| Popis: |
Electromagnetic (EM) methods of geophysics allow to image the subsurface conductivity distribution by analyzing data measured on the Earth surface. The transient electromagnetic (TEM) sounding method is a time-domain controlled source one which utilize a non-stationary transient process of the EM field decaying in the conductive medium due to the step current excitation which is described by the Heaviside function. The mathematical and algorithmic tools for express analysis of such experimental data acquired for the TEM method are presented in this article, the practical application of which is sometimes important for experimental in field measurements, since it allows as to make immediate decisions on optimization of experimental field work as well as to qualitatively estimate the state of the object under study. The proposed express analysis algorithm is developed on the basis of a widely used transformation of the experimental TEM curve, also known as the S-inversion, which in turn is based on the approximation of a conductive half-space by a thin sheet which is immersing into a non-conductive half-space with the decaying of transient process in the EM field. To reduce the influence of noise into the measured data, we carrying out the approximation of the experimental sounding curves accounting several aspects: the solutions of equations which describe the penetration of EM field into a conducting medium; the function of the cubic spline; and elements of mathematical analysis of continuous functions. According to profile measurements, one dimensional models of resistivity distribution were obtained using the created express analysis tools and a pseudo two dimensional model of the geoelectric cross-section of the waste reservoir dam which is next to the Stebnyk town was constructed on their basis. The analysis of the obtained models allowed us to detect two areas where it is desirable to carry out additional studies to clarify the geological situation. Of course, algorithms for inversion of experimental data, both as from a mathematical point of view as well as from the point of view of algorithm implementation, are much more complicated. However, if one implements a fast and efficient one-dimensional inversion algorithm for the TEM data instead of the transformation mentioned above, it will be possible to significantly improve the reliability of the result. |
