Radiomagnetotellurics (RMT) is an electromagnetic method that uses signals
from radio transmitters broadcasting in the 10 kHz to 1 MHz frequency range.
Due to its limited frequency range, RMT is commonly used as a shallow-depth
investigation tool. However, in remote areas, there is a lack of radio transmitters
and only signals from very low frequency (VLF) antennas (10–30 kHz frequency
range) can be measured. This can give rise to low signal-to-noise ratio. To overcome this disadvantage of RMT, a controlled-source RMT (CSRMT) can be
applied to measure signals of the low-frequency (LF) and mid-frequency ranges
(30–1000 kHz). Moreover, the wider frequency range of the CSRMT method
(down to 1 kHz) leads to a deeper sounding depth.We present the first RMT and
CSRMT validation studies using two perpendicularly located horizontal electric
dipoles to realize a 3D inversion of CSRMT data.The survey area in Alexandrova
village in Kaluga region, Russia, a previously investigated area, was selected
for a validation study. We acquired the data along 8 profiles with 175 stations.
Transmitter lines for the CSRMT case were about 900 m long, and the minimum
and maximum distances of the stations from transmitters were 450–1000 m,
respectively.We applied 2D and 3D inversions over the far-field data and compared with the previous results. The available geophysical information as well as the borehole data indicate a high agreement between the obtained models and the geological structure.We can confirm that the CSRMT method is a reliable approach for near-surface explorations and that, the existing advanced and tested inversion tools for magnetotellurics, can be used to invert the RMT and far-field zone CSRMT data leading to comparable results.