## 2 Research Aims, Materials, and Method
### Methodology
#### 2.2.2 Literature Assessment
To put together the database to analyze, the decision was made to run a semi-automatic document search guided by the operator's background knowledge. In practice, two main routes were followed. On one hand, documents falling into the above categories were searched directly by browsing the institutional websites and publication repositories of the
public heritage bodies of the European countries. The rationale was to search for evidence of the use of RS and EO by heritage institutions \"directly from the source\". The search was not restricted to only central administrations but also encompassed regional to local administrations. Furthermore, to provide the most comprehensive picture, we considered texts published in different languages (English, Italian, Polish, German, etc. ), for example, for Spain, Ministerio de Cultura y Deporte--Gobierno de Espana and Instituto Andaluz del Patrimonio Historico; for Italy, the Italian Ministry of Culture and the Archaeological Park of Colosseum; and for Germany, the State Office for Cultural Heritage Management Baden-Wurttemberg. This choice was made under the assumption that, depending on the specific governance and administrative hierarchy and associated roles and mission (that may vary from country to country), policy, guidance, and technical documents may be issued at different levels. Therefore, the search aimed to be as inclusive as possible. On the other hand, an automatic search using keywords (the same combinations as per the indexed literature) was run through a Google search engine. This route mainly enabled the collection of a body of technical reports and non-indexed conference proceedings. For the period 2008-2022, the total number of documents retrieved was 77. As expected, these documents were found to be very heterogeneous in typology and content, and the technical terminology therein was quite diverse, even the terminology used to mean the same type of RS or EO technology, damage, or threat. Decimation. Therefore, there was a need to run two tasks, i.e., tagging and indexing of the text and, afterward, \"skim-reading\" and manual checks. In practice, the text of each document was screened to tag the technical terms (see also Appendix B) specifically related to \"Type of heritage\", \"Technology\", and \"Threats/factors/hazard\". Each tagged term was recorded in its original form, alongside the number of its occurrences in the various sections of the document. The latter quantitative information was already indicative of the relevance to the scope of the present assessment. As mentioned in Section 2.2, isolated textual occurrences without any clear evidence of dedicated narration or discussion were disregarded during the skim-reading task. This task required an in-depth reading of the documents to contextualize the tagged terms and indexed text. At the end of this process, 19 documents were kept to input into the statistics evaluation. Definition. Finally, to solve the terminology heterogeneity and make the Grey literature comparable with the indexed literature, the tagged terms were converted to match and fall within the terminology for RS technologies adopted in the present study (Figure 2) and UNESCO categories of factors affecting properties [24]. This step was also helpful in addressing the redundancy in the terms used within the same document. Although different terms are descriptive of different types of heritage or technology or threats and thus express the variety of real-world conservation situations and the specifics of the employed technologies, for the purposes of this study, their conversion to the main common categories makes the assessment more effective without compromising the key information. Appendix A reports an example of terms' conversions and categorization to explain the process.