The model window is where you control the dimensions and type of your sounding, the spacing of electrodes, and enter your observations. This also displays the predicted apparent resistivities from the model and the EM31 reading that would result from measuring this model from a height of 1 m (with a properly calibrated unit).
The topmost part of the window shows the values of the number of spacings , the first spacing, the type of sounding, and the spacings per decade. A message area is also present at the right side of the upper part of the window that usually tells whether the current model was used to calculate the values shown. At present the spacings per decade is fixed at 6. Wenner and Schlumberger soundings can be chosen from the popup menu at upper right. The number of spacings may not exceed 19. The first spacing is the distance between electrodes (a) as shown in the text; this is the distance between electrodes for the Wenner array. Note that log of spacings are assumed to be evenly distributed, so the first six spacings are 1.00, 1.47, 2.15, 3.16, 4.64, and 6.81 times the first spacing.
The list box with layers listed allows editing the thickness of a layer and its resistivity. For changes to the model to affect the calculated values in the bottom of the window and to be displayed in the Plot Window, you have to click on the Calculate from Model button.
Layers can be added or removed using the Add Layer or Delete Layer buttons.
Clciking on the Calculate from model button will cause the program to use the current model in the layers listbox to compute apparent resistivities at all electrode spacings and determine the RMS misfit compared to observations; this is reported in the upper right part of the window.
The Invert Data button will start an inversion of the data entered for the sounding. As this is an iterative inversion, it depends rather strongly upon the starting model, hence it is wise to try some forward models (by adjusting the model in the Layers listbox and the pressing the Calculate from model button) before inverting. The inversion will continue to iterate until it either iterates to the maximum number of iterations set in the Preferences Window or the RMS misfit falls below the threshold set in the Preferences Window.
The bottom list gives the electrode spacing, the observed apparent resistivity, and the apparent resistivity computed for the model.
The model can be saved to a file (Save Model... menu item from the File menu) or copied to the clipboard (with the observed values). The data is saved separately using the Save Data... menuitem from the File menu.