ZOND

Specialized software ZondCHT is designed for two-dimensional data interpretation of cross-boreholes electrical resistivity and induced polarization tomography data.

The program allows solve a 2.5-dimensional forward and inverse problem. The term “2.5” means that the geological section is two-dimensional and the field of the source is three-dimensional.

Electrical tomography is a whole technique including both the method of field observations and technology of processing and field data interpretation. Its feature is multiple reusing as a source and receiver just the same electrodes position, fixed on a profile line.

Such approach allows from one hand to work with a modern high-performance instruments, and on the other hand, to apply effective algorithms of modeling and inversion. For interpretation of electrical tomography data is used two- and three-dimensional models. It significantly extends the range of electric prospecting solved problems due to sections investigating that are considerably different from «classic» horizontal-stratified.

Resolution and thus interpretation of quality electrical tomography is closely connected with the number and density of measurements on one site. Their number usually reaches first thousand that is why the question on field measurement efficiency has basic importance and in many aspects defines possibility of practical use of this method. Special equipment with programmed automatic switching of electrodes is applied for reaching of maximum effectiveness of field works.

In differ of land survey where resolution (possibility to determine the object) rapidly decreases with depth, in cross-borehole electrical tomography sensitivity of system smoothly decreases with distance from borehole. It allows call cross-borehole electrical tomography – high-resolution electric prospecting method.

Taking into account that at each position of the source the certain part of the section influences on results of measurements in a greater degree, we can say that at a successful choice of observation system (number of measurements, a spacing between electrodes of cable, electrodes array) it is possible very detailed estimation of parameters distribution in cross-borehole space. The software-hardware-methodical complex for processing of cross boreholes works essentially differs from the land analog. It requires completely switched equipment, the hydro isolated cables and special software.

The program is developed specially for work with boreholes data and includes a range of the unique features distinguishing it from the other programs of ZondRes line, major of them are:

• Support of any boreholes number
• Grid construction according to geometry of borehole
• Different variants of separate data representation
• Special algorithm of pseudo-section calculation
• Use of special inversion algorithms suppressing influence near-borehole space
• Use of special robust schemes of noise estimation

ZondCHT represents ready solution for cross-borehole electrical tomography and solves wide range of problems from mathematical modeling and sensitivity analysis to processing and interpretation of field data. Convenient interface and wide opportunities of data presentation allow solve given geological problem with maximum effectiveness.

ZondCHT uses simple and clear data format that allows combine easily various system of observation. Well-known data formats are also supported.

Program works with any, applied in cross-borehole electrical tomography, types of arrays (two, three and four – electrodes) or their combinations. Using of the mixed systems such as surface-borehole, borehole – borehole, surface – surface is possible.

Important stage that previous field measurement is mathematical modeling of geoelectric structure of work site. Modeling gives chance to estimate the level of the signal and to make a choice of optimum parameters of the observation system for decision of the set geological problem. ZondCHT has great range of tools for mathematical modeling and analysis of fields sensitivity of DC and induced polarization.

As the general task of the software is inversion for geoelectric section parameters – some variants of inverse problem decision are realized in ZondCHT; basic of them are: smoothing inversion – to get smooth, and focusing – for get piece-smoothed distribution of geoelectric parameters vs depth.

While developing of software special attention was paid to a priori data accounting. Because of equivalence of inverse geophysical problems, quality of the obtained results strongly depends on the amount of a priori used data. In ZondCHT there is possibility of weights setting for measurements, fixing and limits making of changing features of different cells, using of a priori model as reference in inversion. The robust schemas of noise estimation are realized in the program. There is also possibility to import and display results of measurements by other methods and cross-boreholes data that improve interpretation results.