## 5 Conclusions  
In this review of the current scientific and Grey literature focusing specifically on monitoring hazards to cultural heritage across Europe through remote sensing and Earth Observation technologies, we tried to answer a few fundamental questions: (i) What are the types of hazards to cultural heritage that have been studied using satellite imagery so far? Are all types of hazards equally addressed? and (ii) Is there a correlation between a specific type of damage and satellite-based technology? While we acknowledge that the issues affecting this field of application are broader than those sampled by these research questions, they have not been previously investigated in the literature, and the results presented in this paper highlight findings and observations that could not necessarily be predicted. Thus, the results corroborate the working hypothesis and the fact that it was appropriate to start investigating these subjects. From the results presented, we can conclude that the most studied types of hazards do not truly reflect the hazards that represent the major threats to the monuments that have been monitored, with a significant unbalance towards \"Sudden ecological and geologic threats\", \"Management\", and \"Other human activities\" (e.g., looting or war). Hence, one recommendation coming from this research would be that, together with the heritage stakeholders, the scientific community should consider a more balanced focus on damage categories and/or hazard factors that have been considered. The present gap may be due to the limited understanding and use of satellite images by multiple end users to tackle different types of factors such as agriculture and urban sprawl. This assumption fits well with previous research studies on this and other related topics [4; 12; 13]. The construction of multidisciplinary collaborations, including satellite image specialists and non-specialists from different application fields, may certainly help to fill this gap and test the full potential of satellite technologies for documenting and monitoring endangered heritage. This can be implemented through capacity building and training sessions, as demonstrated by recent examples [13; 14; 15; 16; 17; 18; 19; 20]. Another issue regards the terminology. The literature is currently characterized by a wide variety of terms, even to indicate the same or similar threats. Using common terms facilitates comparisons and research replication. As demonstrated in this study, a significant effort has been made to normalize terminologies regarding threats to cultural heritage. One possible solution could be that of relying upon the UNESCO terminology (2010) used in this paper, which nowadays represents the most comprehensive attempt to map the whole repertoire of factors affecting cultural properties worldwide. The separate analyses of both scientific and Grey literature highlight that there is no direct correlation between the types of hazards and the potential RS technology used to monitor them. On the other hand, the analysis of both batches of the literature reveals how the geospatial environment is the most suitable framework for data integration for both RS experts and non-expert users. Also, aerial photography (increasingly through UAV devices) is another common ground for both scientific and Grey literature. These results suggest that users sampled in the Grey literature are familiar with managing photography, orthophotos, and satellite imagery for consistent visual interpretation. However, although acknowledged, the full benefits of satellite data processing and especially in combination with specific technical solutions such as ground sensors, still remain unlocked for the larger public. Looking closer into the numbers, the analysis of this study shows how there are apparent successes of the Copernicus programme and Sentinel imagery (predominantly Sentinel-1 and -2). With their FOF access policy, the Sentinels have had a significant impact on the studies regarding the cultural heritage sector in the past ten years.