OPTIMIZATION OF CALCULATION ALGORITHM OF ELECTRICAL RESISTIVITY TEMPORAL VARIATIONS BY THE VES MONITORING DATA FOR INCREASING ACCURACY AND RELIABILITY OF RESULTS
Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences
Journal: Science and technological developments
UDK: 550.837.311 + 550.8.056
Keywords: geoelectric structure, horizontally layered model, vertical electrical sounding, multi-electrode array, precision geoelectric monitoring, inverse problem solution, electrical resistivity, temporal variations, optimization of calculation methods
Аnnotation: The authors are developing a method for precision monitoring of specific apparent electrical resistances of individual layers of the earth's crust. This task is extremely difficult, since apparent resistances are actually observed, and then it is necessary to solve a whole complex of complex problems of processing them: removing noise, isolating physically determined components and, most importantly, solving the inverse problem of reconstructing resistivity from measured values of apparent resistance. The purpose of the work is to improve the methodological foundations of precision monitoring to increase its accuracy. The data processing algorithm is divided into a sequence of elementary operations: data aggregation, time series smoothing, noise filtering, estimation of seasonal (exogenous) effects, solving the inverse VES problem. The solution of the inverse problem is a substantially nonlinear operation, and all the others become non-linear if there are data gaps in the signal, which is practically inevitable during long-term observations. Therefore, the final result can significantly depend not only on the settings of individual operations (width and/or type of weight function of the aggregation/smoothing window, etc.), but also on the order in which these operations are performed. In the work, by the method of numerical experiment on real data it is estimated how strongly the sequence of the above operations affects the result. For the calculations, unique data of long-term precision monitoring by the VES method were used. It is shown that the smoothing operator can be applied to both apparent and specific resistivities - this almost does not affect the result. The order of seasonal filtering and solving the inverse problem, on the contrary, is important. It is shown that error estimates for the calculation of specific resistance based on the internal convergence of the algorithm for solving the inverse problem are unacceptable, since they differ by two orders of magnitude from the real errors. For reliable monitoring of temporary variations in resistivity in the deep layers of the structure under investigation, it is necessary to increase the stability of the selection of resistivities according to a given VES curve, as well as take other measures to optimize the algorithm.