of slope.Remarkable growth of the grass was seen

compared with the 1st investigation.→ 　 about 2m over.

Verification data

（ SPOT-5 image （ Spatial resolution: about 10m ）

Slope failure area ：Yellow polygon

Decipherment of the color and field survey results

→Forest area （ Red ） or Sediment （ Loess color ）●Geological type: weathering Tuffs● Combined Large slope failure area about 870,000m2

●Dashed line:G. Tigo 　 districtThree villages were swallowed to sediment at this district.

© CNES 2009

An example of Detection resultsColor composite image of TSX

image and cos(loc)R:1008TSX,G:1008TSX,B:cos(GIM)

Multi-level sliceCase aimed at dark part

Average±1σ1008TSX： 41±21

Cos(GIM)： 0.815687±0.052569

Overlay with verification data○：main scape was able to be detected by the accuracy of 65%.

×：main scape was not able to be detected


Results of InSAR analysis by using TDX pair （ coherence ）

Coherence is high in artificial feature and slope failure area. The feature of x band can be confirmed.


Result of InSAR analysis by using TDX pair

The interference fringe appears in the area where the coherence is high.


Comparison with the SPOT-5 image and InSAR analysis


Site C

Site B

Site A

©CNES 2009

→ Grass grow very quickly in the tropical zone.

Detection accuracy• Because of vegetation area is changed, the detection

accuracy cannot be compared directly. • The detection results were compared with 2nd field survey

result (GPS survey) in March, 2011. • Slope failures were detected by binarize processing of the

coherence image. 　• The GPS tracking was smoothed and the verification data

was made newly.

Site No. Detection

results（ m2）

Verification data

（ m2）

Accuracy(%)

Site A 12280 12500 98

Site B 7400 10600 70

Site C 12300 13300 92

Summary In this research, the detection method of slope failures which used the TSX and TDX images was examined. The conclusions are shown as follows.

• The case of two time series TSX image was used, the main scape was possible to distinguish easily by using color composite image.

• When the TSX image after the earthquake and local incidence angle were used, the main scape was able to be detected by the accuracy of about 65%.

• InSAR analysis was done by using TDX image after the earthquake, and clear interference fringe appeared in slope failure area. Therefore, the InSAR analysis was effective to the detection of slope failures. Detection accuracy was about 70 to 98 %.

Future work• To understand of the volume of slope failure area• DEM of the collapse area is calculated based on the result of

interference fringe.

Acknowledgement

This work was supported by SAR technology and application committee

in 2010 of PASCO Corporation.

Thank you for your attention

DETECTION METHOD OF SLOPE FAILURES DUE TO THE 2009 SUMATRA EARTHQUAKE BY USING TERRASAR-X IMAGES

2011 IEEE International Geoscience And Remote Sensing Symposium24-29 July, Vancouver, Canada

Squall in the rainy season

Detection of expansion

Due to the 2009 Sumatra earthquake

Due to the squall after the earthquake

Plane figure of slope failure

expansion of collapse by squall

DETECTION METHOD OF SLOPE FAILURES DUE TO THE 2009 SUMATRA EARTHQUAKE BY USING TERRASAR-X IMAGES...

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