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1 D Forward and Inverse Modeling of DC Resistivity


RESIX is an interactive, graphically oriented, forward and inverse modeling program for interpreting resistivity sounding data in terms of a layered earth (1-D) model. Sounding curves can be entered as a function of a for Wenner or pole-pole soundings, AB/2 for Schlumberger soundings, R for dipole soundings or N for dipole-dipole or pole-dipole soundings.

Sounding curve values are entered as apparent resistivity as a function of spacing. Forward modeling enables you to calculate a synthetic resistivity sounding curve for a model with up to ten plane layers. Resistivity sounding curves are calculated using linear filters.

Shifting of data with overlapping curve segments is handled automatically by shifting the synthetic curve to match the offsets between segments in the data. This is done by assuming the data for the longest spacings is correct and shifting segments at shorter spacings to meet the data at longer spacings. Alternatively, you can shift the data curve itself to meet either the longest or shortest spacing segment. This can be done either automatically or manually in the interactive graphics mode using the Shift Segments option.

Masking of data is achieved in the interactive graphics interpretation module by pointing and clicking on data points. These points can be unmasked or deleted according to the users needs. Masked points do not influence the error or inversion calculations. Interactive model input via the mouse allows the user to see changes in the calculated curve as he enters the model graphically. Graphic entities of the plate output may also be resized and positioned using the mouse.

Inverse modeling allows you to obtain a model that best fits the data in a least squares sense, using ridge regression to interactively adjust the starting model parameters. You can constrain some of the starting model parameters so the inversion will not adjust them. Starting models for inversion can have up to 8 layers. Forward models can have as many as 10 layers. Constants can be applied by fixing (or freezing) a parameter, or by imposing limits on a parameter. Parameters can be resistivity thickness of layers, or resistivity/depth to bottom of layers.

Results from forward or inverse modeling can be directed to a printer or plotter for report ready, hard-copy output. Results can also be saved in a binary random access disk file for later retrieval. Inverse modeling can be carried out in an unattended batch mode. Resix provides several options to present the observed data, the theoretical (forward) data, and the geo-electrical model section used to calculate the forward response. This information can be graphically presented individually on a dot matrix printer, a laser printer, or a pen plotter. You can also print the data and model section in a tabulated, paginated form directly to a text printer.

Data stroage is handled by a new data base file format that holds up to 200 data sets (or sounding curves). This size of the file depends on the number of sounding cureves it contains.

Standard Components

Resix v.3 software and instruction manual.