## 4 Survey Technique and Data Preprocessing
Classical land surveys with line-to-line arrays were carried out in the geometry of the mean gradient, only in the central third of the length of the transmitter line, and at a similar distance from it. This was very irrational, but it was done to simplify data processing. However, the Mars1D inversion environment allows modeling and taking into account the induction effects from the transmitter. It allowed us to perform a survey of the full length of the line and even beyond it, but at a distance of the first hundred meters from the ground points, the influence of the electrical grounding of the transmitter was too significant. It was possible to perform the UAV-TEM outside the ends of the line, but this further complicated the processing, and since there were no data confirming this position in this article, let us dwell  
Figure 9: Substantiation of the possibility of data processing at a distance from the transmitter line (observed and model sounding curves at the ends of the orthogonal profiles and the level of the recorded signal). on the fact that the maximum survey line length for the UAV-TEM was slightly less than the length of the transmitter line. Based on the survey results, an inversion was performed in the class of 1D-models and geophysical sections were built according to the electrical resistivity parameter (Figures 10 and 11). In addition to the sections and to substantiate the correctness of the solution of the inverse problem, measured and fitted curves for the characteristic sections of the section are given with an estimate of their convergence. It is important to note that the Mars1D software package does not allow one to take into account the inductive characteristic of the sensor and the shape of the current decay in the transmitter line after the pulse is off during modeling. Mars1D was developed for a line-to-line array with an emphasis on working with late times, when the effects of induced polarization, and therefore the early times were not taken into account in processing and the recorded time range was small--on average from 50 to 140 \(\upmu\)s. Despite this, as well as the small number of points on the transient curve, suitable data for processing and inversion were obtained, and even characterized by a fairly good convergence of the observed and model curves fitted as a result of inversion (Figures 10b and 11b). Figure 10: 1D-inversion results of the UAV-TEM data on the survey lines No. 6,5,4 (north of the transmitter line): (**a**) geophysical crossections (electrical resistance); (**b**) convergence of ordinary and model sounding curves. The obtained sections allowed us to draw the following conclusions about the geological situation at the area. As expected, in the eastern part of the area, the sandstone cover most likely began to appear only on the northernmost survey lines and its thickness is insignificant. On the other hand, at this edge of the area, an anomaly was noticeable, typical for dislocation with a break in continuity (profiles 0 points 45-54, and profile 4, points 49-54) of the sub latitudinal direction. It should also appear on the \(-1\) survey line, but the eastern part (points 49-54) of this survey line fell on the area after the UAV's turn, and therefore the data in this place were discarded. However, at the last good measurement point (48), there iwas also a tendency for the resistance to decrease. On the geological map, a little to the south of the area, a tectonic disturbance that is suitable in the direction is noted, which was not traced to the boundaries of the area, but most likely was actually present. Another element, which can be interpreted as discontinuous tectonics, but of a significantly lesser thickness, was noticeable on survey lines 5 (points 42-43) and 6 (points 41-43), located to the north of the transmitter line.