Document Type : Research Paper
Authors
1 scientific staff, Soil conservation and water management institute
2 Geology department, University of Isfahan
Abstract
In this study the Sentinel-1 satellite data (ascending, descending, and combined modes) and PSInSAR technique were utilized to assess and map land subsidence risk in major watersheds of Isfahan Province, including Isfahan-Borkhar, Najafabad, Northern Mahyar, Southern Mahyar, and Kuhpayeh-Sejzi. The Sentinel-1 radar data (2014 to 2023) were used, including ascending and descending imagery, to resolve displacement ambiguities caused by directional movement. Initial data processing involved co-registration of radar images to align pixels accurately and generate interferograms for phase change extraction. Persistent scatterers (PS) were identified using the Amplitude Dispersion Index (ADI) and phase stability analysis. Atmospheric and orbital errors were corrected using statistical models and inversion techniques to eliminate biases. Temporal analysis of ground displacement was conducted to calculate deformation trends, with data georeferenced for spatial interpretation. Validation was carried out by comparing results with ground-based data and independent sources. Final outputs included cumulative subsidence maps, annual subsidence rates, and risk zoning maps highlighting areas prone to land subsidence. The findings reveal that subsidence in the study area ranged from negligible to 55 cm over the nine-year observation period. Annual subsidence rates in parts of the Isfahan-Borkhar and Southern Mahyar watersheds reached 60 mm per year. Combining ascending and descending data improved accuracy and enabled the separation of vertical and horizontal displacement components. The highest cumulative subsidence was observed in urban and agricultural zones of Isfahan-Borkhar and in clayey sediment areas within Southern Mahyar. Hazard zoning maps indicate that Isfahan-Borkhar and Southern Mahyar watersheds have the largest areas classified as high-risk. Other watersheds predominantly exhibit moderate to low-hazard zones. The maps demonstrate a strong correlation between severe subsidence and land use (urban and agricultural areas) as well as geological features. Future research should focus on continuous monitoring and the development of predictive subsidence models to address this issue effectively.
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