Exploring Sentinel-1 for Coastal subsidence monitoring along India’s Gujarat shore using MT-InSAR Technique

India’s long 7500 km coastline covers vast habitats of rich biodiversity and occupants of about 26% of the country’s population in the coastal zone. By 2060, about 60 million of India’s coastal population will be exposed to a low-elevation coastal zone (LECZ) due to global mean sea level rise (GMSL) and its associated hazards (Neumann et al., 2015). However, the low-lying coastal zones are vulnerable to increasing sea levels and coastal subsidence, which threaten the region's socio-economic development (Shirzaei et al., 2021). The erosion assessment report depicts that 60% of the Gujarat shore covering 1600 km of extensive coastline in western India is undergoing erosion. This study investigates and analyzes the combined influence of coastal subsidence and SLR along the south of Gujarat shoreline. In that context, we explored the descending track (path 34) of C-band Sentinel-1 satellite data (92 SAR imageries) in interferometric wide swath mode (IW2 and IW3) of the European Space Agency (ESA) covering the study area from March 2020 to June 2023. The data sets were processed in an open-source GMTSAR software following an advanced Small BAseline Subset (SBAS) based Multi-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR) technique (Berardino et al., 2002). The results exhibit a deformation rate of  >5 mm/year in various parts of Gujarat's Surat, Bhavnagar, and Bharuch districts. Kododara region in Surat district shows a maximum deformation of >15 mm/year, Navamadhiya in Bhavnagar district is showing subsidence of >20 mm/year, and Chanchvel village in Bharuch is also showing subsidence of >15 mm/year. However, the precipitation data shows a total deviation of -3 % and -5 % in the monthly average compared to normal rainfall observed in Bharuch and Surat districts, respectively, from January 2000 to November 2023 (WRIS, India). Rapid urbanization, dependency on groundwater for basic needs and industrialization, and the impact of increasing sea levels could influence the coastal deformation and inundation hazard risk over the long shorelines and those coastal cities, which needs to be investigated in detail.

References

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• Neumann, B., et al. (2015). "Future coastal population growth and exposure to sea-level rise and coastal flooding-a global assessment." PloS one 10(3): e0118571.
• Shirzaei, M., et al. (2021). "Measuring, modelling and projecting coastal land subsidence." Nature Reviews Earth, Environment 2(1): 40-58.