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Paper title Assessment of ground subsidence patterns in the Manila NCR and lower Pampanga river basin using persistent scatterers interferometry
Authors
  1. Jan Kolomazník GISAT s.r.o. Speaker
  2. Ivana Hlavacova GISAT
  3. Juraj Struhár Gisat
Form of presentation Poster
Topics
  • D1. Managing Risks
    • D1.01 Satellite EO for Geohazard Risks
Abstract text The Copernicus EMS-FLEX service was activated by a request from the authorized user and a local user from the Philippines. Several sources suggest that the Manila NCR and lower Pampanga river basin in the Philippines have been affected by ground subsidence phenomena impacting settlements in the Manila agglomeration, increasing riverine and coastal flood risk. The EMS service provided evidence of ground motion patterns in the targeted areas using multi-temporal satellite interferometry and persistent scatterers technique. Tailored products derived from time series of multi-pass Sentinel-1 imagery provide insight into localization and extent of sinking zones and quantify the severity of phenomena related to estimated motion velocity or additional adversary patterns.
It is generally assumed that the subsidence in the area is strongly related to underground water extraction, which was increasing rapidly during the last decades. But, as measures to mitigate the subsidence were already taken, the highest concern was required in getting the information about the dynamics of the subsidence trend, i.e. whether it is slowing or accelerating. PSI processing over 6 years-stack generated a high number of unwrapping errors on persistent scatterers with non-linear motions. Errors had to be corrected before the estimation of the motion trend dynamics. In addition, temporally coherent targets were detected to avoid losing information by decorrelation over limited periods from a long time series of interferometric measurements. Intervals showing high levels of noise had been detected and were not considered in the process of estimation of the motion trend dynamics.
Apart from ground motion rates and displacements in the line-of-sight, vertical and east-west horizontal motion fields were estimated using directional decomposition. Initially, only limited horizontal movements were expected in the area of interest as groundwater extraction is typically followed by vertical subsidence. However, the area was hit by at least one earthquake during the observation period, in addition, there might be long-term residual horizontal tectonic motions along the slips. Abrupt non-linear motion resulting from the earthquake was probably partially eliminated from the resulting time series by the atmospheric phase screen. Though, patterns of non-vertical motions were detected and presented in the results.
The service outputs are utilized by local research teams to evaluate the extent of subsidence phenomena, their severity, and potential impacts on existing settlements and planned projects (land reclamation). Results shall provide information baseline into the research of potential subsidence driving factors such as the correlation between groundwater extraction and subsidence rates and spatial-temporal patterns.