Using Sentinel-1Interferometry with Regional Ionosphere Correction for Land Displacement Detection in Taiwan

Autor: Wan-Ting Liao, 廖婉婷
Rok vydání: 2018
Druh dokumentu: 學位論文 ; thesis
Popis: 106
Taiwan is located at the convergent boundary between the Eurasian Plate and the Philippine Sea Plate. This tectonically active region produces high surface deformation rate and fault activities. In addition, over-pumping of groundwater for agriculture and aquaculture needs in the southwestern part of Taiwan has induced extra land subsidence in the past 20 years. A systematic monitoring method for land deformation using advanced remote sensing technology is thus needed. The Differential Interferometric Synthetic Aperture Radar (DInSAR) technique has been proven useful to measure surface deformation in an effectively way. Sentinel-1A satellite launched by the European Space Agency (ESA) is one of them acquiring images with various pre-defined scenarios to serve different thematic domains. It operates mostly in the Interferometric Wide Swath (IW) mode with dual polarization in east Asia, which provides a broad coverage with 250 km in range and 170 km in azimuth direction. It orbit characteristics allow users to produce interferograms for most of terrestrial areas every 12 days. However, Taiwan is situated on the north edge of the Equatorial Ionization Anomaly (EIA) Region. The Total Electron Content (TEC) irregularity between snapshots causes ionospheric effect on the interferograms. The ionospheric residuals induce extra fringes in the interferograms that further affect unwrapping and displacement result. In this study, we utilize global and regional ionospheric vertical TEC maps, namely the Global Ionosphere Map (GIM) released by the International GNSS Service and the Taiwan Regional Ionospheric Map (TRIM) provided by the Ionospheric Radio Science Laboratory of National Central University, to compensate ionospheric phase in the interferograms. Our results show that TRIM is capable to reduce most of extra fringes caused by the ionospheric effect. Comparing these two types of TEC map, TRIM presents more accurate and detailed ionospheric patterns than GIM. In a series of 47 interferograms generated from Sentinel-1A ascending mode in 2016–2017, we conclude that when the TEC gradient in south-north direction exceeds 16 TECU (1016 electrons/m2), it will cause extra fringes in the interferogram. Finally, the Global Positioning System (GPS) continuous station measurements are used to compare with DInSAR displacement for the performance of ionospheric correction. The results show that after correction the displacement is more consistent with ground truth. It also confirms that the ionosphere may cause serious error in the displacement estimates. After ionospheric correction, the root-mean-square error (RMSE) of estimated vertical motion is reduced from 42 mm to 11 mm.
Databáze: Networked Digital Library of Theses & Dissertations
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