Abstract
The accurate detection of land subsidence rates in urban areas is important to identify damage-prone areas and provide decision-makers with useful information. Meanwhile, no precise measurements of land subsidence have been undertaken within the coastal Port-Said City in Egypt to evaluate its hazard in relationship to sea-level rise. In order to address this shortcoming, this work introduces and evaluates a methodology that substantially improves small subsidence rate estimations in an urban setting. Eight ALOS/PALSAR-1 scenes were used to estimate the land subsidence rates in Port-Said City, using the Small BAse line Subset (SBAS) DInSAR technique. A stereo pair of ALOS/PRISM was used to generate an accurate DEM to minimize the residual topography effect on the generated interferograms. A total of 347 well distributed ground control points (GCP) were collected in Port-Said City using the leveling instrument to calibrate the generated DEM. Moreover, the eight PALSAR scenes were co-registered using 50 well-distributed GCPs and used to generate 22 interferogram pairs. These PALSAR interferograms were subsequently filtered and used together with the coherence data to calculate the phase unwrapping. The phase-unwrapped interferogram-pairs were then evaluated to discard four interferograms that were affected by phase jumps and phase ramps. Results confirmed that using an accurate DEM (ALOS/PRISM) was essential for accurately detecting small deformations. The vertical displacement rate during the investigated period (2007–2010) was estimated to be −28 mm. The results further indicate that the northern area of Port-Said City has been subjected to higher land subsidence rates compared to the southern area. Such land subsidence rates might induce significant environmental changes with respect to sea-level rise.
Highlights
IntroductionDifferential Interferometry Synthetic Aperture Radar (DInSAR) is a technique which can measure the vertical ground movement of an area in millimeter accuracy [1]
A number of researchers have been interested in measuring land subsidence rates in the Nile Delta region by using radar interferometric techniques [15,19,31,38,39,43]
Located at northeastern side of the Nile Delta, it was chosen as a representative coastal city to estimate the modern land subsidence rate
Summary
Differential Interferometry Synthetic Aperture Radar (DInSAR) is a technique which can measure the vertical ground movement of an area in millimeter accuracy [1]. In the last decade a number of Synthetic Aperture Radar (SAR) space-borne satellites have been launched and operated using different wavelengths and polarizations. These repeat-pass interferometric SAR (InSAR) systems have repeatedly proven their efficiency due to their high precision and high spatial resolution [1,2,3]. When the SAR system images the ground, both amplitude (strength) and phase (time) of the backscattered signals are recorded by the receiving antenna.
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