## 3 Results of Experimental and Real Unmanned Aerial Vehicle (UAV)-Gamma Surveys with Small Detectors
### Case 1. Spectrometric Surveys with Small Scintillation Detectors
Figure 6: Results of gamma survey at the Tazheran site: (**a**) terrestrial survey with the SRP-68 radiometer; (**b**) UAV survey at a height of 25 m with a CsI 100 cm\({}^{3}\) detector (in both cases, classification by quantiles); (c) gamma spectrum of rocks of the area with increased radioactivity, as measured by samples in the laboratory; (**d**) graphs of the gamma field variability on the ground and in the air on three profiles. As can be noted, the information content of radiometric surveys practically does not depend on the volume of the detector or on the direction of flight of the profiles. Geospatial resolution of maps made from the results of surveying with a large crystal is slightly higher, however, all the main anomalies are distinguishable. The same conclusion can be drawn from a comparison of Figure 1a,b. As a result, it can be stated that in the radiometric mode a low-altitude survey with a 6.5 cm\({}^{3}\) CsI (Tf) detector is quite comparable with the terrestrial survey data performed by the NaI (Tf) 15 cc detector with stops. At best, approximately 40 linear km of gamma-radiometric surveys located on the site can be performed in pedestrian  
Figure 7: Comparison of UAV survey results in forward and opposite directions (LPI interpolation, quantile classification): with lightweight detector CsI 6.5 cm\({}^{3}\) (**a,b**); with CsI 100 cm\({}^{3}\) detector (**c,d**). mode in 4 days, while the UAV survey, the area of which is larger, took only three hours, including time to replace batteries. Are the maps of individual radionuclides of the same quality and stability? Looking at the maps of measurements in the potassium channel, only one energy line can be used (1.46 MeV) (Figure 8). It can be seen that, despite the small number of gamma quanta registered by the detector, the main anomalies corresponding to the boundaries of geological structures are coincided. The area of decreased field values in the south-eastern part, and a small 'bridge' separating it from the main anomaly, as well as a very small anomaly of decreased values in the southern corner of the site, continue to be mapped. Between each other, the maps constructed from the results of direct and return flights have a fairly good convergence (Table 3). Regarding the measurement results corresponding to uranium radionuclides (Figure 9), as mentioned in the Methods section, the classical version of field gamma spectrometry uses one energy line (1.76 MeV). In this case, the efficiency of a small scintillation detector is insufficient to register a statistically representative amount of data, two quants per second are recorded at best, and the geostatistical surface is absolutely unstructured (Figure 9a). However, unlike potassium-40, the gamma spectrum of the uranium-radium series has more than one energy line (Figure 9b), and lines with energies of 0.609 MeV and 1.12 MeV are additionally used for processing (Section 2). The probability of effective detection of radiation along these lines with the use of a small-volume scintillation detector is much higher and, due to the low survey altitude, even the 0.609 MeV line has not yet decayed significantly. Using several energy windows, high-quality maps of uranium are obtained (the root mean square error (RMSE) according to the results of ordinary and control surveys does not exceed 12.5%, Table 3), on which the previously noted local structural features of  
Figure 8: Results of gamma spectrometry with CsI 100 cm\({}^{3}\) detector, potassium-40 channel (1.46 eV) (**a**) forward flights; (**b**) flights in the opposite direction. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Dose Rate, 6.5 cm\({}^{3}\)** & **Dose Rate, 100 cm\({}^{3}\)** & **U** & **Th** & **K-40** \\ \hline RMSE, \% & 7.3 & 5.2 & 12.4 & 23.7 & 22.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Root mean square errors of survey based on the results of comparison of survey data performed in the ordinary and reverse directions. the site are clearly visible (Figure 9c,d).