臺灣因位於板塊碰撞帶及人為超抽地下水，歷年來皆有不少地表變形，若能有效地大範圍偵測地表變形，可有助於減少災害的發生。合成孔徑雷達差分干涉技術(InSAR)常被利用來偵測公釐至公分等級的地表微變，在過去許多研究中皆證明它能觀測地表大範圍且精準的三維變動。歐洲太空總署提供的Sentinel-1衛星提供C波段合成孔徑雷達影像，並擁有大範圍覆蓋面積及短再訪週期的特性，可快速且有效地取得全臺地表變形圖。然而，臺灣位於電離層赤道異常地區，電離層中全電子含量(Total Electron Content, TEC)的多寡會影響到干涉圖中的相位，進而影響到後續的變形分析。因此，透過Sentinel-1衛星影像，配合全球性、區域性TEC地圖以及頻譜拆解法(split-spectrum)的電離層資料進行修正，可針對全臺進行大範圍的地表變形作進一步、長時間序列的監測。本整合計畫擬提升InSAR對地觀測的精度，透過不同修正量的精度提升，對於相位上的誤差進行改正，以獲得較佳的視衛星方向(line-of-sight, LOS)精度，並整合不同的地面觀測，產製地真資料的參考變形，最後整合雷達與地表觀測，探討視衛星至垂直向的反投影流程，以獲得最終的時序垂直地表變形。因此本整合計畫可分為三項子計畫：(1)提升雷達衛星對地觀測精度，(2)整合地表時空間觀測資料，(3)結合雷達干涉與地面資料，透過變形觀測>電離層改正>地表驗證>變形誤差估計>電離層影響評估>逆推電離層>改善變形觀測等循環式迭代流程，提升地表變形觀測與電離層模式兩者之精度，將有益於各種測地方法。本計畫最終除改善不同波長雷達衛星之觀測精度外，也將整合福衛七號掩星事件所測得電子密度剖面，在轉換至垂直總電子含量後，與GNSS觀測及Sentinel-1反演之電離層橫向整合，提升電離層地圖精度。 ;Taiwan suffers from surface deformation for a long time owing to the anthropogenic forcing and its peculiar location between two convergent plates. A systematic monitoring method observing land deformation for the entire Taiwan using advanced remote sensing technology is needed. Sentinel-1 satellite launched by the European Space Agency (ESA) is operated in C-band SAR data. Taking advantage of the broad coverage and short revisit time of Sentinel-1, we can generate interferograms in a rapid and effectively manner for the entire Taiwan. However, Taiwan is situated on the north edge of the Equatorial Ionization Anomaly (EIA) region. The Total Electron Content (TEC) irregularity between snapshots may cause ionospheric effect in the interferograms. The ionospheric residuals induce extra fringes in the interferograms that further affect displacement result. Therefore, our objective is to use global and regional ionospheric data to correct the Sentinel-1 interferogram, aiming to construct a series of ionosphere-corrected displacement for further analysis. This integrated proposal includes three parts: (1) Improving observational accuracy in radar satellite, (2) Integrating spatiotemporal measurements on the ground, and (3) Synthetic usage of spaceborne and ground observations. It follows an iterative procedure, such as: deformation monitoring > ionospheric correction > ground truth validation > deformation error estimate > ionospheric effect recovery > ionosphere TEC estimate > improved deformation monitoring. We will also integrate TEC retrieved from Formorsat-7 occultation events to improve the accuracy of local TEC map, which will eventually help on other geodetic measurements.
