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Surface Deformation from Sentinel-1A InSAR: Relation to Seasonal Groundwater Extraction and Rainfall in Central Taiwan

1
Department of Civil Engineering, National Chiao Tung University, 1001 Ta Hsueh Rd., Hsinchu City 30010, Taiwan
2
Positioning and Community Safety Division, Geoscience Australia, GPO Box 378, Canberra ACT 2601, Australia
3
Department of Earth Sciences, National Central University, No. 300, Jhongda Rd., Jhongli City, Taoyuan County 32001, Taiwan
*
Author to whom correspondence should be addressed.
Remote Sens. 2019, 11(23), 2817; https://doi.org/10.3390/rs11232817
Received: 21 October 2019 / Revised: 13 November 2019 / Accepted: 25 November 2019 / Published: 28 November 2019
Extracting groundwater for agricultural, aquacultural, and industrial use in central Taiwan has caused large-scale land subsidence that poses a threat to the operation of the Taiwan High Speed Railway near Yunlin County. We detected Yunlin subsidence using the Sentinel-1A Synthetic Aperture Radar (SAR) by the Small BAseline Subset (SBAS) method from April 2016 to April 2017. We calibrated the initial InSAR-derived displacement rates using GPS measurements and reduced the velocity difference between the two sensors from 15.0 to 8.5 mm/a. In Yunlin’s severe subsidence regions, cumulative displacements from InSAR and GPS showed that the dry-season subsidence contributed 60%–74% of the annual subsidence. The InSAR-derived vertical velocities matched the velocities from leveling to better than 10 mm/a. In regions with few leveling measurements, InSAR increased the spatial resolution of the vertical velocity field and identified two previously unknown subsidence spots over an industrial zone and steel factory. Annual significant subsidence areas (subsidence rate > 30 mm/a) from leveling from 2011 to 2017 increased with the declining dry-season rainfalls, suggesting that the dry-season rainfall was the deciding factor for land subsidence. A severe drought in 2015 (an El Niño year) dramatically increased the significant subsidence area to 659 km2. Both InSAR and leveling detected similarly significant subsidence areas in 2017, showing that InSAR was an effective technique for assessing whether a subsidence mitigation measure worked. The newly opened Hushan Reservoir can supply surface water during dry seasons and droughts to counter rain shortage and can thereby potentially reduce land subsidence caused by groundwater extraction. View Full-Text
Keywords: Hushan Reservoir; land subsidence; Sentinel-1; SBAS; Yunlin Hushan Reservoir; land subsidence; Sentinel-1; SBAS; Yunlin
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MDPI and ACS Style

Yang, Y.-J.; Hwang, C.; Hung, W.-C.; Fuhrmann, T.; Chen, Y.-A.; Wei, S.-H. Surface Deformation from Sentinel-1A InSAR: Relation to Seasonal Groundwater Extraction and Rainfall in Central Taiwan. Remote Sens. 2019, 11, 2817.

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