Hugo Raetzo

Interpretation of Aerial Photographs and Satellite SAR Interferometry for the Inventory of Landslides

An inventory of landslides with an indication of the state of activity is necessary in order to establish hazard maps. We combine interpretation of aerial photographs and information on surface displacement from satellite Synthetic Aperture Radar (SAR) interferometry for mapping landslides and intensity classification. Sketch maps of landslides distinguished by typology and depth, including geomorphological features, are compiled by stereoscopic photo-interpretation. Results achieved with differential SAR interferometry (InSAR) and Persistent Scatterer Interferometry (PSI) are used to estimate the state of activity of landslides around villages and in sparsely vegetated areas with numerous exposed rocks. For validation and possible extension of the inventory around vegetated areas, where InSAR and PSI failed to retrieve displacement information, traditional monitoring data such as topographic measurements and GPS are considered. Our results, covering extensive areas, are a valuable contribution towards the analysis of landslide hazards in areas where traditional monitoring techniques are sparse or unavailable. In this contribution we discuss our methodology for a study area around the deep-seated landslide in Osco in southern Switzerland.

Survey of landslide activity and rockglaciers movement in the Swiss Alps with TerraSAR-X

Four TerraSAR-X stripmap mode scenes acquired during the late summer of 2008 in the Oberwallis region in the Swiss Alps have been interferometrically analyzed for the survey of the activity of unstable slopes. Differential interferometry was applied using a high precision external Digital Elevation Model (DEM). Position, extent, contour, and approximate velocity of unstable slopes were determined for a large area. Selected results representing rockglacier movement and landslide activity are discussed and compared with in-situ information and interferograms derived from ENVISAT ASAR, JERS-1 SAR and ALOS PASLSAR data. This application strongly benefits from the higher spatial resolution of the TerraSAR-X data in comparison to the C- and L-band sensors used in the past, because many of the instabilities are of relatively small size.

Satellite and Terrestrial Radar Interferometry for the Measurement of Slope Deformation

Synergistic use of satellite and terrestrial radar interferometry was considered for the measurement of slope deformation in the Mattervalley (Canton of Valais, Switzerland). Highest rates of movement of more than 1 cm/day were measured only with terrestrial radar interferometry, because of the large time interval between satellite SAR observations. Summer TerraSAR-X and Cosmo-SkyMed interferograms as well as terrestrial radar interferometry campaigns repeated with a time interval of a few days were jointly considered for the study of landslides moving at rates of dm/year. Persistent scatterer interferometric analyses conducted with ERS-1/2, ENVISAT, Radarsat-2, TerraSAR-X and Cosmo-SkyMed images were finally used to detect the slowest moving landslides, with rates of movement below a few cm/yr in the line-of-sight direction.

Monitoring active rock glaciers in the Western Swiss Alps: Challenges of Differential Sar Interferometry and solutions to estimate annual and seasonal displacement rates

This paper describes a new method to monitor active rock glaciers using DInSAR technique with Terrasar-X data acquired with mode facing slope and 11 days time interval during late summers 2009 to 2011. Where the spatial distribution of the rock glacier surface deformation derived from the DInSAR data using conventional unwrapping processes fails due to the relative small size and the complex movement of some rock glaciers, a specific profile is here defined through the rock glacier and is used to analyze the DInSAR products along it. Firstly, the prerequisites to perform such analysis at local scale are given. Then a quantification and discussion of results are achieved through different examples of active rock glaciers encountered in Western Swiss Alps.

Landslide mapping in Switzerland with ENVISAT ASAR

In the frame of the IGARSS 2012 special session on ENVISAT the landslide mapping activities in Switzerland using ENVISAT ASAR data are presented. Between 2005 and 2010 the building up of a well suited archive over the Swiss Alps was realized through programming of all IS2 mode data during the snow free period. In recent years DINSAR and PSI based landslide inventory and monitoring products started to play an important role in the updating of hazard maps.