錫默盧島(Simeuleu island)為2004年印度洋地震中最接近震央的島嶼之一，在地震發生過後，導致許多國家的土地產生嚴重的垂直變化，其中包含了印度、泰國以及斯里蘭卡等多個國家。在這項研究中，我們利用光學影像並且搭配了一套流程來研究錫默盧島陸地的垂直變化。由於在地震過後珊瑚礁抬升改變了沿岸地形，因此我們收集了多張Landsat系列之光學影像來檢測海岸抬升或是下沉的現象。首先會先收集地震前以及地震後的Landsat影像，並將影像進行全色態加強之前置處理，將綠色波段以及中紅外波段的解析度提高。接著運用改良常態差異水體指標 (MNDWI)來判釋水體與非水體的像素分佈，再計算每一個影像網格中水所出現的機率並使用NAO.99b潮汐模型取得平均較高高潮位 (MHHW)以及平均較低低潮位 (MLLW)之兩條水位線做為高度參考，並運用高度參考值將淹水機率轉換為實際高程資訊。最後將地震前與地震後的兩段時間段作為我們觀察地區變化的時間序列，從結果中顯示位於該島西北部的沿岸地形抬升了幾10公分，而位於東南部的沿岸地形則是下沈約34公分，此外在其他特定區域的沿岸地形也有40公分左右的明顯抬升。;Simeuleu island is one of the islands closest to the epicenter of 2004 Indian Ocean Earthquake. This event is known to cause severe land vertical motion in several countries, such as India, Thailand and Sri Langka. This event had changed the coastal topography that can be seen from the uplift of coral reef. In this study, we aim to investigate land vertical motion in Simeuleu island by employing optical remote sensing imageries and a tide model. A series of Landsat images are collected to detect coastal uplift/subsidence. Landsat surface reflectance (Level 2) of pre-event and post-event are collected to conduct pan-sharpening for increasing spatial resolution of green and mid-infrared band. Next, we calculate the modified normalized difference water index (MNDWI) to identify water and non-water for all images and sum up those images to make an inundation chance. Furthermore, we run the NAO.99b tide model to obtain the mean higher high water (MHHW) and mean lower low water (MLLW) as height references. Finally, the inundation chance with the MHHW and MLLW is linearly inverted to obtain a DEM. To observe the changed region, we divide the image set into two epochs before and after the earthquake. Our result shows that the island experiences uplift in the Alafan at about few tens of centimeters while in the southeast experience subsidence about 34 cm. Some particular spots have obviously stronger uplift at around 40 cm.
