28/July/2011, IGARSS11@VancouverWhat is GLOF? GLOF (Glacier Lake Outburst Flood) Sudden discharge of large volumes of water 1969 from the lake which lie at the end of glacier. Mountainous glaciers has been retreating in this 50years 2006 Might have relation with global warming Expansion of glacial lakes Landslide Avalanche RISK and TRIGGER of GLOFVulnerability 1) Lake with full of waterOf Moraine 2) Occurrence of glacier avalanche,Dam outbreak of calving ice ,trigger to Glacial Lake flooding 3) Increasing vulnerability of moraine dam Glacier due to melting of ice core, seepage etc. Image form Iwata et. al, E-journal GEO vol.2 (1) 2007
28/July/2011, IGARSS11@VancouverIntroduction• 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@VancouverField Survey shows…- Debris flow started from lower part of Tshojo Glacier terminus- Debris flow blew out from under the surface of glacier Tshojo Glacier 2009 GLOF Lower end of glacier was eroded
28/July/2011, IGARSS11@Vancouver ALOS PRISM, Jan.Field Survey photos 2010we 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 Dried up ice tunnel is exposed 1.4 km from outlet. Flooded water come down via these 100x100m dep. 20m channel ALOS/PALSAR image told us the source of outflow water!
28/July/2011, IGARSS11@VancouverView 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 7, March, 2009 23, July, 2009
28/July/2011, IGARSS11@VancouverObjectives• 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@VancouverPreprocessing• 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•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) 20070302 20070902 20071226 Cyclone Aila Flood event 20080108 20080419 20081020 20090120 20090307 20090424 20090519 20090723 20090907 20091125 20091208 20100117 20100123 20100310 20101205 20110126
28/July/2011, IGARSS11@VancouverResults : expanded image around the lake ALOS / PALSAR 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 20090307 20090424 SPOT / HRV ALOS / PALSAR ALOS / AVNIR-2 20090519 20090723 20101205 Start re-filling
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 planTime 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 lakeSatellite 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 againEllipsoidal height of deepest point and surface of supraglacial lake is estimated to 4174m and 4224m respectively. Its volume is 1464700 m3More quantitative research will be necessary through the combined use of river gauge data and river flow simulation data with satellite dataSupraglacial 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@VancouverAcknowledgements • 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) 125000 120000Variation of area size of lake 115000•SAR image acquired on Jan., 2009 110000 105000showed less size due to the frozen 100000lake surface water 95000•AVNIR-2 image acquired on Dec. 900002010 showed the re-filling of 85000supraglacial lake 80000 2009/04 2010/12 2008/10 2009/01 2009/03 0.5