## 3 Developed Drone System for TEM
### Aeromobile Part  
#### 3.1.1 Measuring System  
First of all, it was necessary to create a compact and lightweight measuring system for towing by a light UAV, which makes it possible to carry out surveys by the TEM method. The measuring system consists of an induction sensor, a measuring unit, and a recorder. Instead of receiving loop induction sensors are used--analogs of loops with dimensions \(50\times 50\) and \(20\times 20\) m. These and similar sensors can be used as part of systems for ground-based TEM imaging. Structurally, the sensors are rigid square frames less than \(1\times 1\) m in size, and have the following characteristics (Table 1). The mass of sensors is quite large for light UAVs, but in the future, due to the use of lightweight modern materials and the housing of the meter unit, it can be reduced by 1-1.2 kg without any problems. Depending on the geological task (high detail in the upper part of the section or depth), you can choose one of two sensors. For towing and stabilization of the sensor in flight, a suspension system was developed (Figure 3), which prevented it from twisting around its axis, dampened jerks and vibrations, and also ensured the horizontal position of the induction sensor at the UAV's cruising speed. The suspension design was empirically developed as a result of two months of testing and improvement of several options. The length was 5 m. The sensor was mounted on three semi-rigid braces of various lengths to the central platform where the meter unit, recorder with GNSS antenna, and batteries for powering the measuring system are located. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Title 1** & **Sensor 1*** & **Sensor 2** \\ \hline Equivalent loop dimensions & \(50\times 50\) & \(20\times 20\) \\ Weight, kg & 5 & 4 \\ Measuring depth range, m & 20–500 & 10–100 \\ Measurement start time, \(\mu\)s & 50 & 10 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristics of sensors for UAV-TEM. Figure 3: Unmanned system SibGIS UAS in the version for electromagnetic soundings: (**a**) in flight; (**b**) during takeoff. The weight of the suspension was about 1 kg and could be reduced by at least 200 g due to the use of lighter and thinner structural elements. The meter unit used in all works in 2020 was borrowed almost unchanged from the MARS complex developed by the authors, designed for ground-based surveying by the method of electromagnetic sounding and induced polarization (EMS-IP). It is a block of four (for a four-channel meter) independent successive approximation analog-to-digital converters (ADCs) with parameters 100 kHz/18 bits. It is possible to record data simultaneously on all channels with different gains, which will increase the dynamic range of the recorded signal. The block weighs about 600 g. This weight will be reduced by half by changing the metal case and durable connectors. Surveying by the EMS-IP method is performed in start-stop mode, not in continuous mode, in line-line geometry with galvanic ground, and is focused to work with induced polarization effects. In this regard, this ADC and current switch was a number of disadvantages in terms of using for UAV-TEM. First, in the existing version of the ADC unit, continuous measurement was not implemented, and half of time spent to save the measurement. This led to a twofold decrease in the received data per unit of time, which is very important for a fast-moving UAV system. Secondly, the firmware of the ADC and power unit assumed the recording of rather long time intervals, since the IP effects appear at the late times of the secondary EMF decay. For methods without galvanic grounding, including UAV-TEM, recording of later times is completely useless, since the signal decay rate is much higher, and it makes no sense to record noise.