Run Forward Model

By clicking with the right mouse button on the main node of the “ERT Data” and selecting “Run Forward Model” opens a new window for the forward modelling.

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Figure 322 Forward Model

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Figure 323 Forward Model Panel

In this window the user can set the boundary conditions and the solver parameter for the forwards model. To define the area under investigation, the half-space domain is delimited with artificial boundaries that simulate planes in horizontal and vertical direction as infinitely distant. The values for these borders “infinitely distant” (-X, +X, -Y, +Y, -Z, +Z) can be specified using the dedicated selection boxes:

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Figure 324 Choice of boundary conditions

  • Dirichlet condition, in which the potential is known and set equal to zero: V=0. This is the typical condition of an “infinite” half-space in which the potential decreases to zero as the distance from the electrodes increases.

  • Neumann condition, in which the current flow is zero (derivative of the potential equal to zero): \({\partial}\) V / \({\partial}\) \({\eta}\) =0, with \({\eta}\) equal to z for the bottom edge or equal to x for the lateral ones. In particular, this condition occurs at the air-ground interface, because the conductivity of the air is almost zero and in all those cases in which the half space is abruptly interrupted in one direction (vertical walls, big topographical jumps, etc.)

  • Mixed Condition, the Dirichlet condition may lead to values of the potential being underestimated (at a certain distance from the sources), while the Neumann Condition may lead to an overestimation.

In this case it can be useful to use a Mixed boundary condition. It the case of having a remote pole, which is typically close to the outer edges of the mesh, the potential is still not zero at the boundary.

By default, the boundaries of all directions are set to Mixed condition.

In the same panel it is possible to set other parameters as shown in Figure 325

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Figure 325 Forward solver setup panel

SORCG Iterative Solver Parameters:

  • Maximum Number of iterations: when the number of conjugate gradient iterations exceeds this value, the computation stops: the forward modelling solution does not get the convergence within the requested tolerance for the modelled electrode.

  • Omega (SQR preconditioning): this is the value of the conjugate gradient preconditioner in the forward modelling solution. Users can ignore this parameter.

  • Tolerance: this is the value of tolerance requested in the iterative conjugate gradient forward modelling solution.

Modelled Source:

  • Skip TX electrodes with no RX: by checking this command the TX electrodes will be skipped during calculation in the finite elements modelling to get faster runs during forward modelling-only tasks.

Other Parameters:

  • IP Modelling: with ERTLab Studio it is possible to invert Electrical Resistivity (Rho) and Induced Polarization (IP) models at the same time. To include the IP data in the inversion process, check this IP box.

  • CPU Core Numbers: this value depends by the computer hardware features on which you are working. The more threads can be used for the inversion the faster the processing will be running.

  • Temporary Processing Files: it lets to choose where to save the folder with the temporary files of the intermediate steps of the inversion process.

When all the parameters are manually set or automatically calculated by pressing the Compute Optimal Values button, click on Run Forward Model to start the process.

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