Abstract
Iran, as a semi-arid and arid country, has a water challenge in the recent decades and underground water extraction has been increased because of improper developments in the agricultural sector. Thus, detection and measurement of ground subsidence in major plains is of great importance for hazard mitigation purposes. In this study, we carried out a time series small baseline subset (SBAS) interferometric synthetic aperture radar (InSAR) analysis of 15 L-band PALSAR-2 images acquired from ascending orbits of the ALOS-2 satellite between 2015 and 2020 to investigate long-term ground displacements in East Azerbaijan Province, Iran. We found that two major parts of the study area (Tabriz and Shabestar plains) are subsiding, where the mean and maximum vertical subsidence rates are −10 and −98 mm/year, respectively. The results revealed that the visible subsidence patterns in the study area are associated with either anthropogenic activities (e.g., underground water usage) or presence of compressible soils along the Tabriz–Shabestar and Tabriz–Azarshahr railways. This implies that infrastructure such as railways and roads is vulnerable if progressive ground subsidence takes over the whole area. The SBAS results deduced from L-band PALSAR-2 data were validated with field observations and compared with C-band Sentinel-1 results for the same period. The C-band Sentinel-1 results showed good agreement with the L-band PALSAR-2 dataset, in which the mean and maximum vertical subsidence rates are −13 and −120 mm/year, respectively. For better visualization of the results, the SBAS InSAR velocity map was down-sampled and principal component analysis (PCA) was performed on ~3600 randomly selected time series of the study area, and the results are presented by two principal components (PC1 and PC2).
Highlights
Since urban growth in recent decades has accelerated on a global scale, migration of the population from rural to urban areas has increased
This study presents the spatiotemporal characteristics of intensity, phase, and coherence of PALSAR-2 L-band images (λ ~24 cm) of the ALOS-2 satellite provided by the Japan Aerospace
Several small baseline subset (SBAS) interferometric synthetic aperture radar (InSAR) time series studies based on different X-band and C-band datasets have been done for NW Iran [45,46,47,48,51]
Summary
Since urban growth in recent decades has accelerated on a global scale, migration of the population from rural to urban areas has increased. Ground subsidence is gradually becoming a major problem for governments and people, especially if not properly planned industrial, mining, and agricultural activities are accelerated [7,8,9,10,11,12,13]. It is a long-term phenomenon in most cases and acts like a “dark death” for the Earth. Important basins in Tehran, Mashhad, Rafsanjan, Yazd, and Neyshabour have fallen victim to ground subsidence due to a lack of underground water recharge, a lack of supervision, and illegal use of natural resources [14,15,16,17,18]
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