Hyperspectral instruments as potential tools for monitoring decay processes of historical building surfaces

The effects caused by weathering on historic buildings and outdoor artefacts impose new strategies for their sustainable preservation. The large scale monitoring of the decay evolution of exposed surfaces, using non- destructive and relatively low cost techniques, is the first condition to: (a) contribute to construct semi-empirical alteration models of artefacts; (b) plan suitable conservation strategies and assess their efficacy. Among non-destructive technologies for “in situ” analysis, hyperspectral instruments, like portable spectroradi- ometers (PS) and imaging spectrometers (IS), provide information on the characteristics of different materials, as well as the identification and discrimination of different compounds on the basis of their patterns of absorp- tion at specific wavelengths (Clark et al.,1993). The spectral range usually covered by commercial and prototypal hyperspectral sensors is generally comprised between 400 and 2500 nm. Hyperspectral analyses may be used to: • detect degradation products, i.e. gypsum, on surfaces of stone artefacts and monumental buildings; monitor the presence of restoration/conservation treatments; produce compositional maps of specific phases/compounds; provide information on the characteristics and properties of crystal phases, such as their grain size. Our research group has started a project aimed at verifying the suitability of hyperspectral analyses applied to the field of Cultural Heritage (Vettori et al., 2008; Camaiti et al.2011).