自21世紀以來，許多發展中國家的城市發展迅速，不僅改變了環境和景觀，亦對地表變形產生了很大的影響。為了要觀測地表變形，傳統的大地測量技術利用低空間取樣密度和高成本的量測方式，無法有效地捕獲這種加速度的變形量。因此，稱為干涉合成孔徑雷達（InSAR）的衛星遙測技術被廣泛部署，並證明具有高精度和廣泛覆蓋的能力。在歐洲太空總署（ESA）成功發射Sentinel系列以及提供免費影像之後，世界上許多城市地區都可以廣泛應用遙測影像。近年來，越南的河內市的發展在世界城市中名列前茅，但市區顯著的擴張導致了廣泛的表面變形。本研究利用Sentinel-1雷達衛星的優勢，透過衛星的短時間重訪週期來監測地表地面位移，以2016-1018期間Sentinel-1對地形進行觀測和逐行掃描（TOPS）合成孔徑雷達數據，並使用最小基線長（SBAS）技術檢視河內地區在十年城市規劃下的地面沉降現象(2008年行政邊界最新擴張後，第一個10年城市規劃結束)，我們欲測量在早期文獻中報導的河內市區及郊區的沉降率。SBAS變形結果表明，許多沉降區域在市中心邊界附近已達到50毫米/年，並顯示在中央地區約有10毫米/年輕微下陷率，邊界的南側地區則有27~37毫米/年的下陷，也可透過雷達干涉的時間序列研究下陷區域變化趨勢。與此同時，本研究也找到了數個新的下陷區域，並提出了相應的因素，對於未來的城市規劃，可提供了巨大的潛在價值，以緩解這一現象及其對高成本基礎設施的影響，提供基礎設施維護和保險的基本信息。;Using Sentinel-1 TOPS SAR and SBAS for Land Subsidence Monitoring in Hanoi, Vietnam
Rapid urban development in many developing countries has been undergoing since the beginning of 21st century. It has not only altered the environment and landscape, but also strongly influenced the ground surface deformation. The traditional geodetic techniques have not been able to efficiently capture this acceleration due to the low spatial sampling density and high cost. Hence, one of satellite remote sensing techniques called the Interferometric Synthetic Aperture Radar (InSAR) is broadly deployed and proved the capability of high accuracy and wide coverage. After the successful launch of Sentinel series by the European Space Agency (ESA) along with free data access, the wide application of remotely sensed imagery is available to many urban areas in the world. Hanoi city in Vietnam is ranked in the top of world’s urban growth in recent years. As a result, there is a remarkable expansion of urban area that leads to broad surface deformation. Taking the advantages of Sentinel-1 radar satellite, the monitoring of surficial ground displacement has been possible in a short time with regular revisit cycles. This study utilizes Sentinel-1’s Terrain Observation with Progressive Scan (TOPS) SAR data to detect the land subsidence using Small Baseline Subset (SBAS) technique over Hanoi in the period 2016-1018, when the first 10-years urban planning ended after the latest expansion of administrative boundary in 2008. We intend to measure the subsidence rates in urban and suburban regions of Hanoi, which were reported in the earlier literature. The results show that many subsided areas reach 50 mm yr-1 near the border of city center. The report of slight subsidence around 10 mm yr-1 in the central and a range from 27 to 37 mm yr-1 in consecutive subsiding areas located the south of administrative boundary also are highlighted by SBAS deformation map. An extended time series of subsiding zones have been investigated. Meanwhile, several new declining areas have been found and the corresponding factors are suggested. For future urban planning, this study contributes a great potential value which can mitigate this phenomenon and its impact on the high-cost infrastructure. The study also offers the fundamental information for infrastructure maintenance and insurance.
