Swedish-Italian joint project on: "House of Augustus: non invasive multispectral imaging of interior walls for sustainable preservation and risk assessment"

Early diagnostics and documentation fulfil an essential role for an effective planning of conservation and restoration of cultural heritage assets. We present here part of the results of a joint Italian-Swedish project focussed on the assessment of the conservation status of the Casa di Augusto, an important Roman archaeological site. The site, that is only partially open to the public, is located in the south-west area of the Palatino hill in Rome, Italy, and was the private residence of the Emperor Augustus. The project was focussed on documenting and recording the status of some sections of the part closed to the public by using different non-invasive imaging techniques, from high-precision colour 3D Laser Scanner to fluorescence hyperspectral imaging lidar. The lidar used a tripled-frequency Nd:YAG laser emitting at 355 nm as excitation source and an intensified, gated 512x512-pixel CCD as detector. The lidar had imaging capabilities thanks to a computer-controlled scanning mirror. The studies included both the characterisation of historic materials and the detection and characterisation of biodeterioration processes occurring on the site walls. The diagnostic techniques were completely non-invasive. The first stage of the project focussed on a spectroscopic study of several fragments, mainly made with the fresco technique, coming directly from the site. The samples were measured by means of a hyperspectral fluorescence lidar to investigate the potential for their characterisation on the basis of their fluorescence properties with a remote sensing technique. The samples were also characterised using several spectroscopic techniques: micro-FTIR and FT-Raman spectroscopy for the identification of the pigments; ATR FTIR for the identification of binders and substrate. The second stage of the project focussed on remote sensing measurements at the site. Measurements were performed both with the 3D laser scanner and with the imaging fluorescence lidar. Portions of selected walls of the monument were measured by the lidar system to obtain a laser induced hyperspectral fluorescence image achieving a spatial resolution of the order of 1 cm. Selected walls comprehended both frescoed and non-frescoed surfaces. Frescoed surfaces were measured both to obtain a detailed map of the pigments and for the detection of the presence of phototrophic biodeteriogens. Non-frescoed surfaces were mainly analysed to better characterise the microbial communities present on the surface. Biological sampling, followed by cultivation in the laboratory and identification by molecular methods completed the information collected at the site.