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Resix IP2DI (version 4)

2 Dimensional Resistivity & Induced Polarization Polygon Modeling & Inversion


RESIX IP2DI is a finite element forward and inverse modeling program that calculates the IP and resistivity responses of two-dimensional earth models. The model is composed of closed bodies, layers, or both which are automatically mapped onto the finite element mesh. RESIX IP2DI outputs the data as contoured pseudosections or profiles. Batch mode calculations, interactive graphical model construction, and control of the mesh assist you to produce quality finite element models. Now includes 256 colour support for both screen and hardcopy graphics.

RESIX IP2DI v4 is written in Fortran 90, using a protected mode compiler and is now a single executable module. Previous limitations on size of data sets and grids no longer exist, because the space needed to store the pseudosection data, synthetic results and the finite element grid are dynamically allocated to accommodate the data to be interpreted. In addition, the virtual memory allows the user's hard disk to be used for storage if actual RAM is not available. The result is that arrays with hundreds or even thousands of electrodes and with very large n-values can be accommodated. The supported arrays are: Wenner, Gradient, Pole-Dipole, Pole-Pole, and Dipole-Dipole.

RESIX IP2DI calculates the theoretical response using the isoparametric finite element method developed by Luiz Rijo (1977). This Ph.D. thesis (Modeling of Electric and Electromagnetic Data, 7-88,155) is available through University Microfilms International of Ann Arbor, Michigan.

RESIX IP2DI uses Inman-style ridge regression inversion of polygon-based 2-D models to best fit the 2-D pseudosection data in a least squares sense. Up to 200 model parameters can be selected from body resistivities and IP parameters and from the x- and z-position of each vertex. In addition, groups of vertices can be locked together to form a single unit whose x- and/or z-position can be used as an inversion parameter. This inversion is different from other methods currently being used in that it requires that the user construct a geological model using the mouse by creating polygons of constant resistivity and IP value. The inversion is used to automatically improve the fit of the model by automatically adjusting some model parameters.

This inversion is a genuine 2-D inversion of 2-D pseudosection data that allows the user to select which parameters to vary and which parameters to freeze. By default, all parameters are frozen; the user interactively selects those parameters to be used in the inversion using the mouse during model construction. The 2-D models can be constructed as a combination of up to 100 bodies and layers and up to 1000 vertices per model.

Data can be imported from any Syscal series receivers and ASCII formats.

In addition to the forward and inverse calculations the Field or synthetic data can be compared to analytic results from layered earth models or quarter space models.

Models are constructed using an interactive graphics screen that allows two user-selectable pseudosections to be displayed above model construct area. A third pseudosection can be displayed as a colour filled background to the model.

Topography corrections are done by calculating a 1ohm-m homogenous earth model (including topography) for the resistivity values only. The field data is then divided by these calculated values to obtain the corrected data.

The finite element grid is determined from the number of electrodes and the electrode spacing. The package automatically creates a fine grid for models with a topographic relief and assigns a very high resistivity value for air. The grid can be edited using the mouse. Vertical and horizontal elements can be inserted or deleted and elements can be split in half by using the mouse.

RESIX IP2DI supports 256 colour graphics display on screen as well as hardcopy. Two colour rasterizers are incorporated for hardcopy to support most commercial colour and monochrome devices.

Standard Components

RESIX IP2DI v4 software and manual.