Satellite-Based Monitoring of Land Subsidence in the Twin Cities of Pakistan Using Sentinel-1A SAR Data Muhammad Abid and Muhammad Farooq Iqbal
Applied Geo-Informatics Research Lab, Department of Meteorology, COMSATS University Islamabad (CUI), Islamabad, Pakistan
Abstract
Ground deformation and land subsidence have emerged as significant geo-environmental hazards, leading to substantial economic losses in many major cities worldwide. Conventional ground-based approaches such as Global Positioning System (GPS), leveling surveys, and other in-situ measurements are reliable for detecting land subsidence. However, these methods are often labor-intensive, time-consuming, and costly. To address these challenges, the use of satellite-based techniques, particularly Synthetic Aperture Radar (SAR), has proven effective for monitoring land subsidence over large areas. This study focuses on detecting and monitoring ground deformation and subsidence in the twin cities of Rawalpindi and Islamabad, Pakistan, from 2018 to 2022, using Sentinel-1A SAR data. Rawalpindi, the fourth-largest city in Pakistan, and its adjacent city Islamabad are experiencing rapid urban expansion. Both the cities heavily depend on groundwater extraction through tube wells as a primary source of water. The overexploitation of groundwater by residents, industries, and municipal authorities has significantly impacted subsurface stability. The study utilized Differential Interferometric SAR (DInSAR) techniques, employing Interferometric Wide (IW) Single Look Complex (SLC) images from Sentinel-1A^s C-band sensor. Successive image pairings were generated between January 2018 to January 2022. The analysis focused on determining displacement in both the Line of Sight (LOS) and vertical direction. Findings revealed that average LOS displacement ranged from -97 mm to +76 mm, while average vertical displacement ranged from +102.39 mm to -80.37 mm during the study period. Significant land subsidence was observed in the southern section of Rawalpindi, particularly in the Old Rawalpindi area, which is characterized by high population density and extensive groundwater usage. Conversely, parts of Islamabad showed signs of uplift, possibly due to variations in underground aquifer recharge and geological factors. The study suggests that excessive groundwater extraction, urbanization, and underlying geological and lithological conditions are the primary drivers of the observed surface deformations.
Keywords: Synthetic Aperture Radar (SAR), Sentinel-1, Differential Interferometric SAR (DlnSAR), Land Deformation, Subsidence
