A Design Method of the Transmitting Waveform of Electromagnetic Sounding Based on Selective Harmonic Elimination

The exploration target at different depths through the ground-airborne frequency domain electromagnetic method (GAFDEM) is detected by transmitting waveforms at different frequencies. When taking these different depths into detail, arbitrarily distributed frequencies are needed. However, the current transmitting waveforms are mostly in a fixed frequency ratio or frequency difference, which fails to meet the requirements of exploration accuracy and efficiency at the same time. Therefore, as a solution to this problem, this paper proposes a transmitting waveform design method based on selective harmonic eliminated pulse width modulation (SHEPWM) technology. In the SHEPWM method, three transmitting waveforms with the desired spectrum are obtained by directly controlling the switching angles of a binary sequence with an artificial neural network algorithm. Firstly, our study puts forward the basic theories and principles of the full-periodic asymmetric SHEPWM waveform. Secondly, the study, through simulation, realizes the pseudorandom, depth-focused, and layer-identification waveform with different detection depths. Finally, the application of the proposed SHEPWM waveform to the geological survey in Kaili City, Guizhou Province, proves the correctness and feasibility of this proposed method.

Overview of modern hardware and software for near surface electromagnetic sounding in the frequency domain

For the study of the first ten meters of the ground, instruments operating in the frequency domain are most widely used. The compactness, speed of operation, ease of operation of such equipment, as well as the quality of the information obtained, determine its applicability for solving a wide range of issues: from searching for local objects to identifying structural features of the upper part of the section. The article provides an overview of current hardware and software developments for near surface electromagnetic soundings in the frequency domain. A description of all types of non-contact equipment from major world manufacturers is given. The features of both the hardware itself and the approaches to their implementation are described. Methods of primary processing and data inversion are considered. Conclusions are drawn about the need to find new ways to eliminate of equipment deficiencies.

Electromagnetic research in the Altai-Sayan mountain region

A new software-measuring complex has been developed for recording non-stationary electromagnetic soundings based on mobile modules created on the basis of 24-bit ADCs, with built-in GPS receivers, with recorders located directly at the field sensors, arithmetic sampling step and recording of all signal realizations. The deep structure of the Uimon depression in Gorny Altai has been studied based on the time-domain electromagnetic sounding. Research is relevant due to the high seismic hazard of the area, and is also in demand for prospecting and exploration of predicted minerals here. To construct geoelectric models, data from several years of measurements were used, during which more than 60 soundings were performed. At this stage, the interpretation was performed using computer systems within the framework of a horizontally layered model. The interpretation results are presented in the form of sections and threedimensional visualizations, which clearly reflect the structure of the depression. Further, three-dimensional modeling and additional measurements are planned to verify and refine the results obtained.

FIRST RESULTS OF STUDIES IN THE GORLOVSKAYA VALUES BY GROUND METHODS OF ELECTRIC EXPLORATION WITH CONTROLLED SOURCES

The article presents the first results of the study of the Gorlovskaya depression in the area of coal deposits of the Novosibirsk region by methods of ground electrical prospecting using transient electromagnetic sounding and electrical tomography. Near-surface models were obtained to depths of 100 m, as well as deep geoelectric characteristics of the sedimentary filling of the depression and the eastern fault boundary.

FORECAST OF GAS HYDRATE ACCUMULATION IN MEZSOZOIC SEDIMENTS OF CENTRAL YAKUTIA FCCJRDING TO ELECTROMAGNETIC SOUNDING DATA

This article discusses the results of electromagnetic studies by the TEM method. They are made within the limits of Central Yakutia. The purpose of the research is to study the features of the geoelectric structure of the upper part of the section. The upper part of the cryolithozone was studied, its geoelectric characteristics were determined, talik zones were identified, as well as zones promising for detecting gas hydrate accumulations.

Lightweight Unmanned Aerial System for Time-Domain Electromagnetic Prospecting—The Next Stage in Applied UAV-Geophysics

Nowadays in solving geological problems, the technologies of UAV-geophysics, primarily magnetic and gamma surveys, are being increasingly used. However, for the formation of the classical triad of airborne geophysics methods in the UAV version, there was not enough technology for UAV-electromagnetic sounding, which would allow studying the geological environment at depths of tens and hundreds of meters with high detail. This article describes apparently the first technology of UAV-electromagnetic sounding in the time domain (TDEM, TEM), implemented as an unmanned system based on a light multi-rotor UAV. A measuring system with an inductive sensor—an analogue of a 20 × 20 or 50 × 50 m receiving loop is towed by a UAV, and a galvanically grounded power transmitter is on the ground and connected to a pulse generator. The survey is carried out along a network of parallel lines at low altitude with a terrain draping at a speed of 7–8 m/s, the maximum distance of the UAV’s departure from the transmitter line can reach several kilometers, thus the created technology is optimal for performing detailed areal electromagnetic soundings in areas of several square kilometers. The results of the use of the unmanned system (UAS) in real conditions of the mountainous regions of Eastern Siberia are presented. Based on the obtained data, the sensitivity of the system was simulated and it was shown that the developed technology allows one to collect informative data and create geophysical sections and maps of electrical resistivity in various geological situations. According to the authors, the emergence of UAV-TEM systems in the near future will significantly affect the practice of geophysical work, as it was earlier with UAV-magnetic prospecting and gamma-ray survey.