InSAR Reveals Land Deformation at Guangzhou and Foshan, China between 2011 and 2017 with COSMO-SkyMed Data

Alex Ng,Yiwei Dai,Kui Zhang,Linlin Ge,Zheyuan Du,Wenbin Chen,Hua Wang,Carolina Pagli

doi:10.3390/rs10060813

Abstract

Subsidence from groundwater extraction and underground tunnel excavation has been known for more than a decade in Guangzhou and Foshan, but past studies have only monitored the subsidence patterns as far as 2011 using InSAR. In this study, the deformation occurring during the most recent time-period between 2011 and 2017 has been measured using COSMO-SkyMed (CSK) to understand if changes in temporal and spatial patterns of subsidence rates occurred. Using InSAR time-series analysis (TS-InSAR), we found that significant surface displacement rates occurred in the study area varying from −35 mm/year (subsidence) to 10 mm/year (uplift). The 2011–2017 TS-InSAR results were compared to two separate TS-InSAR analyses (2011–2013, and 2013–2017). Our CSK TS-InSAR results are in broad agreement with previous ENVISAT results and levelling data, strengthening our conclusion that localised subsidence phenomena occurs at different locations in Guangzhou and Foshan. A comparison between temporal and spatial patterns of deformations from our TS-InSAR measurements and different land use types in Guangzhou shows that there is no clear relationship between them. Many local scale deformation zones have been identified related to different phenomena. The majority of deformations is related to excessive groundwater extraction for agricultural and industrial purposes but subsidence in areas of subway construction also occurred. Furthermore, a detailed analysis on the sinkhole collapse in early 2018 has been conducted, suggesting that surface loading may be a controlling factor of the subsidence, especially along the road and highway. Roads and highways with similar subsidence phenomenon are identified. Continuous monitoring of the deforming areas identified by our analysis is important to measure the magnitude and spatial pattern of the evolving deformations in order to minimise the risk and hazards of land subsidence.

Highlights

Many large deltas in the world have been experiencing subsidence because of soil consolidation and compaction, water extraction, and underground tunnelling driven by the rapid economic and population growth [1,2]
This study aims to investigate the deformation in Guangzhou and Foshan between 2011 and 2017 using X-band COSMO-SkyMed (CSK) SAR data, which can provide much higher resolution than the C-band Envisat and L-band ALOS satellites previously used in the region
Based on previous studies [4,26], most of the surface deformation in the study area are expected to be focused on relatively small areas with a radius of a few kilometres and with a magnitude of the deformation of less than ~20 mm/year. Another focus of this paper is to study the urban areas of Guangzhou and Foshan where the temporal decorrelation is not an issue compared to areas with dense vegetation cover

Summary

Introduction

Many large deltas in the world have been experiencing subsidence because of soil consolidation and compaction, water extraction, and underground tunnelling driven by the rapid economic and population growth [1,2]. These deltas accommodate a large percentage of the human population, significant subsidence can cause serious problems to buildings and infrastructures, generating tension cracks. This, together with the continually increasing sea level rise and ground subsidence, puts the local population under a greater risk of environmental problems, such as flooding and saltwater intrusion. Systematic analysis of the land subsidence in Guangzhou and its neighbour, Foshan, is, required for subsidence risk assessment and mitigation

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