Characterization of saline coastal aquifers using 2-D joint inversion of ERT arrays

Electrical resistivity tomography (ERT) is a well-known geophysical tool for mapping salinity problems, mainly in coastal aquifers. High-resolution ERT images provide essential information for the characterization of these salinity-affected groundwater-bearing zones. Present study centres around salinity affected area of the Manadarmani-Contai region of West Bengal, India, where ERT data was collected using multiple arrays. After data collection, one significant processing step includes the selection of a suitable inversion scheme to generate a more reliable subsurface model. As for different arrays, the same inversion scheme leads to different results depending on the data sensitivity, signal strength, background noise etc. Thus, to overcome this limitation, we have jointly inverted Dipole-Dipole and Wenner arrays. As dipole-dipole has more no. of data points than the Wenner array, Jointly inverted results are slightly biased towards the dipole-dipole array. Although these arrays have different sensitivity patterns, the combination of this joint inversion provides good lateral resolution and shows a saline clay layer about 24 m below in the depth section. Further, Inversion results can be more refined by adopting different norms.