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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)
28/July/2011, IGARSS11@Vancouver
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
28/July/2011, IGARSS11@Vancouver
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
28/July/2011, IGARSS11@Vancouver
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!
28/July/2011, IGARSS11@Vancouver
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
28/July/2011, IGARSS11@Vancouver
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
28/July/2011, IGARSS11@Vancouver
• 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
28/July/2011, IGARSS11@Vancouver
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
28/July/2011, IGARSS11@Vancouver
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
28/July/2011, IGARSS11@Vancouver
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
28/July/2011, IGARSS11@Vancouver
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)
28/July/2011, IGARSS11@Vancouver
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)
28/July/2011, IGARSS11@Vancouver
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!
28/July/2011, IGARSS11@Vancouver
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)
80000
85000
90000
95000
100000
105000
110000
115000
120000
125000
0.5
20
08
/10
20
10
/12
20
09
/01
20
09
/03
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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
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