| 摘要: | 2022 年 9 月17日與18日，臺東關山及池上地區先後發生淺層地震，
造成顯著的地表破裂與明顯地表形變。本研究運用差分干涉合成孔徑雷達
（Differential Interferometric Synthetic Aperture Radar, DInSAR）技術，分析地震引致之形變分布。資料來源為ALOS-2衛星於震前（2022年4月3日)及震後（2022年9月18日）之下降軌道影像，涵蓋9月17日規模Mw 6.6、震源深度約7.8公里之主震事件。
DInSAR 透過對兩期雷達影像進行干涉處理，可有效解析地表位移。然
而，除了真實形變訊號外，干涉相位亦會受到如電離層效應與地形影響等誤
差項干擾。電離層效應係由於衛星訊號於通過電離層時產生相位延遲，尤其
在總電子含量（Total Electron Content, TEC）梯度明顯時，易於干涉圖中形成非形變造成之相位條紋。臺灣位處於赤道電離層異常(Equatorial Ionization Anomaly, EIA）北緣，TEC 變異性較高，使得電離層修正在本區域尤為重要。
為有效修正電離層誤差，本研究採用中央氣象局（Central Weather Administration (CWA)）所提供之臺灣區域電離層地圖（Taiwan Regional Ionospheric Map, TRIM）之 TEC 資料。考量信號穿越電離層之高度變化，本研究以最大電子濃度高度（hmF2）分布作為電離層穿透視窗，並於修正過程中引入權重矩陣以因應信號路徑可能為斜向或曲折。經修正後，可有效去除電離層對相位訊號之干擾，進一步取得較為精確之同震地表形變資訊。;On September 17 and 18, 2022, shallow earthquakes struck Guanshan and Chihshang, respectively, causing significant surface ruptures and noticeable ground deformation. We used Differential Interferometric Synthetic Aperture Radar (DInSAR) technology to analyze the deformation pattern. This study employed ALOS-2 satellite images captured in the descending track before (April 3, 2022) and after (September 18, 2022) the earthquake, covering the September 17 event, which had a magnitude of M6.6 and a focal depth of 7.8 km.
Ground displacements can be detected by performing differential interferometry on two radar satellite images. However, besides surface deformation, the measurements also contain errors caused by ionospheric effects, topographic variations, and other factors. The ionospheric errors result from delays as the satellite signal traverses the ionosphere. Taiwan is situated in the Equatorial Ionization Anomaly (EIA) region, where the Total Electron Content (TEC) fluctuates over time due to variations in the EIA. If there is a difference in TEC between the two images, additional phase fringes appear in the interferograms.
To mitigate the ionospheric effects in DInSAR results, this study utilizes the Taiwan Regional Ionospheric Map (TRIM) TEC data provided by the Central Weather Administration (CWA). Given that Taiwan is near the northern boundary of the EIA, ionospheric correction is typically performed using the peak electron density altitude (HmF2) distribution as a penetration window. A weighting matrix is applied during correction since the signal path may be oblique and curved. After ionospheric correction, the accurate coseismic surface deformation can be accurately obtained. |
