Microwave D-InSAR technique for assessment of land subsidence in Kolkata city, India

An effective microwave Differential Interferometric Synthetic Aperture Radar (D-InSAR) technique was used to rapidly assess the potential land subsidence with high precision by exploiting the phase difference of two temporally separated SAR data in the region of Kolkata city, India. The objective of this study is to assess land subsidence using D-InSAR technique and to delineate the regions of land subsidence caused by over exploitation of groundwater by minimising the errors by applying topographic and atmospheric corrections. The study area forms a part of Indo-Gangetic plain. Three ENVISAT Advanced Synthetic Aperture Radar (ASAR) images of the years 2003, 2007 and 2010 were acquired to study the temporal evolution of land subsidence in the study area. The phase changes due to topography in the interferograms were removed by using Shuttle Radar Topography Mission (SRTM) degital elevation model data. Medium Spectral Resolution Imaging Spectrometer (MERIS) data were applied to remove the atmospheric noise in the interferogram. The deformation fringes were observed in the northern and central part of the study area where the land subsidence was 12 and 18 mm during the years of 2003–2007 and 2007–2010. The regional variation in the piezometric head compares well with the fringes of the interferogram. This confirms over extraction of groundwater is the main cause for land subsidence in this region. Hence, it is necessary to reduce groundwater pumping and to augment rainfall recharge in northern part of the study area.