## 4 Discussion about the Prospects of Integrated UAV-Geophysical Surveys  
The results of the experimental surveys demonstrate the possibility of obtaining geologically significant results using small scintillation detectors. One of the practical consequences of this conclusion is the possibility of effective integration of gamma-ray surveys with other types of geophysical survey, even simultaneously on one UAV, since a small additional payload mass (spectrometer or radiometer) insignificantly increases  
Figure 15: SibGIS UAS in the version for integrated magnetic and spectrometric survey (**a,b**); and examples of integrated survey results: local magnetic field component (**c**) and map of the uranium channel (integration of 0.609, 1.12, 1.76 MeV lines) (**d**). Kriging interpolation for magnetic surveys and LPI for gamma spectrometry, quantile classification. the cost of work. The integration of geophysical and other methods of remote sensing, performed using light unmanned systems, is an objective trend in the development of UAV-aerogeology, since the expansion of the set of available geodata significantly simplifies the interpretation of the geological situation and increases the reliability of decisions [5, 15, 16, 17]. Lightweight radiometric detecting modules with SiPM photodetectors do not affect the UAV flight time at all, even if two units are used to improve data quality, and not one, as in this experimental work. The spectrometers are heavier, but in many cases, when working on sites with an area of even tens of square kilometres, it is not necessary to use the maximal operational radius of the UAV; in such cases a spectrometer with a mass of 1 kg has little effect on survey performance. At the same time, a gamma survey is one of the most versatile and informative methods of geologic and geophysical mapping, and its application simplifies the interpretation of the data obtained. In this regard, over the past few years, a mono-method UAV-geophysical survey was seldom performed [15, 16], with the exception of geological situations when it is reliably known that the gamma survey at the site is not informative. The basic version of the SibGIS UAS assumes integrated magnetic and radiometric surveys during the first stage of geological prospecting of the sites (with a step between profiles of 100 m), and subsequent detailing (on a scale of 1:5000 and larger) with the spectrometric gamma survey. Figure 15 shows the UAS (a,b) and fragments of a spectrometric survey (d) carried out on such a detailing area in combination with a magnetic survey (c). The survey altitude is 35 m, 50 m between the profiles. In this case, some correlation between the anomalies of increased values of the uranium channel of the gamma-field and increased values or anomalies of the change in the sign of the magnetic field is noticeable. The source of the latter is fracture tectonics and zones of granitoid magmatism, and these are visible in both geophysical fields. Figure 16 shows fragments of a gamma-spectrometric survey at one of the sites in the Republic of Buryatia, the coordinates of which cannot be disclosed due to commercial sensitivity. It is interesting that the object of the contract was a UAV-magnetic survey, which is still in most demand in the geological prospecting market (results of the survey cannot be cited for the same sensitivity concerns), while the gamma survey was carried out by our own initiative. However, the results of gamma spectrometry turned out to be more informative than magnetic survey data. In the radioactivity field, the boundaries of sedimentary and igneous rocks are clearly traced, and according to the different ratios of uranium and thorium, there are also two formations of granites distributed over the area. Figure 16d shows another possible variant of UAV-gamma spectrometry--the variant of \"hovering\", which can be used to obtain high-precision concentrations of radionuclides with relatively large detectors [16], or as compensation for a very small volume of a gamma detector [6, 13].