results of landslide detection based on insar...

Baota landslide in ChinaThe Baota landslide, located in the middle of theThree Gorges Reservoir, upstream of Dam site223km, downstream of Chongqing 388km and sitedon the left bank of the Yangtze river. A GPS andterrestrial network was established and measuredthree times. This geodetical data set was used forthe validation of the InSAR results.

The choosen approach consists of several levels ofSAR data processing of the European RemoteSensing satellites ERS 1 and 2. At the beginning ofthe processing levels we used the subsampled 3sec-SRTM Digital Elevation Model (DEM) instead to ourstandard approach of using data of the ERS1/2tandem mission for the DEM determination, becauseit turned out that we got more precise results. ThisDEM serves on the one hand as a necessaryprocessing level for the further SAR processing andon the other hand as an important data source forthe GIS in the alert system, e.g. for the derivation ofslope parameters.

The further processing levels were based on thedifferential interferometry approach using two or morecoherent ERS 1 and 2 radar scenes for the finalinterferogram calculation. The different steps, likecoregistration, filtering procedures, unwrapping, etc.were accompained by taking manual correctiveactions, because the existence of two vegetationperiods and the steepness of the terrain in this areawere not the best boundary conditions for InSARprocessing.

The displacements on the Baota landslide of up to14mm in six months from the InSAR processing werein extremely good coincidence with the geodeticderived movement rates.

Results of landslide detectionbased on InSAR processing

Björn Riedel1 and Kostas Lakakis2

The use of differential Synthetic Aperture RadarInterferometry (dInSAR) for the detection andmonitoring of earth surface processes is meanwhilean established method. However, this approach hasonly success if the observed area fulfils specificrequests, like sufficient backscattering, flat slopegradients or very slow growth of vegetation.

In the European Union funded project OASYS -integrated optimization of landslide alert systems –the early identification of endangered areas playsthe main important role (www.vce.at/oasys). For therecognition of surface movements one has decidedto investigate the capability of dInSAR. Within theframework of this EU-project several test sites i.e. inGreece, Germany, Hungary, Rumania and Chinawere investigated. Our InSAR investigations wereespecially focused on the Baota landslide in Chinaand the Prinotopa landslides in Greece.

•satellites: ERS1 & ERS2•image pair: 23424_06256•January – July 1996•baseline Bperp ≈ 23 m•precise ephemeris

Contact address:1Technische Universität BraunschweigInstitut für Geodäsie und PhotogrammetrieGaußstraße 2238106 BraunschweigGermanyb.riedel@tu-bs.de

•SRTM 3”- DEM dataset overlayed onamplitude image•Colour cycle change inheight of 500m

Baota landslide

Changjiang (Yangtze river)

max. movement rates in lineof sight of 14mm in 6 months

Prinotopa landslides in GreeceThe test site is located in NW Greece in the provinceIoannina and the new constructed Egnatia Motorwaywill pass this area. For the detection of landslides weused amodified 3pass-Interferometry (baselines of 12 to 26m),consisting out of one ERS1/2-Tandem data set(January 1996) and an ERS2 image acquisition in April1996 and Mai 1996.

With an overlay of the two 3pass-results we got several identical clusters of pixels that showed usa change in colour in relation to their vicininty.

These areas of earth surface changes of 2 up to 4cmare in good correlation with geological studies andgeodetical on-site observations.

Prinotopa landslide area

2Egnatia Odos S.A. 6o KmThessaloniki-ThermiP.O 57001ThessalonikiGreeceklakakis@egnatia.gr