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Summary of Proposal LAN2376

TitleMonitoringof D48 highway and the surrounding slope by Persistent ScatterersInterferometry
Investigator Sustera, Jiri - Gisat, Sales and marketing department
Team Member
Eng. Sustera, Jiri - GISAT s.r.o., Department of Remote Sensing
Mgr. Kolomaznik, Jan - GISAT s.r.o., Department of Remote Sensing
PhD. Eng. 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 related to the slope instability in area of Lysuvky R48 highway segment, Czech Republic. Results should provide synoptic view of deformations in the are both in close vicinity and the neighbouring villages. The project should 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 optionally with corner reflectors utilization. Due to size, character and magnitude of anticipated deformations in the area 24 TerraSAR-X High Resolution SpotLight mode data series from descending track is requested. Deliverables shall comprise both graphical and tabular materials showing resulting identified deformations, presentations and summary report.
Final Report*AOI description * The study area was located in Norhern Moravia, near the Frýdek-Místek city, Czech Republic. Newly built highway R48 connects highway D1 with Poland. When passing along the village Lysuvky, it traverses slight slope, which turned out to be subject to slope instabilities affecting the highway construction elements (tunnel, supportive walls etc.). The slope (to the south) and during the construction, geology of the slope was infringed and instabilities with estimated estimated velocity of centimeters to decimeters per year were expected in the area as was shown in the reports from monitoring by conventional (surface and subsurface) means. * Satellite and ancillary Data * - 24 SpotLight mode scenes on descending track number 17 were ordered - global SRTM DEM was utilized - air temperature values from nearby meteorological weather station were collected. * Processing* After preliminary tests with SBAS technique it was decided to use COTS MTI processing technique satisfying the need to identify both persistent and distributed targets. Therefore, TRE proprietary SqueeSAR™ technique was utilized. SueeSAR™ is a proprietary multi-interferogram technique patented by TRE, providing high precision measurements of surface ground deformation by processing satellite radar images acquired over the same area, during a specific time span. SqueeSAR™ analysed single out measurement points on the ground that were quality point-wise radar targets (referred to as Permanent Scatterers, PS) and spatially distributed scatterers (DS). Exploiting both types of reflectors, this technique not only provided information over areas of stable radar signal return but also over low-reflectivity homogeneous areas (e.g. uncultivated land, debris, deserted areas, etc.) The analysis was carried out using SAR images acquired by the TerraSAR-X satellite during the period 09/05/14 -26/04/15. All displacement measurements were carried out along the sensor's line of sight (LOS). As a part of first round of processing, the demonstration of detectability of if articifical corner reflector was requested by funding agency (TACR) to be conducted. Demonstration was carried out for the scene acquired on 23.11.2014 – metallic tri-hedral corner reflector was temporally installed in the field in slope above the highway. Correct orientation in horizontal and vertical axes was calculated with respect to precise TSX orbit as well as the expected RCS with respect to the reflector material, shape and size. Demonstration should have demonstrate utility both for TerraSAR-X and Sentinel-1, which was being operated in commissioning phase. Sentinel-1 scene had, however, not been collected over the AOI despite the acquisition plan, hence only TSX utility could have been demonstrated. * Results * A total number of 1.739 MP with a point density of 869 MP/Km2 were detected for the 2 km2 of the AOI. The distribution of measurement points (MP) was good but not homogeneous. This is typical for rural areas, such as the one in AOI, where the electromagnetic reflection properties rapidly change in time. It must be noted that no significant evidence of ground or infrastructure element movement was detected by applied method in the AOI. Absence of real slope movements leading to deformation of supportive infrastructure elements (side-walls) go against initial expectation based on reports from formerly conducted field measurements. Taking into account density, homogeneity and reliability of the PS points in the AOI, it is assumed that the expectation of ongoing displacements was wrong. Slope has likely been stabilized by some of applied measures, at least in an extent that it does not affect the supportive infrastructure elements. As a result, the magnitude of residual deformations could be below detectable limits (approximately 2 mm / year as estimated for the dataset and method utilized). Analysis of amplitude changes was conducted to support the interferometric processing. No significant changes in ground reflectivity, which could be related to slope movements were identified. It is possible that magnitude of slope deformation remains relatively high in the slope between the highway and the Lysuvky village. Due to active agriculture practice the area is incoherent therefore could not be monitored by MTI. From this point of view, the test installation of artificial corner reflector conducted is important as it demonstrate the option to the user. Following outputs were prepared: - displacement time series for identified PS/DS; - displacement map- When extending the analysis into the area around the AOI, it was noticed the clearly subsiding area to the northwest from the Lysuvky AOI. The scope of the extended analysis was to provide an extra view of the region, showing potential unknown deformation phenomena. Particularly, the analysis identified an area affected by subsidence in the north-western sector. It was confirmed that the subsidence is related to an underground mine. Despite the subsidence do not affect highway infrastructure, it is valuable finding providing evidence on reliability and potential of the data and method. *Conclusion * The goals of the project were partly reached: - Deformation of infrastructure could not be proved But it has been proven that: - Infrastructure elements are no longer subject to deformation in the whole extent of the AOI (the original extent was not known!) - Slope deformation do not affect or threaten the inhabited area (Lysuvky village) – this fact was not known before the MTI - The infrastructure elements proved to represent highly coherent reflection with appropriate density of MPs . This aspect is especially important for discussing with potential service users regarding future monitoring in this or different AOI - Apart from the deformation maps and plots, it has been proven that reflectivity of the corner reflector was sufficient enough to be identified in the harsh autumn condition when installed in freshly ploughed field with strong temporal reflectivity of the ploughed soil. - Results will be utilized in discussion with Road and Highway administration about set up of future projects/services. Still, they represent not only the input into discussion, but also lessons learnt: initial expectation should be double checked and reference supportive measurement (MTI or field-based) should be considered in case of prior ambiguities.

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