The Relationship Between the Variations in the Low-frequency (0.1–10 Hz) Near-zone Electromagnetic Field of a Controlled Source and the State of the Ionosphere

Based on the experimental studies on measuring the controlled source signals in the near zone under different geophysical conditions, it is established that the amplitude of the field experiences variations in the lower part of the ELF band and at lower frequencies. At the same time, variations in the VLF range are absent. For identifying the factors responsible for this peculiarity in the behavior of the field, excitation of the ELF and lower frequency electromagnetic field in the Earth-ionosphere waveguide with different conductivities of the Earth and the ionosphere is considered. The theoretical calculations are proposed showing that at low conductivity of the Earth, the effect of the ionosphere in the near zone can be significant.