PSI - Issue 64

Luigi Petti et al. / Procedia Structural Integrity 64 (2024) 629–636 Petti L., Zuchtriegel G., Lupo C., Calvanese V. & De Gaetano C.M. / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 4. Example of AIX (a) and RDI (b) assessment in the case of Insula 4 Regio I.

5. General Assessment Level (GA) The General Assessment Level consists of a broad survey that provides a sufficient knowledge of the overall condition of the site. It is carried out by expert operators by means of drones and, when necessary, artificial intelligence (AI) applications. This level aims to constantly monitor possible at-risk areas, or criticalities, that could affect the archaeological heritage and to quickly manage eventual emergency conditions, like rain and windstorms, landslides, fire, etc. In general, GA is carried out monthly and consists of a drone survey of the site, where a high resolution image is obtained and analysed with the aim of assessing possible criticalities. The assessment consists of checking eventual evolutions through time-lapse surveys. The drone survey covers an area of 3.6 km² and is performed from a height of around 90 m. The drone can be controlled remotely via a cloud and has a wingspan of 1.2 m, a dual-communication system (including a Wi-Fi radio link and mobile connectivity via 3G network), an integrated GNSS, and it is possible to preset the flight path. The camera is an RGB type with an image resolution of 21.4 Mpx. The experimentation uses two types of drone image, one is composed of two images, where each one represents half of the ancient city, and the other one is an overall image. Both types are compared with each other. In this case study, approximately 180 points have been used for the image of half the city, and over 350 points for the overall image of the site. Figure 5 shows the overlay of a sample orthophoto and its corresponding GIS data. The orthophotos allow for both the identification of possible criticalities within the site and general evolution across the site. To this end, the georeferenced images are analysed with a semi-automatic procedure, which consists of identifying and reporting an intensity value (low, medium, high) for the most significantly changed elements. Five types of criticalities have been so far identified: water accumulation (WA), damaged sheaths (DS), presence of vegetation (PV), falling elements (FE) and disconnected elements (DE). The assessed potential high-risk areas are reported in a table, which allows for the information to be treated in a more streamlined way. The following information is inserted into the table: • Date_flight – refers to the date of last drone survey, against which criticalities are assessed. • Date_reference - the date of the reference flight, against which the evolution is assessed. If the reference date matches the flight date, the file describes all potential criticalities at the time of flight. If the dates are different, the file reports only the new criticalities or the ones for which the intensity has increased. • Criticality - description of the type of the criticality. • Criticality_Code - code associated with the type of criticality. • Number - Serial number of criticality for each type. • Intensity - express the intensity of criticality: 1 = Low; 2 = Medium; 3 = High; 0 = No longer detected; • REF_TOP - topographic reference of the areas where the potential criticality is detected, according to the Park’s description. The rooms not classified in GIS (without topographic reference) are highlighted in yellow on the table. • X_coord and Y_coord - geographical coordinates consistent with GIS representation.