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Summary of Proposal HYD0562

TitleGLOF Glacial Lake Mapping
Investigator Wiesmann, Andreas - GAMMA Remote Sensing AG, N/A
Team Member
Dr. Strozzi, Tazio - GAMMA, N/A
Prof. Kääb, Andreas - University of Oslo, Department of Geosciences
Wegmüller, Urs - Gamma Remote Sensing,
Santorio, Maurizio - Gamma Remote Sensing,
Werner, Charles - Gamma Remote Sensing,
SummaryThis proposal is in support of the ESA DUE INOVVATOR 2 project GLOF, Glacial Lake Mapping. The global climatic change during the first half of the twentieth century has brought a tremendous impact on the high mountainous glacial environment. Many of the big glaciers melted rapidly and gave birth to a large number of glacier lakes forming between the glacier and the end moraine. Due to the faster rate of ice and snow melting, the accumulation of water in these lakes has increased rapidly and resulted in sudden discharge of large volumes of water and debris and flooding in the downstream. The change of mass balance due to the retreat can also affect the slope stability of the surrounding area. Collapsing slopes can also lead to a (temporal) dam blocking the water runoff and leading to a temporary lake. Glacial lake outburst floods (GLOF) causes disasters to life and property along the downstream, result in serious death tolls and destruction of valuable forests, farmlands and costly mountain infrastructure. It has to be mentioned that glacial lakes are not only of interest for hazard prevention but more general for water resources management. The project shall address the end-users need for information on the spatio-temporal behavior of a specific glacial lake or the localization and mapping of lakes over a wider area. To be independent of weather conditions and daylight, radar data is favorized for the identification and mapping of glacial lakes, namely very high resolution SAR data from Terrasar-X. The motivation for this project is the immediate need for glacier lake information by FOCUS and ICIMOD and others. FOCUS is a humanitarian aid company helping to build capacity in Tajikistan also for hazard and risk management and prevention. Among them are hazards related to glacial lake outburst floods (GLOFs). The International Centre for Integrated Mountain Development (ICIMOD) stress the strong need for reliable glacial lake mapping with respect to GLOFs. ICIMOD conducted a study entitled “Inventory of glaciers, glacial lakes and glacial lake outburst floods and monitoring and early warning systems in Nepal and Bhutan” from June 1999 to March 2002 (e.g. Mool et al. 2001). The project prepared spatial database on the glaciers and glacial lakes of Nepal and Bhutan with the application of optical remote sensing (RS) and geographic information systems (GIS). The main purpose of the study was to assess the threat from glacial lakes and to highlight those where GLOF events are likely to occur and cause serious damage to human life and property. In continuation, similar studies in other parts of Hindukush - Himalaya were conducted, namely in selected basins of India, China and Pakistan. The outcome of all these investigations stresses the need for a hazard warning system based on remote sensing and GIS. In spring 2002, the United Nations Environment Programme (UNEP), launched a high-level warning in view of the dramatic growth of gigantic glacier lakes in the Himalayas. The international working group on “glacier and permafrost hazards in mountains” (GAPHAZ) by the International Association for the Cryospheric Sciences (IACS) and the International Permafrost Association (IPA), which involves a large number of potential end- users, identifies glacier lakes as one of the most pressing threats related to surface and sub-surface ice in mountains. With the proposed project we address these needs and extend the capacity of the users by providing technology so far not available to the users by conducting a series of demonstration cases in response to specific end-user requirements.
Final ReportGlacial lake detection has to address the spatio-temporal behaviour of lakes, including appearance, disappearance and growing of known or unknown lakes threatening the population downstream. Glacial lake development to a dangerous level often occurs over years and optical remote sensing analysis is a useful tool to assess these potential hazards. But the development of glacial lakes may also happen within days or weeks (e.g. Narama et al., 2010), posing special challenges to frequent and area-wide monitoring. SAR sensors may be in particular useful, or in some regions even the only monitoring means, for such rapidly-developing lakes where the availability of cloud-free optical data is severely limited. In addition, satellite SAR acquisitions can be programmed well in advance and their use in rigorous planned surveying activities is assured independently of the weather providing a good timeliness of the data. We reported on the use of very high resolution satellite SAR data for reliable and robust glacial lake mapping. During the data interpretation, confusion with wet snow and wet sand areas has to be taken into account because of the very low backscattering intensity similar to that of water. Zones of icebergs and ice debris floating on the lakes, in particular at calving fronts, are confused with land if the interpretation is based on backscatter intensity only. In many cases, though not necessarily in all, multi-temporal analyses might hint to this type of misclassification. In addition, it is important to notice that ascending and descending orbits have different viewing geometries, especially into steep valleys, leading to different hidden areas. DEM quality and availability is crucial. We found that for the general use, SRTM4 proved to be the best large scale DEM available, but did not yet incorporate the ASTER GDEM version 2 in our tests. Visualisation of the data in Google Earth showed localisation errors between our SRTM4-based orthorectification with the Google Earth Landsat images of about 10 to 50 m. A drawback in the visual interpretation of satellite images applied in this study, 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 with SAR data is shadow or layover of the lake’s shorelines. But up to a 1 : 10 000 scale the produced outlines fit well with the in-situ validation data. Costs and processing effort of satellite SAR data are similar to that of satellite optical data, although interpretation, as explained before, might need more training. Thus, we envisage that the provided service is mature and complements well the more established optical remote sensing technology (Schneider, 2004; Ka¨ab et ¨ al., 2005a; Quincey et al., 2005; Ukita et al., 2011; Mergili et al., 2012). The users involved in our study are developing more capacity in radar remote sensing analysis as part of ongoing and future risk management interventions in Tajikistan and the Himalayas. The huge archive of satellite SAR data dating back to the nineties allows for reconstruction of large lake historical data over the last 20 yr, and the high observation frequency with several commercial very high resolution sensors, in particular TerraSAR-X, permits short reaction time to monitor rapid changes in all affected areas on the globe. With the upcoming Sentinel-1 satellites (Snoeij et al., 2011), additional SAR sensors will become available for monitoring the earth at very high temporal frequency.

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