Abstract
Groundwater is a major source of fresh water in Tianjin Municipality, China. The average rate of groundwater extraction in this area for the last 20 years fluctuates between 0.6 and 0.8 billion cubic meters per year. As a result, significant subsidence has been observed in Tianjin. In this study, C-band Envisat (Environmental Satellite) ASAR (Advanced Synthetic Aperture Radar) images and L-band ALOS (Advanced Land Observing Satellite) PALSAR (Phased Array type L-band Synthetic Aperture Radar) data were employed to recover the Earth’s surface evolution during the period between 2007 and 2009 using InSAR time series techniques. Similar subsidence patterns can be observed in the overlapping area of the ASAR and PALSAR mean velocity maps with a maximum radar line of sight rate of ~170 mm·year−1. The west subsidence is modeled for ground water volume change using Mogi source array. Geological control by major faults on the east subsidence is analyzed. Storage coefficient of the east subsidence is estimated by InSAR displacements and temporal pattern of water level changes. InSAR has proven a useful tool for subsidence monitoring and displacement interpretation associated with underground water usage.
Highlights
Subsidence caused by groundwater extraction is a worldwide problem [1,2,3]
The probability for a pixel to be Persistent Scattering (PS)/slowly decorrelating filtered phase (SDFP) is estimated through phase analysis, which is successively refined in a series of iterations
Two subsidence areas can be identified from the mean velocity map (Figure 2)
Summary
Subsidence caused by groundwater extraction is a worldwide problem [1,2,3]. Estimated subsidence rates range up to several hundred mm per year, highlighting the importance of continuous displacement mapping. With great demand for fresh water and a limited river water resource, ground water use seems inevitable for Tianjin City (Figure 1a), which has a population of 12.93 million and is currently growing at 2.6% per year till 2010 [4]. The annual rates from 1981 to 2007 are in the range. Water extraction has increasingly been from deeper underground [6]. This extensive use of ground water could account for the subsidence in Remote Sens. This extensive use of ground water could account for the subsidence in Remote Sens. 2016, 8, 266; doi:10.3390/rs8030266 www.mdpi.com/journal/remotesensing
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