Appraisal of Opportunities and Perspectives for the Systematic Condition Assessment of Heritage Sites with Copernicus Sentinel-2 High-Resolution Multispectral Imagery  
[PERSON]  
1 Italian Space Agency (ASI), Via del Politecnico snc, 00133 Rome, Italy; [EMAIL_ADDRESS]  
2  
[PERSON]  
2  
Italian Space Agency (ASI), Via del Politecnico snc, 00133 Rome, Italy; [EMAIL_ADDRESS]  
2  
Footnote 2: email: {e.g., {e.g. interpreting features, as well as a priori knowledge and expectations on what to see, are all factors influencing the level of accuracy that can be achieved in the satellite-based assessment. In the last years, optical remote sensing has proved extremely valuable in reducing the uncertainty about the condition of heritage assets across the Middle East and North Africa (MENA) region and, more generally, in the Mediterranean countries. Several initiatives at both the international and national level are ongoing. For example, the UNESCO Emergency Safeguarding of the Syrian Cultural Heritage project [2], the American School of Oriental Research Cultural Heritage Initiative (ASOR CHI) [3], the Association for the Protection of Syrian Archaeology (APSA2011) [4], and the Endangered Archaeology in the Middle East & North Africa (EAMENA) [5]. These projects collect information from satellite imagery not only to map the extent of damage and destruction incurred by built and movable heritage during crises, but also to assess the impact of modern human activities in ordinary times, such as agricultural exploitation of land, urban expansion, and infrastructure construction. As recently recalled by [PERSON] and [PERSON] [6], the above-mentioned projects demonstrate that the research and user communities are moving from site-based studies and single-incident substantiations to more systematic, regional-scale efforts over larger regions. However, such large spatial coverage and monitoring of a multitude of sites at the same time still pose operational challenges; first of all, the need to access large volumes of timely and updated satellite imagery at a suitable resolution. Satellite data uploaded onto open visualization platforms (for example, Google Earth and Bing maps) have partly contributed to solving this issue and are now Earth observation facilities incorporated into the image interpretation methodologies of some of these heritage initiatives (for example, Reference [5]). The optical images used for such studies mostly come from satellites operated by commercial companies (for example, WorldView and GeoEye) because of their sub-meter spatial resolution. For instance, the potential for looting detection has been recently discussed in Reference [7]. To avoid confusion on terminology, in this work, we adopt the classification by which optical satellite imagery is referred to as'very high resolution' (VHR) if characterised by a spatial resolution of 5 m to even less than 1 m, and 'high resolution' (HR) if the spatial resolution is between 5 and 30 m; see, for example References [8; 9]). From the point of view of research development, the emphasis on the exploitation of VHR images--mostly driven by the need for searching for very small features--has led to very few publications that specifically investigate the role that regularly acquired HR images from constellations such as the Landsat missions may play in this application domain. It is also to be noted that most of these publications rather concentrate on land use impacts in the surroundings of the sites and/or their buffer zones and conservation areas. These often exploit broad classification schemes for their assessment (for example, urban versus agricultural [10; 11]), but seldom focus on the recognition of specific man-made features and tracking of the temporal evolution of their patterns. On the other side, the Sentinel-2 multispectral constellation of the European Commission programme Copernicus [12; 13; 14] is an Earth observation system that is increasingly gathering attention in archaeological remote sensing.