GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 3.2 665 between low and high resistivity zones. The second synthetic example (SIN2, Fig. 2a) is taken from Sen and Stoffa (1995) and it is a more complex model where a shallow layer (thickness 1.2 m) having a resistivity of 50 Ωm is superimposed to a medium, split into a left conductive zone (10 Ωm) and a more resistive (100 Ωm) right part. The ERT line consists of 16 electrodes spaced 1 m apart where a dipole- dipole array is used with a max =1 and n max =11 (77 measurements). Inversion is carried out using the same inversion parameters of SIN1 case, but increasing the cell size for global inversion in order to reduce the computational time. Results show a good convergence of both methods to the percentage noise added, with a more accurate reconstruction of the sharp interface achieved by VFSA (Fig. 2c), even though using a smaller number of model parameters. Fig. 1 - (a) Synthetic model SIN1. (b) Gauss-Newton inversion. (c) VFSA inversion. (d) RMSE vs. number of iterations. Fig. 2 - (a) Synthetic model SIN2. (b) Gauss-Newton inversion. (c) VFSA inversion. (d) RMSE vs. number of iterations.