## 3 Results of Experimental and Real Unmanned Aerial Vehicle (UAV)-Gamma Surveys with Small Detectors
### Case 1. Spectrometric Surveys with Small Scintillation Detectors
comparing results of terrestrial radiometric surveys with UAV surveys at different altitudes;  
an empirical study of the gamma-field attenuation from small and not very contrasting objects with height;  
comparative assessment of the efficiency of scintillation detectors of various sizes in UAVs and ground-based versions. This area has a more complex geological structure, it is composed of alternating rock packs of various composition, with a thickness from the first metres to the first hundreds of metres. Part of the area has an aerospace map [14] Figure 11, which cannot be trusted to the same extent as a ground map, but gives some indication of the stratigraphic subdivisions presented here. The rocks in the Olkhon region are generally highly metamorphosed and it is difficult to visually determine their genesis and composition. A priori, the granites of the Shebarta complex are the most radioactive rocks in this area, but their radioactivity is not too high, and the background reaches 10-12 uR/h on the outcrop surface. The model area contains thin layers of rocks of this stratigraphic unit. According to general concepts, anomalies from objects a few meters in size at an altitude of several tens of meters should have already smoothed out so much that detectors of small volume, such as 6.5 cm\({}^{3}\), cannot be used to map them, and this is of interest for research. Figure 11: Scheme of survey profiles at Chernorud site, coordinates in EPSG 28418 (**a**) and aerospace geological map [PERSON] et al., 2013 (**b**,**c**). The map of the survey profiles on the site is shown in Figure 11. The distance between the profiles is 50 m, the flight speed is 20 km/h. The composition and sequence of the studies performed were as follows:  
* First, a pedestrian gamma survey was carried out using an SRP-68 radiometer. * Then the same profiles were surveyed with a lightweight (6.5 cm\({}^{3}\)) radiometer, which allowed evaluating the effectiveness of a much smaller detector in terrestrial mode. * After that, a UAV radiometric survey was carried out with the same lightweight radiometer at two heights of 30 m and 60 m with terrain draping. * Finally, to remove uncertainty over the sufficiency of the efficiency of the lightweight radiometer for surveys at altitude and at a relatively high speed, a UAV survey was carried out with a CsI(Tl) spectrometer with a volume of 100 cm\({}^{3}\), and an integrated (radiometric) channel map was made. This survey was carried out at altitude of 35 m.  
The contours of the areas of the different kinds of survey did not coincide completely. Therefore, in all the figures, the maximum size of the area corresponding to the terrestrial survey is shown for orientation. Surveys with the SRP-68 radiometer played the role of reference data. They were carried out by two teams of 2 people. The accurate topogeodesic network has not been created, the coordinates of the pickets were determined using Garmin navigators. The lightweight radiometer operates in the automatic recording mode with a frequency of 0.5 Hz; there is, thus, no need for operators to stop. Navigation was also carried out using a Global Positioning System (GPS) navigator. Taking into account that the operators of ground survey with various radiometers reached the points using GPS, the ground data has a non-systematic error associated with the measurements of the gamma field at spatially different points. At the same time, the SRP-68 data were linked in the Geographic Information System (GIS) project to the model location of the pickets, and the data of the lightweight radiometer to the real one. With the data obtained, maps and graphs of the gamma field were constructed by profiles (Figures 12-14). Interpolation was performed using the local polynomial method. Figure 12: Examples of raw radiometric data: (**a**) ground survey with a light radiometer; (**b**) UAV survey with a light radiometer at 30 m altitude. Classification of data by quantiles.