# UAV-Based Evaluation of Rockfall Hazard in the Cultural Heritage Area of Kipinas Monastery, Greece
## 5 Discussion  
In this study, a new Rockfall Hazard and Risk Rating System has been proposed and the implementation of a methodology has been suggested in order for all the critical parameters of the system to be estimated. Through this, a semi-quantitative rockfall hazard and risk assessment was performed. As presented above, many rating systems for rockfall assessment have been proposed during the past decades, but nowadays, with the rise of remote sensing technologies in the field of geohazards, it is believed that there is still margin for improvement. Therefore, the construction of a new rating system based in quantitative parameters, exported from the UAV-derived data, was considered as an appropriate evolution in rockfall hazard and risk assessments. The qualitative-based approach (i.e., rating system) was selected over a quantitative one, in order to cover a wider range of applications in areas susceptible to rockfall events with negligible to nonexistent data from former rockfall-related events. The main target of the proposed methodology is not to replace the detailed quantitative analyses of rockfall events, but to be considered as the initial step towards rockfall hazard and risk assessments with the implementation of it to the investigated site as a whole in order to classify it to sub-regions regarding their hazard and/or risk level, respectively. Through its application, useful information for hazard and risk management will be provided, for relative comparisons of different sites and also for facilitating the prioritization of mitigation measures. Then, of course, if it is deemed necessary, a detailed quantitative character, with thorough ratings to numerically differentiate the hazard and/or risk, respectively, could be adopted at the already predetermined susceptible regions of the site [75]. The main point that sets the current approach apart from its predecessors is the type of the value of the implemented factors. Generally, rating systems constitute a qualitative type of assessment, but this does not mean that the value of the factors that comprise them have to be qualitative-based. The main disadvantage of qualitative-based values is that they are subjective. This means that in the same area, with the same available data, the results could vary significantly between different researchers. On the contrary, the value of the factors of this proposed rating system are quantitative-based. The UAV-derived data, in accordance with the appropriate computer-based processing, enabled the calculation of important parameters in order for the properties of the complicated phenomena of rockfalls to be understood and expressed in absolute values. Factors regarding the Total Kinetic Energy, the rock block distribution across the slopes (fallen and potentially unstable) and the mode rock block volumes (fallen and potentially unstable) that are absent in most of the prior well-established rating systems such as RHRS [82] and its modifications [24; 84; 85; 86; 87; 88; 89; 90], RHI [11] and the rockfall risk rating systems proposed by [105], comprise the cornerstone of this newly proposed Rockfall Hazard and Risk Rating System. The methodology that was followed in this particular study and the parameters that were decided to form the rating system may seem to be related to a quantitative-based analysis at first glance. Specifically, the detection of potentially unstable rock blocks, the estimation of their potential volumes and the probabilistic analysis of them based on trajectory simulations are very common approaches that are followed in quantitative analysis, in sites with extensive rockfall-related multi-temporal inventories [106; 107; 108]. In such cases, a multi-temporal change detection procedure between the different datasets is performed, in order for topographical changes between different epochs to be monitored and characterized for modeling of the rockfall's dynamics. Consequently, the aforementioned values can be estimated.