MONITORING LAND SUBSIDENCE EVOLUTION IN THE CENTRAL URBAN REGION OF HANOI CITY, VIETNAM

Applying the persistent scatterer interferometric synthetic aperture radar (PSInSAR) approach, land subsidence in the central urban region of Hanoi city is monitored from 2007 to 2019 by using 21 ALOS-1 images acquired from February 2007 to February 2011 and 51 Sentinel-1 images acquired from April 2016 to September 2019. The average velocity maps of land subsidence in the line of sight (LOS) of the satellite show the contrast in the land subsidence of the northern and southern banks of the Red River: in the first period, the northern bank is quite stable, while some areas subside at remarkable velocities on the southern bank, where many construction works have occurred and groundwater has been strongly exploited over the past decades. The ground is deformed in three main areas: Hoang Mai, Ha DongThanh Xuan, and Nam Tu Liem-Hoai Duc. The PSInSAR results also show some small subsidence areas downtown. In the second period, the ground surface remains stable on the northern bank of the Red River, and land subsidence occurs mainly on the southern bank in comparison with that of the previous period. However, the subsidence velocity decreases and only presents two main subsidence areas in Ha Dong-Thanh Xuan, and Nam Tu Liem-Hoai Duc, while subsidence significantly weakens in Hoang Mai. The results obtained from the PSInSAR approach correspond to the in situ measurements taken in the period 2007-2008 by the leveling method. This correspondence indicates the ability to apply multitemporal and multi-SAR system data for monitoring land subsidence in large urban areas over a long time with high reliability and reasonable cost