## 3 Results of Experimental and Real Unmanned Aerial Vehicle (UAV)-Gamma Surveys with Small Detectors
### Case 1. Spectrometric Surveys with Small Scintillation Detectors
Moreover, the resulting map is more detailed than the potassium-40 map, which is built along just one energy line. Similarly to uranium, but using two lines 0.91 and 2.62 MeV, Thorium maps were created (Figure 10). The statistical representativeness of the data and, accordingly, the quality of the surface are worse (RMSE -24%). However, the main anomalies and geological boundaries are still mapped reliably, and the local ones are acceptable. Figure 9: Results of gamma-spectrometry with a CsI 100 cm\({}^{3}\) detector, Uranium series, LPI interpolation, quantile classification: (**a**) poor quality field map based on data of one 1.76 MeV energy line; (**b**) a gamma spectrum of the uranium series; (**c**) field map obtained by integrating lines 0.609, 1.12, 1.76 MeV, flights in the forward direction; (**d**) integration of lines 0.609, 1.12, 1.76 MeV, flights in the opposite direction. It is estimated that the root mean square errors of radiometric and spectrometric surveys as the difference between the values of the cells of the digital field models obtained from the results of ordinary and control (opposite direction) measurements, divided by the values of one of the field's digital model (Table 3). Undoubtedly, the metrological characteristics in spectrometric modes achieved are inferior to large airborne gamma spectrometers for manned aircraft. However, this does not mean that the data obtained are not informative from a geological point of view. On the contrary, this case provides convincing evidence in favour of the practical applicability of low-altitude UAV aerial gamma surveys with small detectors using the described method. Unlike other geophysical fields, for example magnetic or gravity fields, radioactive decay and, accordingly, intensity of gamma field, have a probabilistic nature. For example, the margin of error for serial radiometric equipment is usually 15% (according to Ra-226). Therefore, in real geological prospecting tasks, there is no need to fight for ideal metrology, but it is necessary to analyse the resulting maps from the point of view of their correctness, stability and information content, which in this case is provided. Moreover, the data obtained are quantitative, and the radiometric data and the uranium channel are highly accurate. It should also be borne in mind that the experimental work was carried out in conditions of non-high radioactivity of rocks, the Bruker S1 Titan XRF analyser, which has detection limits for uranium and thorium from several grams per ton, could not determine the concentration of these radionuclides in the samples which were selected for spectrometry (Figure 6c). For example, in geological situations of uranium ore regions, where the typical contrast of gamma background anomalies, even at a significantly higher altitude, exceeds 7 times [9], compared to 2-2.5 as in this model area, the stability and information content of geostatistical surfaces will be much better. Unfortunately, in 2020, it was not possible to conduct experiments on reference deposits of this type, due to quarantine measures, or visiting the deposits was completely prohibited. _Case 2. Comparison of Terrestrial and Different-Altitude UAV-Radiometric Surveys with Scintillation Detectors of Various Volumes_  
On the second model site \"Chernorud\" (Figure 4), located in the area of the educational geological site of the Irkutsk Technical University, a slightly different set of experiments was carried out, aimed at:  
Figure 10: Results of gamma-spectrometry with a CsI detector 100 cm\({}^{3}\), Thorium series, LPI interpolation, quantile classification: (**a**) map obtained by integrating 0.91 and 2.62 MeV lines, flights in the forward direction; (**b**) integration of lines 0.91 and 2.62 MeV, flights in the opposite direction.