Abstract
Land subsidence, as one of the engineering geological problems in the world, is generally caused by compression of unconsolidated strata due to natural or anthropogenic activities. We employed interferometric point target analysis (IPTA) as a multi-temporal interferometric synthetic aperture radar (MT-InSAR) technique on ascending and descending Sentinel-1A the terrain observation with progressive scans SAR (TOPSAR) images acquired between January 2015 and December 2018 to analyze the spatio-temporal distribution and cause of subsidence in Abbottabad City of Pakistan. The line of sight (LOS) average deformation velocities along ascending and descending orbits were decomposed into vertical velocity fields and compared with geological data, ground water pumping schemes, and precipitation data. The decomposed and averaged vertical velocity results showed significant subsidence in most of the urban areas in the city. The most severe subsidence was observed close to old Karakorum highway, where the subsidence rate varied up to −6.5 cm/year. The subsidence bowl profiles along W–E and S–N transects showed a relationship with the locations of some water pumping stations. The monitored LOS time series histories along an ascending orbit showed a close correlation with the rainfall during the investigation period. Comparative analysis of this uneven prominent subsidence with geological and precipitation data reflected that the subsidence in the Abbottabad city was mainly related to anthropogenic activities, overexploitation of water, and consolidation of soil layer. The study represents the first ever evidence of land subsidence and its causes in the region that will support the local government as well as decision and policy makers for better planning to overcome problems of overflowing drains, sewage system, littered roads/streets, and sinking land in the city.
Highlights
Ground subsidence is a common geological hazard worldwide, which is mostly linked to natural or anthropogenic processes [1]
A step-wise and iterative technique, i.e., interferometric point target analysis (IPTA) multi-baseline technique of persistent scatterer interferometry (PSI), is implemented on Sentinel -1 (4 season × 4 years) data acquired between January 2015 and December 2018 along ascending and descending orbits in order to investigate, highlight, and understand the causes of subsidence and its temporal evolution in response to increasing demand of ground water and changes in soil properties in Abbottabad city of Pakistan (Figure 1)
The phase model used for point target analysis is the same as that used in conventional interferometry, its step-wise iterative process is very helpful in refining the parameters and to separate the deformation phase from all non-deformation phase components of Equation (1) [36]
Summary
Ground subsidence is a common geological hazard worldwide, which is mostly linked to natural (e.g., earthquake, compression of soil, and change in aquifer) or anthropogenic (e.g., underground construction activities, groundwater extraction) processes [1]. Changes in geological settings, mining, construction of subways, and ground water extraction are among the main causes of land subsidence in most cities in the world [3,4]. A step-wise and iterative technique, i.e., interferometric point target analysis (IPTA) multi-baseline technique of persistent scatterer interferometry (PSI), is implemented on Sentinel -1 (4 season × 4 years) data acquired between January 2015 and December 2018 along ascending and descending orbits in order to investigate, highlight, and understand the causes of subsidence and its temporal evolution in response to increasing demand of ground water and changes in soil properties in Abbottabad city of Pakistan (Figure 1). Advanced InSAR processing software, GAMMA-2017®, developed by GAMMA Remote Sensing AG, Switzerland, was used to define and implement the IPTA processing chain for the mapping of ground subsidence in the area
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