temporal monitoring of supraglacial lakes on thojo … · alos prism, jan. 2010 we tried to search...

28/July/2011, IGARSS11@Vancouver

TEMPORAL MONITORING OF SUPRAGLACIAL LAKES ON THOJO GLACIER AT BHUTAN

Tsutomu Yamanokuchi (RESTEC), Takeo Tadono (JAXA),

Jiro Komori (NU/JICA), Toru Koike (ESS Co.),

Sachi Kawamoto, Nobuhiro Tomiyama (RESTEC)


What is GLOF?

GLOF (Glacier Lake Outburst Flood) Sudden discharge of large volumes of water from the lake which lie at the end of glacier.

Image form Iwata et. al, E-journal GEO vol.2 (1) 2007

RISK and TRIGGER of GLOF

1) Lake with full of water 2) Occurrence of glacier avalanche,

outbreak of calving ice ,trigger to flooding

3) Increasing vulnerability of moraine dam due to melting of ice core, seepage etc.

Avalanche Landslide

Vulnerability Of Moraine Dam

Glacial Lake

Glacier

Mountainous glaciers has been retreating in this 50years Might have relation with global warming Expansion of glacial lakes

1969

2006


Introduction

• Sudden water outburst event occurred in 29,Apr., 2009 at Tshojo Glacier, Bhutan

• Tshojo Glacier is D-type glacier and has no glacier lake : Strange event…

• Approx. discharged volume is 0.5 million m3 (Komori, 2011)

• However, its water source was not found from ground survey

• Ground survey is quite difficult due to severe geographical condition

Tshojo Glacier 28, Oct., 1986 SPOT-2 / XS


Lower end of glacier was eroded

Tshojo Glacier 2009 GLOF

Field Survey shows…

- Debris flow started from lower part of Tshojo Glacier terminus

- Debris flow blew out from under the surface of glacier

28/July/2011, IGARSS11@Vancouver ALOS PRISM, Jan.

2010

we tried to search the source of the water.

Estimated discharge volume is bigger than hollow and pond.

80 x 90m, dep.20 m

Surrounded by ice

cliff

1.4 km from outlet.

100x100m dep. 20m

Dried up ice tunnel is

exposed

Flooded water come down via these

channel

Field Survey photos

ALOS/PALSAR image told us the source of outflow water!


7, March, 2009 23, July, 2009

View from the space ! • Two ALOS/PALSAR image detected a sudden disappearance event of a

large supra-glacial lake on Tshojo Glacier • The lake seems to be adequate source of the flood. It is necessary to

estimate the volume of this lake and to check the validity of our hypothesis


Objectives

• To investigate the relationship between flood event and disappearance of supraglacial lake through the analysis of time series satellite data

• To estimate the lost water volume of supraglacial lake by ALOS/PRISM DSM

• To validate quantitatively the relationship between water volume of supraglacial lake and increased river water volume estimated from water gauge

• To investigate the similar event trough satellite data analysis


• ALOS/PALSAR (L-band SAR):12scenes

20070302, 20070902, 20080419, 20081020, 20090120, 20090307, 20090723, 20090907, 20091208, 20100123, 20100310, 20110126

• ALOS/AVNIR-2: (Multispectral) 3scenes

20071226, 20100117(Pansharpened), 20101205

• ALOS/PRISM (Panchromatic triplet sensor): 1scene, for DSM extraction after flood

20100117

• SPOT/HRV: 4scenes

20080108, 20090424, 20090519, 20091125

Satellite data Light blue: before flood

Orange : after flood


Preprocessing

• ALOS/PALSAR:

Apply orthorectification and radiometric terrain correction

• ALOS/AVNIR-2:

Use orthorectified data. If PRISM has simultaneous observation, applied pansharpening

• ALOS/PRISM:

Use orthorectified image for pansharpening and DSM

extraction from triplet image

• SPOT/HRV:

Apply orthorectification using SRTM-3 DEM. If PA has simultaneous observation, applied pansharpening


Results: Time series satellite images

20070302 20070902 20071226

20080108 20080419 20081020 20090120 20090307 20090424 20090519 20090723

20090907 20091125 20091208 20100117 20100123 20100310 20101205 20110126

•Lake started to form from Oct., 2008(Yellow circle) •No relation with cyclone Aila •Lake started to re-fill from Dec., 2010 •Due to freezing water, SAR is difficult to interpret •Stable supraglacial lakes exist near here(Red circle)

Cyclo

ne

Aila

Flo

od

eve

nt


20101205

ALOS / AVNIR-2

20090723

ALOS / PALSAR

Results : expanded image around the lake

Start re-filling

20090307

ALOS / PALSAR

20090424

SPOT / HRV

20090519

SPOT / HRV

•Shapes of lake coincided

between SAR and opt.

•Re-filling clearly detected

•Long radius:500m (yellow)

•Short radius:300m (light blue)

•Area size : 117532m2

•Flow velocity is quite slow


Results estimation of water volume from PRISM DSM

Deepest point ：4174m (Yellow star )

Lake surface ：4224m (Red line)

Estimated water volume from ALOS / PRISM DSM : 1464700 m3

Approx 3 times larger than estimation by Komori (500000m3)


Summary and Future plan

Time series satellite data analysis revealed the disappearance of

supraglacial lake occurred after flood event and no relationship with

flood by cyclone Aila. It implies the relationship between flood event

and disappearance of supraglacial lake

Satellite image clearly detected the re-filling of lake water from Dec.,

2010 ALOS / AVNIR-2 image. It is necessary to pay attention to flood

event again

Ellipsoidal height of deepest point and surface of supraglacial lake is

estimated to 4174m and 4224m respectively. Its volume is 1464700 m3

More quantitative research will be necessary through the combined use

of river gauge data and river flow simulation data with satellite data

Supraglacial lake on Juchudake glacier shows similar seasonal change.

We will continue to research the behavior of this lake using ground truth

survey data (This May research survey was held)


Acknowledgements

• This research was supported by JST-JICA, SATREPS project.

• ALOS / PALSAR data were provided by JAXA through the ALOS PI project (PI No. 577)

Thank you very much for your attention!


Acknowledgements

• This research was supported by JST-JICA, SATREPS project.

• ALOS / PALSAR data were provided by JAXA through the ALOS PI project (PI No. 577)

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Variation of area size of lake •SAR image acquired on Jan., 2009 showed less size due to the frozen lake surface water •AVNIR-2 image acquired on Dec. 2010 showed the re-filling of supraglacial lake

temporal monitoring of supraglacial lakes on thojo … · alos prism, jan. 2010 we tried to search...

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