## 1 Introduction
In this regard, the widely used complexes of geophysical methods, implemented both in the traditional aerial version and in the ground, usually include magnetic, gamma-survey, and some version of electromagnetic sounding method [18; 19]. However, despite the widespread use of electrical prospecting methods in the ground and traditional aerial versions, the UAV systems for electrical prospecting known on the market are still limited by Very Low Frequency (VLF) [20; 21] and Ground Penetrating Radar (GPR) [22; 23] technologies. Such methods do not provide depths of more than a few meters, a maximum of tens of meters, and VLF methods, which depend on the signal  
Appendix 1 tration depth. Having a set of several frequencies it is possible to calculate the apparent resistivity section [16]. The VLF methods, which first appeared in the ground and airborne versions in the 60 s of the 20 th century [24], use a simple plane wave model in the far zone, and the source of the field in the geological environment is the fields of long-distance radio communication and navigation systems in the range 10-30 kHz, mostly military [25]. This is convenient since there is no need to carry the transmitter loop using the UAV. However, evaluating the rationality of using such methods for our task, one should note significant and at the same time fundamental limitations. With the development of satellite communication systems, VLF-navigation systems are gradually being decommissioned, for example, the Omega system (USA) has not functioned since 1997; two of the five transmitters of the Alpha (USSR) system were turned off in 2014, and the rest are turned on periodically and unpredictably for civil services [26]. As a result, the presence of stations with a good signal level in a specific area, often remote from the infrastructure, and with constant availability for the entire period of geological work, is not guaranteed. In addition, as the number of stations decreases, the available set of frequencies also decreases; it becomes insufficient for frequency inversion. Work on the VLF method in both ground and airborne and UAV versions was mainly carried out at the same frequency, in order to map the distribution of the derivatives of the electrical resistance of the upper part of the section over the area, so the VLF methods played a role electrical profiling operations, not sounding. This is due to the shallow depth of VLF methods--the depth of propagation of electromagnetic waves into the geological environment also depends on the resistance of rocks, with a low resistance, the depth of VLF methods does not exceed 10-20 m, with a high one it can reach 40-50 m [24; 25; 27]. When searching for hidden deposits, this is not enough, and data inversion in exploration cases at such a depth is often meaningless. In this regard, this method does not even theoretically allow solving the problem of sounding to depths of 100 or more meters, but it can be successfully used together with magnetic and gamma surveys at the first stage of geophysical mapping in the variant of electrical profiling operations. In our opinion, this option will be used quite often in the UAV version. It should be noted that the FDEM methods used in the traditional aero or ground version are not limited by only the VLF version, however, in this case, they require heavy generator system on the aircraft and therefore their direct copying to the UAV option is not possible. The TEM methods based on the phenomenon of electromagnetic induction provide significantly greater possibilities for deep sounding. The traditional version of TEM methods is as follows: on the aircraft (or at the operators during ground surveys) there is a generator and a current switch that generates rectangular current pulses of a given duration and then a given pause.