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|Title||Mapping creeping landforms in Alpine periglacial environment using TSX archives (Western Swiss Alps, Switzerland) – LAN1145 Extension|
|Investigator||Barboux, Chloé - University of Fribourg, Department of Geosciences, Geography|
The project aims at both updating and upgrading the creeping landform inventory in the Western Swiss Alps using TSX stripmap mode interferometric data (single polarization, 3m resolution, 30 km swath width, 11 days acquisition time interval). It concentrates on areas situated above the tree line, which is mainly located in the Alpine periglacial belt. The existing inventory is essentially based on manual interpretation of a large set of C- and L-band DInSAR data from the 1990s and needs to be renewed (1,2,3).
Specific objectives of the proposed activity include:
The previous studies have shown that a large set of SAR scenes covering several years and various time intervals was necessary to establish inventories of slope motion in a confident way (1-4). It is thus expected that the use of a TSX dataset as large as possible will surely increase the relevance of these existing inventories by allowing a more accurate detection of moving landforms and a better quantification of their displacement rate in many cases. Attempts to develop automated methods for the detection of slope movements also show the need of large TSX dataset (5). Finally, we would like to suggest the potential use of this kind of complete set of repeated acquisitions for detecting a change (automatically?) in the deformation rate of active landforms moving with a velocity rate in the order of cm/month to dm/month.
The innovative character of this project was to investigate automated techniques to detect and map slope movements in Alpine periglacial environment. The objective of this project was to - so far as possible - automatically update existing inventories of slope movements of Western Swiss Alps by integrating the most recent DInSAR data in order to detect potential change in activity rate of landforms (1). The current inventory indicates the outlines of moving zones through detected signals of different magnitude orders (cm/day, dm/month, cm/month, cm/year). It contains signal patterns that are related to different phenomena like glaciers, debris-covered glaciers, push-moraines, active rock glaciers, landslides and saggings. In order to obtain new information of active rock glaciers and moving landslides in the studied area, the plan was to use a large set of TSX SAR data (2008-2013).
This project proposes a semi-automated method to map the slope movements in the Alpine environment from TSX interferometric phase and coherence images. The resulting map of slope movements provides a general overview of the surface deformation occurring over the area during a specific time interval (2-4).
Finally, when using a defined set of parameters, the proposed procedure performs automatically the detection and mapping of DInSAR signal.
1) Rough estimation of deformation rate
2) Update of existing inventories
The automatic rough estimation of deformation rate was used in a small studied area using large set of TSX DInSAR scenes from summers 2008 to 2012 in order to update past moving slope inventories (2-4, fig.3). The method was evaluated by analyzing the accuracy to detect a change in deformation rate of DInSAR polygons. False change detection is mainly due to external factors as vegetation, snow or atmosphere (where the signal is noisy), due to border effect in layover and shadow areas, as well as due to a change of the outline of the landform.
3) Upgrade of existing inventories
4) Monitoring of slope movements
Finally, this project has shown that it is possible to develop automated methods for the detection and the mapping of slope movements in an Alpine environment. The proposed procedure delivers maps providing a general overview of the surface deformation occurring over the area during a specific time interval. These mapping of slope movements can be used to update automatically the existing inventories of DInSAR polygons. However, experiments show that manual upgrade is maybe the most reliable technique and that these maps are all the same useful to help expert as a visual tool for the interpretation of surface deformation and by reducing the subjectivity. We also suggest an additional use of these maps, much more local, allowing the survey of specific landforms in term of changing activity.
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