Abstract
Abstract. In this study we investigate stability of Lake Urmia bridge, locally also known as Shahid Kalantari’s highway bridge, in northwest of Iran using high-resolution satellite radar imagery. The radar dataset includes 22 SAR images acquired in SpotLight mode from 2014 to 2015 in an ascending orbit by TerraSAR-X satellite. A high-resolution Digital Elevation Model (DEM) of the area was constructed from a pair of TanDEM-X bi-static data on June 2012 to remove the effect of topography from interferometry observations. The analysis of X-band interferograms shows high number of displacement fringes, which are interpreted as being caused by thermal dilation due to temperature differences in the imaged area between two SAR acquisitions. This effect, which can often be observed in single interferograms, have important impact on time-series products and should be considered for deformation analysis of bridge structures.
Highlights
Geodetic monitoring of bridges is important for evaluating structural conditions and helps avoid human or financial losses caused by early fatigue in the structure
The smoothest TDX Digital Elevation Model (DEM) along the causeway is obtained from National Cartographic Centre (NCC) topographic model and it has the lowest variance value as compared to other products
As seen the TDX DEM produced by NCC has an absolute accuracy three times better than TDX based on SRTM-X and four times better than TDX based on SRTM-C on the bridge
Summary
Geodetic monitoring of bridges is important for evaluating structural conditions and helps avoid human or financial losses caused by early fatigue in the structure. The bridge has a total length of about 1.7 km and consists of 4 different parts with symmetric geometrical structures including approach, transition, viaduct and arch bridge in its eastern and western parts. Previous studies using Envisat, ALOS and TerraSAR-X data show that two embankments on the eastern and western side of the bridge are subject to subsidence with rates exceeding. To that a term which is related to temperature is added to the model which computes three unknown parameters for each edge in Delaunay triangulation between PS points: ek. We show how phase differences caused by thermal dilation can influence deformation maps derived from small baseline interferograms
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