以雷達干涉技術監測雲林地層下陷

Abstract

近年來台灣地區因地下水超抽引發地層下陷問題日趨嚴重，其中雲林地區為嚴重下陷區域之一。位於雲林中部之高鐵沿線土庫鎮及元長鄉下陷速率亦增至平均每年 7 公分。而已通車之高速鐵路穿越雲林地層下陷區，將影響且危害鐵路之行車速率與行車安全。本研究針對雲林下陷的地區進行觀測。近幾年來太空遙測技術應用於大地測量日趨完善，其優點為可於短時間內獲取大片面積的高密度且高精度高程資料，其資料精度也達到公分級的程度。針對雲林下陷區域的監測，研究利用二種方法：(1)雷達差分干涉技術(DInSAR) (2)永久散射體(Persistent Scatterers)干涉技術，其中永久散射體干涉技術，提出兩種方法研究。利用雷達差分干涉技術，可得知為雲林都市地區，地表變化趨勢；而永久散射體干涉技術可進一步解決雷達差分干涉技術的限制與可看到許多細微的變形活動。最後將永久散射體干涉技術得到較佳的結果和水準觀測資料做驗證。初步成果顯示(1)雷達差分干涉技術得到雲林地區運動趨勢，沿海西部相對東部呈現下陷趨勢。(2)在永久散射體技術方法一中，針對高鐵沿線所經過的土庫地區，相對下陷約有最大值 7 cm/yr，約與水準觀測相同。

In Taiwan, land subsidence due to groundwater withdrawal becomes increasingly serious in recent years. Yunlin County is one of the regions with large subsidence. The subsidence rate here has reached a maximum of 7 cm/yr around Tuku and Yuanchang, where the Taiwan High Speed Rail (THSR) passes through. Subsidence may endanger the THSR operation. In this study, the subsidence region in Yunlin was observed using the DInSAR techniques. Recently, remote sensing technique for geodesy has been significantly improved; it is able to sample observations at a high spatial resolution and a high precision. In this study, Differential Interferometry Synthetic Aperture Radar (DInSAR) and the Persistent Scatterer (PS) InSAR were used to observe subsidences in Yunlin. DInSAR gives a two-dimensional surface deformation, but the resolution and precision from DInSAR are degraded by factors such as spatial and temporal de-correlations, and atmospheric effect. PS InSAR overcomes some of the problems in DInSAR and delivers deformations at selected scatterers. The deformations from PS InSAR are compared with deformations from precision leveling. Two conclusions are drawn from this study: (1) The DInSAR result shows that surface subsidence of Yunlin tilts towards the west to the coasts (2) PS InSAR yields a maximum subsidence rate of about 7 cm/yr in Tuku of Yunlin, which is close to the rate from precision leveling .