## 3 Results
### Results of the Literature Assessment
#### 3.1.3 Grey Literature
Proximity and terrestrial RS measurements are indeed quite spread in the Grey literature, with \"Ground sensors\" accounting for 12%, \"Photogrammetry\" accounting for 7%, and \"Terrestrial laser scanning\" accounting for 5%. These percentages would therefore contrast with those found at the sub-category level. The hypothesis is that this outcome could be an effect of the diversity in specific terminology used in the analyzed texts. So, in reality, the representation would be much higher than the above statistics would show. Indeed, the careful reading of the indexed texts highlights that overall, despite the specific terminology used, a wide variety of technologies are currently known and employed in heritage practice. Regarding \"Satellite Remote Sensing\" ranking third among the macro-categories (17%, Figure 12), it is worth noting that it ranks second when technology sub-categories are accounted for (12%, Figure 13). In particular, the latter percentage refers to the use of \"Optic and/or multi-spectral\" satellite images, which predominates in the use of \"Radar and/or InSAR\" data (7%, Figure 13). This outcome aligns with similar observations reported in previous reviews [4] and confirms the general consensus that archaeologists, heritage scientists, practitioners, and heritage officers are much more acquainted with data collected in the optical portion of the spectrum. Insights into whether these statistics correspond to the actual use of satellite data in daily practice are provided in the discussion (see Section 4). In the Grey literature, RS and geomatic technologies are described in relation to a broad spectrum of threats and factors affecting the properties that in the present research are analyzed as per the definition complying with UNESCO's lexicon. Figure 14 shows the distribution of threats and factors, from which it is clear that in the Grey literature, there is no predominant factor or group of factors significantly distancing the others. This is a substantial difference from the situation observed in the scientific literature (cf. Figure 3b). In particular, the statistics suggest that the first sources of concern include human actions, impacts due to modern development, agriculture, and the use of natural resources. These are followed by climate and severe weather events and their cascading processes such as flooding, desertification, and changes in weather parameters (e.g., temperature, pH) and factors related to maintenance and management of sites. Some caution should be paid to the interpretation of the lower ranking of \"Local conditions affecting physical fabric\" (6%)--which include erosion, weathering, rain, rising water tables, and micro-organisms. These threat factors, whi  
Figure 14: Distribution of Grey literature according to hazards and damage factors as defined according to UNESCO’s lexicon [24]. For the sake of visualization the “Others” category aggregates factors that account for less than 5% each. Please note that all percentages are intentionally rounded to the unit, without decimals. The total sum is 100%. ordinary maintenance and conservation, are mostly addressed by heritage bodies and organizations by means of other types of technologies than those of interest in the present research and, for sure, than the top-ranked macro-categories (see Figure 12). A temporal analysis of the Grey literature highlights that the threats that appear to be the first sources of concern (see above), as well as climate and severe weather events, are consistently present through time (Figure 15). No specific trend is observed. These statistics show that the analyzed documents mostly cover more than one factor. The key evidence, then, is the confirmation of the plurality of threats that heritage bodies and organizations need to account for and mitigate. Therefore, diverse factors are addressed by different RS and geometric techniques, depending on their technical specifics and proven capabilities.