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Glacial Lake Mapping with Very High Resolution Space-borne SAR
 

Glacial Lake Mapping with Very High Resolution Space-borne SAR

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Glacial Lake Mapping with Very High Resolution Space-borne SAR

Glacial Lake Mapping with Very High Resolution Space-borne SAR

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    Glacial Lake Mapping with Very High Resolution Space-borne SAR Glacial Lake Mapping with Very High Resolution Space-borne SAR Presentation Transcript

    • Glacial Lake Mapping with very High Resolution Space-borne SAR Andreas Wiesmann 1 , Tazio Strozzi 1 , Andreas Kääb 2 1 GAMMA Remote Sensing AG, Switzerland 2 Dep. Geoscience University of Oslo, Norway
    • ESA DUE GLOF (ESRIN 22140/08/I-EC) Objectives and Scope of the Project
      • Provide a service that addresses the need for information on glacial lakes, glacial lake extent and glacial lake extent change, with respect to GLOF based on very high resolution SAR
      • The resulting information will be in a form that it can be easy integrated in the end-users GIS systems and used within the available infrastructure.
      • Why Very High Resolution SAR?
        • Very High Resolution SAR has 2m spatial resolution
        • Many operating systems with ~11 day repeat pass
        • Independent of weather and daylight
    • Introduction
      • GLOF: Glacial lake outburst floods
      • Central and Southeast Asia, the Andes of South America, and those countries in Europe that have glaciers in the Alps have been identified as the regions at greatest related risk
      • Large and inaccessible areas e.g. in the Pamir and Himalayan mountains, cannot be easily supervised; therefore, remote sensing data are an important information source to gather information on glacial hazards in these areas
      • The main problem of optical remote sensing is cloud cover
      • High and very high resolution SAR data may be valuable complementary information sources
    • GLOF in the context of High Alpine Risks Lake Blockage - Dam - Moraine - Landslide - Topography Glacier - runoff - melt - change Timely Occurance Spatially Event - Glacier ice breakoff - Dam break - Landslide - Mass balance change Hazard Change
    • ESA DUE GLOF (ESRIN 22140/08/I-EC) Users
    • User Requirements
    • Product Description
      • Classification between water, ice and others
      • Manual mapping and interpretation of satellite radar images
      • Lake outlines and possibly glacier outlines are delivered in the requested projection as shape files at 10 m resolution for easy integration into GIS applications
      • Supplementary geotiff’s of the geocoded SAR images with a layover and shadow mask
      • The geometric accuracy of the glacier lake maps depends, a part from the data source, to the posting of the DEM available for geocoding
      • Service Implementation is mainly based on new acquisitions, but historical ERS, ENVISAT and ALOS SAR images were also considered
    • Potential hazardous glacier lakes in CH
    • Glacier lake mapping with TerraSAR-X
    • DEMs for terrain-corrected geocoding Use SRTM4 for terrain-corrected geocoding of satellite SAR images if any other high-quality DEM (e.g. ~30 m posting and  3 m vertical accuracy) derived from 1:25’000 topographic maps is not available
    • Area of interest in Nepal
    • Satellite SAR Data in Nepal
    • Glacier lake mapping with TerraSAR-X 07.05.2003 21.02.2005
    • Glacier lake mapping with TerraSAR-X 21.02.2005 03.03.2004
    • Imja Tsho lake ERS-1/2 SAR May 1992 ERS-1/2 SAR Apr. 1996 ERS-1/2 SAR Jul. 2001 TerraSAR-X Apr. 2009 TerraSAR-X Oct. 2009 Google Earth May 2003 ALOS PALSAR Nov. 2007 ALOS PALSAR May 2008 ALOS PALSAR Nov. 2009
    • Lower Barun lake ERS-1/2 SAR May 1992 ERS-1/2 SAR Apr. 1996 ERS-1/2 SAR Jul. 2001 TerraSAR-X Apr. 2009 TerraSAR-X Oct. 2009 Google Earth Mar. 2004 ALOS PALSAR Nov. 2007 ALOS PALSAR May 2008 ALOS PALSAR Nov. 2009
    • Lumding Tsho lake ERS-1/2 SAR May 1992 ERS-1/2 SAR Apr. 1996 ERS-1/2 SAR Jul. 2001 TerraSAR-X Apr. 2009 TerraSAR-X Oct. 2009 Google Earth Feb. 2005 ALOS PALSAR Nov. 2007 ALOS PALSAR May 2008 ALOS PALSAR Nov. 2009
    • Tsho Rolpa lake ERS-1/2 SAR May 1992 ERS-1/2 SAR Apr. 1996 ERS-1/2 SAR Jul. 2001 TerraSAR-X Apr. 2009 TerraSAR-X Oct. 2009 Google Earth Feb. 2005 ALOS PALSAR Nov. 2007 ALOS PALSAR May 2008 ALOS PALSAR Nov. 2009
    • Validation
      • The fluctuation of the water level in winter and summer is around 1 to 2 m so that the shoreline of the lakes may vary up to 20 m (1-2 pixels); for monitoring of changes in shorelines, pixel sizes less than 10 m will be required
      • In some of the images the calving of floating icebergs is not considered as lake
      • A drawback in the visual interpretation of satellite images compared to automated methods is that the area of the lake may vary according to personal subjective interpretations
      • Another aspect which should be considered in the shoreline mapping is the shadow or layover of the lake’s shorelines
    • Imja Tsho lake TerraSAR-X Apr. 2009 Field survey May 2009 TerraSAR-X Oct. 2009
    • FOCUS requirements (based on BOKU work TajHaz)
    • Satellite SAR Data in Tajikistan
    • Glacier lake mapping in Tajikistan
    • Glacier lake mapping in Tajikistan
    • Conclusions: Glacier lake mapping with very high resolution SAR
      • In general, the identification of glacier lakes and their mapping was found to be straightforward for TerraSAR-X based on low backscattering intensity
      • With respect to Google Earth the TerraSAR-X derived shape files have varying offsets of about 50 m
      • Accurate mapping of the glacier outlines from the backscattering intensity is not possible
      • In all these images areas in layover or shadow are masked in black and should be not confused with lakes
    • Conclusions: Glacier lake mapping high resolution SAR
      • On the larger lakes the performance of ENVISAT ASAR data is similar to that of TerraSAR-X and temporal changes of the lake area can be noticed from the ALOS PALSAR images
      • Smaller lakes cannot be reliably detected using Envisat ASAR
      • The performance of ERS-1/2 SAR data is similar to that of ENVISAT ASAR because these two sensors have similar ground resolution and operate at the same frequency
      • With ALOS PALSAR data the distinction of the glacier lakes seems to be less problematic than with ENVISAT ASAR data, however, the problems with the small lakes persist due to the spatial resolution of 10-20m.
    • Future: Glacier lakes within high mountain risks
      • Lake detection has to address the spatial/temporal behavior of lakes, including appearance and disappearance of known or unknown lakes. Glacier lake development to a dangerous level often occurs over years, but may also happen within days or weeks. SAR sensors may be in particular useful or in some regions even the only monitoring means for such rapidly-developing lakes, where time for finding cloud-free optical data is severely limited.
      • GLOF is a process that involves glacier lakes as the major source of water but is usually part of a chain reaction, both before and after the lake outburst itself. GLOF has therefore to be understood as an integrative part of (sometimes dangerous) high-mountain processes around the lake of concern.