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Long-term subsidence monitoring of city areas at Nordic latitudes using ERS SAR data: preliminary results

Tom Rune Lauknes(1) and Torbjørn Eltoft(2)

(1) NORUT Information Technology Ltd., Tromsø Science Park, N-9291 Tromsø, Norway
(2) University of Tromsø, Department of Physics, University of Tromsø, N-9037 Tromsø, Norway

Abstract

Differential SAR Interferometry allows us to determine ground displacements with centimetre level accuracy. This poster will present results by using the new Small Baseline (SB) algorithm for long-time surface deformation monitoring.

The SB technique is based on a combination of differential SAR interferograms characterized by a small orbital baseline. This limits the spatial decorrelation. Using the singular value decomposition method makes it possible to "link" independent SAR datasets, separated by large baselines. This increases the temporal sampling rate. The spatial and temporal information makes it possible to identify and compensate for the atmospheric phase artifacts. The SB algorithm also includes an estimate of the topography error given possible errors in the reference DEM.

The test area is the urban area of Oslo, Norway, where there has been a lot of tunnel construction work during the past 10 years. This has caused subsidence of several centimeters at different locations, which are documented by land surveillance techniques carried out in conjunction with the tunnel construction work.

For this ESA AO project a total of 41 scenes from the European Remote Sensing Satellites ERS-1 and ERS-2 covering a time interval from May 25, 1992 to February 17, 2000 has been acquired on a descending orbit (track 337 and frame 2394). Out of these scenes, 11 are from the winter, and 30 from the spring-autumn period. We have 18 scenes from the ERS Tandem geometry. The baselines span a wide range giving different subsets. The raw data sets are processed to single-look-complex SAR images using the Extended Exact Transfer Function (EETF) developed at FFI. The interferometric SAR processing and geocoding is done with software developed at NORUT IT. The topographic phase contribution is being removed by a reference DEM. We are using SNAPHU for phase unwrapping. The SB technique is applied as a post-processing step to the set of differential SAR interferograms generated. Finally, the temporal differential InSAR phase is analyzed in conjunction with the ground measurements.

 

Workshop presentation

Full paper

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry