- freely available
Remote Sens. 2016, 8(12), 1021; https://doi.org/10.3390/rs8121021
2. Description of the Study Area and SAR Dataset
2.1. Study Area
2.2 Dataset and Data Pre-Processing
3.1. The PSI Technology
3.2. Point Target Extraction in a Low-Coherence Area
- Initial pixel candidates are selected based on the amplitude stability of individual pixels, using a higher amplitude dispersion threshold value (0.4).
- Preliminary elimination of pixel candidates is then carried out based on the phase stability of the pixels. High coherence PS candidates are chosen by iteration using the coherence-like coefficient method .
- A standard deviation (STD) threshold for the phase is set for PS candidates to exclude pseudo PS points; in the case of Pudong International Airport, points with phase STDs larger than the indicated threshold value (>0.7) were considered as unstable points and rejected.
3.3. Phase Analysis and Deformation Calculation
4. Results and Reliability Analysis
4.1. InSAR-Derived Results
- The first runway has a moderate deformation status with little change in deformation characteristics. The maximum deformation rates in the first runway area was approximately −1.5 cm/year;
- The second runway shows the most serious deformation among the three runways. Different degrees of uneven deformation rates can be seen in both the north-south profile and east-west profile.
- The third runway has the most complex difference in deformation rates among the three runways. It has a relatively large deformation gradient in the east-west direction. The displacement in the P7 area was approximately −0.5 cm/year, while the displacement in the P8 area was more than −2.5 cm/year, a 2.0 cm/year difference.
4.2. Reliability Analysis of the Derived Deformation
5.1. Runways Subgrade
- The first runway was put into use in 1999; since then, the subgrade settlement of the runway remained large; subsequently the average cumulative deformation reached 59 cm by 2009. However, during this period, the deformation rate also displayed a slight slowing trend. After more than a decade of consolidation effects of the soft clay, we can infer that the foundation settlement rate should have continuous decreased during the study period . As shown in the deformation result plotted in Figure 4, InSAR results of the ground settlement continued to slow from September 2011 to October 2012, to less than 1.5 cm/year.
- The second runway, in operation since 2005, lies in the eastern part of the reclaimed land of the airport. The time over which the land formed here was the shortest; the foundation of the second runway was not formed until a 2001 reclamation project . Due to this kind of weak basic geology, the second runway exhibited the most serious deformation, with a maximum deformation rate greater than 2.5 cm/year.
- The third runway, lying to the west of the first runway, was completed in 2008, with a foundation relatively similar to the first runway. However, since it was completed nine years later than the first runway, the geological base itself still needs further consolidation. Consequently, the third runway underwent more pronounced settlement than the first runway, with a maximum deformation rate greater than 2 cm/year.
5.2. Geological Environment
5.2.2. Seawater Influence
5.2.3. Static Load
- The geological foundation.
- Construction time. Under similar geological conditions (e.g., the first and the third runway), the later the time of completion (the third runway), the more serious soil un-compaction and the larger the settlement will be.
- Paleo-rivers. The soil around the paleo-rivers is weaker than that in other places, thus the paleo-river is an important factor causing inhomogeneous deformation at the airport.
- Seawater influence. The side of the airport closer to the sea experiences seawater influence, such as salt-water intrusion and flushing corrosion, and thus is weaker than other sides of the airport.
- Static load. This is likely the primary factor contributing to the uniform deformation pattern found in the third runway area.
5.3. Potential and Notes of InSAR in Monitoring Coastal Subsidence
Conflicts of Interest
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|No.||Acquisition Date||Orbit||Time Baseline (Days)||Perpendicular Baseline (m)|
|1||27 September 2011||23,772||−66||−26|
|2||19 October 2011||24,106||−44||22|
|3||10 November 2011||24,440||−22||−41|
|4||2 December 2011||24,774||0||0|
|5||24 December 2011||25,108||22||157|
|6||26 January 2012||25,609||55||−60|
|7||28 February 2012||26,110||88||−159|
|8||21 March 2012||26,444||110||117|
|9||12 April 2012||26,778||132||119|
|10||26 May 2012||27,446||176||102|
|11||9 July 2012||28,114||220||−31|
|12||31 July 2012||28,448||242||50|
|13||13 September 2012||29,116||286||−71|
|14||24 September 2012||29,283||297||38|
|15||16 October 2012||29,617||319||59|
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