Science Service System

Summary of Proposal LAN2379

TitleMonitoring of Lochkov bridge by Persistent Scatterers Interferometry
Investigator Sustera, Jiri - Gisat, Sales and marketing department
Team Members
Mgr. Kolomaznik, Jan - GISAT s.r.o., Department of Remote Sensing
Ing. Sustera, Jiri - GISAT s.r.o., Department of Remote Sensing
PhD Hlavacova, Ivana - Czech Technical University in Prague, Faculty of Civil Engeneering, Department of Geomatics
SummaryThe aim of the project is to estimate magnitude and velocity of deformations of Lochkov highway bridge, Prague, Czech Republic. Results should provide synoptic view of deformations and the bridge behaviour in time, which would support decision making of responsible authorities and organisations. Demonstration should contribute to adoption of innovative EO data and services in transportation infrastructure monitoring domain in the Czech Republic. Methodology shall be based upon persistent scatterers interferometry technique with thermal expansion correction. Due to size, character and magnitude of anticipated deformations of the bridge construction an acquisition of one-year-long TerraSAR-X Starring SpotLight mode data series from ascending track is requested. Deliverables shall comprise both graphical and tabular materials showing resulting identified deformations, presentations and summary report.
Detailed report* AOI description * Radotín bridge connects two frequent highways from Prague and is located above the confluence of Vltava and Berounka rivers. It is built as two different bridges from steel and concrete, measuring 236 m (one segment) and 2045 m (4 segments, with a unique construction based on oblique pillars). Shortly after putting into operation, in September 2010, microscopic cracks in welding of metal supports emerged. The fissure has been monitored conventionally – as a unique addition, it has been expected that InSAR techniques can bring a complex view at the bridge behaviour and indicate its potential deflection. * Satellite and ancillary Data * For the area, 33 TerraSAR-X Staring SpotLight scenes were acquired with temporal resolution of 11 days within one year period (Jun/2014 - Jun/2015). LOS sensitivity to the temporal dilation is sh,long = 49% for this configuration while for vertical movements, sv = 85%. Further ancillary data were obtained: - Thermal measurements for day/hour of image acquisition (10 minutes frequency) from nearest meteorological station (large set of thermal and weather variables) (Czech Hydrometeorology Institute) - Thermal measurements from detector located on adjacent segment of bridge (Road and Highway Directorate) - Detailed digital surface model from lidar (Czech cadastral survey) * Processing* SARproZ(c) software was utilized form MTI processing. Advantage is possibility to include thermal component into the processing chain. Precise DSM was utilized for correction of height estimates. Deformation areas above rivers were detected. At both directions from these areas decrease in coherence was investigated, therefore processing had to be carried out independently for eastern and for western part of the AOI (bridge). It is expected that decrease of coherence would not be so high in case of processing of longer time series of InSAR data. MTI processing was divided into 2 parts: 1) preliminary processing of 8-month data stack 2) final processing of full 12-month data stack Based on preliminary results, potential issues were encountered related to thermal dilatation component and correlation between estimated deformation signal and thermal dilatation. Based on that, adaptation of processing chain was conducted. Experience from other parallel projects focusing on bridge deformation monitoring were discussed and crosschecked (LAN1130, LAND2833). * Results * The correlation between estimated deformation signal and thermal dilation is weaker than in the previous processing of only 8-month data , but it still remains. There was a motion detected for points with significant thermal dilatation component on the bridge at current PS InSAR results. This may, however, had been related to only one seasonal period available for processing. The bridge shows several abnormalities: a) a shifted dilation centre for one segment; b) the western part shows a significantly lower coherence than the eastern part if reference point is in the eastern part and vice versa (the break is at the Berounka river crossing); c) the bridge shows a behaviour related to temperatures at river crossings, however it doesn’t conform with expected linear deformation model. Finding a) is probably due to construction aspects; understanding of b), c) should be improved by longer monitoring period allowing especially to distinguish between linear deformation and thermal deformation components. Based on the experience acquired from the application of MTI techniques for bridge displacement monitoring and on the lack of deep insight into its particularities in current literature, we proposed an original approach using: A) a method to refine temperature adjustments based on interferogram residuals left after thermal component removal; and B) the applicability of mathematical thermal dilation model into InSAR processing chain. This approach was presented in the article (refer to attachment of the report). Results well indicate detectability of motorway bridge infrastructure using MTI data and methods. Appropriate density of high-coherence persistent scatterer (coh>0.8) was reached for the bridge. From plotted time series of deformation velocities for identified persistent scatterer points the progress of detected movement in LOS during the year is clearly visible. Patterns related to deformations in LOS are clearly visible in the maps of persistent scatterer points. Velocities are, however, related mostly to thermal dilatation component. Linear component deformation could not be identified; therefore, linear deformation of the bridge construction has not been proved using one year time series of TerraSAR-X data. Based on the experience from other research, it is expected, that by using of longer time series of InSAR data linear deformation component would be better separable (if present). Moreover, comparison of 2- or 3-year time series could identify any abnormalities of construction behaviour (both linear and non-linear).

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