Abstract
Middle-sized earth- and rock-filled dams with clay cores continue to settle by approximately 0.5–1.5% of their height for approximately 1–3 years after their construction phase. This paper investigates the use of high-resolution spaceborne Synthetic aperture Radar (SAR) interferometry to monitor this settlement process, with the case of the Gongming dam in China. The varieties of slope foreshortening and stretching in the radar coordinates are attributed to the radar’s local incidence angle and the dam’s slope heading, which are analysed in detail. Focusing on the embankment slope settlement analysis, the equations for calculating foreshortening and the line-of-sight deformation decomposition are derived in detail for the adjustment and data fusing. The scattering characteristics of different materials on the dam surface are analysed, including the grass slope, concrete slope, top road (crest), top wall, step, and ditch. According to the analysis of the precipitation data from a local meteorological station, the coherence losses on the slopes are mainly caused by surface moisture. Both the TerraSAR-X Spotlight (TSX-SL) data and the COSMO-SkyMed Strip Mode (CSK-SM) data are analysed by the stacking method to assess the slopes’ deformations. The TSX-SL data results show the highest rate of settlement as 2 cm/yr on the top of the dam slope, consistent with the clay core shrinking process. The CSK-SM data show a similar trend in the lower part of the dam slope but underestimate the deformation in the upper part of the slope.
Highlights
Spaceborne interferometrical Synthetic aperture Radar (InSAR) is an established technique to assess ground surface deformation for a wide range of applications related to natural and man-made hazards [1,2,3]
Examples include the big concrete gravity dams in three gorge dams in China [4]; the big concrete face rock-fill dam (CFRD) in Shuibuya, China [5,6]; the big arch dam in Pertusillon, Italy [7]; some big earth- and rock-filled dams with clay cores, such as those in Mosul [8] and Darbandikhan [9] in Iraq, Mornos in Greece [10], and Disueri [11] and Conza della Campania in Italy [12]; and the Masjed–Soleyman dam in Iran [13]
The InSAR time-series methods of Persistent Scatterer (PS) [16] and Small Baseline Subset (SBAS) [17] are the main tools for all these case studies, as the PS and Distributed Scatterer (DS) [18] points on the dams are key for precise deformation analysis and comparison with traditional surveying techniques, such as GPS and levelling
Summary
Spaceborne interferometrical Synthetic aperture Radar (InSAR) is an established technique to assess ground surface deformation for a wide range of applications related to natural and man-made hazards [1,2,3]. The InSAR analysis of the Masjed–Soleyman dam [13] showed that high resolution TerraSAR-X Spotlight (TSX-SL) X-band interferograms provide a complete, detailed picture of the occurrences on the crest and embankment, which cannot be observed by the interpolated results derived from GPS or levelling benchmarks It showed the limitation of the SAR foreshortening and the rapid deformation on the dam top that may cause squeezing of the fringes on the dam surface in near-range geometry. TRhaenddeDfoermcoamtipoonsrietisounltsofdtehreivDedamfroSmettthleemIneSnAt R time series are in the radar line-of-sight direction, which should be adjusted by the slopes’ angle, local incidence angle, and azimBuythkdniorwecitniognt.he geometry of the dam faces and the SAR payload parameters, the following equations can be used to calculate the distortions caused by foreshortening and s2h.1a.dSolwopiengG.eoTmheetrsyetDtliesmtoretniot-ninduced deformation on the dam slopes can be decomposed into the radarTlhineel-oocfa-slitgohptodgerfaoprhmyaatinodntbhye gtheeolloogcyaloifntchide egnrcoeunadngblaes, etmheendtamareaiznimfluuetnhtiaanl gfalec,toarnsd[2t3h]efoslrotphee acnognlsetrfuoclltoiowninogf eEmqubaatnioknm(e7n).t Tdhaemdse.
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