Run Sensitivity

By clicking with the right mouse button on the main node of the “ERT Data” and selecting “Run Sensitivity” will open the window shown in Figure 327.

_images/fig_c0oxi5.png — Figure 326 Run Sensitivity

_images/fig_p07g7i.png — Figure 327 Run Sensitivity Panel

The window has two tabs: Sensitivity and Forward Solver Setup. The latter is already explained in the section Run Forward Model. In the Sensitivity panels it is possible to set the number of quadrupoles on which to compute the sensitivity. The sensitivity is an index of how much a change in resistivity of the soil affects the measurement of the potential as the two parameters are directly proportional. The user can compute the sensitivity of a specific quadrupole or of all quadrupoles together.

_images/fig_aiaguo.png — Figure 328 Sensitivity panel

In the first case, uncheck the “All Quadrupoles” box and type the number of the quadrupoles in the appropriate number box (1 in Figure 328).

The Abs check box lets the user choose to consider the positive and negative values, or only the absolute values. If more than one quadrupole is specified then the Abs mode is automatically enabled and it is not possible to uncheck it to avoid errors in the sensitivity. This because the sum of positive and negative superimposed areas, resulting from different quadrupoles, can lead to uncorrected values of the final sensitivity.

The sensitivity can be computer in term of V/I or in term of the Apparent Resistivity, so set “Use K” disabled in the first case, and enabled in the second case.

The sensitivity can be computed on all the quadrupoles, or only on the filtered list, so use the flag “Ignore skipped quadrupoles” to select the desired configuration.

For advanced needs, it is also possible to enable “Save node potentials” to let be saved in the temporary folder used during the later computation a text file with the potential for each node of the mesh.

Clicking on the Run Sensitivity button will start the process. A progress message and a Process Completed message will appear during and at the end of the calculation (Figure 329).

_images/fig_oreax8.png — Figure 329 Sensitivity Model computation

The results can be visualized using the “Sensitivity Model” option (sub-node of Mesh and Model option, section Sensitivity Model). In the example in Figure 330, a full quadrupoles sensitivity is calculated and visualized trough sections and volumes. As expected, the maximum sensitivity is in proximity of the electrodes.