Non-Invasive Monitoring of Architectural Heritage

Abstract: The on-site documentation and examination of architectural heritage has presented challenges for traditional analysis methods in the form of, among other things, large complex structures, sites and environmental conditions. In recent years there has been growing interest in assessing progressing deterioration processes and material analysis, with an emphasis on sustainable conservation and maintenance planning. Today, new non-invasive examination and visualisation methods are becoming increasingly important in the study of cultural heritage. Furthermore, increased awareness of complex on-site conditions and of the impact of climate on the built heritage has led to advances in monitoring and prediction technology in order to aid on-site studies, with a focus on mobile techniques. Within this context, new remote sensing techniques are also being developed, in addition to various laser-based techniques as analytical tools, such as laser-induced fluorescence. In order to address the challenge of complex analysis situations in an outdoor environment, the present research aimed to investigate the potential of a remote sensing method involving the use of two mobile systems. The study focused on the architectural surface of historical monuments, mainly on stone and brick materials, using a laser-induced fluorescence technique to monitor a building from a remote location. The study is in the form of a multiple case study research project using a mixed methodology strategy to provide context and sufficient data for the analysis of building status and aspects of deterioration, both for traditional building documentation and the fluorescence analysis. There were cases studies: Övedskloster in Sweden, the Coliseum Amphitheatre and the Lateran Baptistery in Rome. These produced information on conducting remote investigation on site and the possibility of conducting interdisciplinary studies as well as providing support for supplementary laboratory studies. The use of a non-invasive technique indicated a potential for remote analysis, with the ability to scan the façade from up to 65 metres, and early detection of non-visual phenomena by means of fluorescence. In addition, it was possible to visualise monitoring phenomena on historic façades by means of thematic mapping and, where hyperspectral imaging could suffice, visualisation of analysis. The research demonstrated the early detection of biodeteriogens in fluorescence on areas that were difficult to assess from ground level, for identification as well as for an initial assessment of the chlorophyll content, which could indicate a need for further monitoring as well as pointing out areas requiring further analysis of species categories and potential spread. The initial characterisation of surface material, both previously known and non-visual, was also investigated. This could prove useful when planning conservation decisions and sustainable maintenance. The technique could also serve as a basis for the identification and initial assessment of the contribution of chemical treatments, soiling and biodeteriogens, where monitoring of large architectural structures is required. Finally, the technique may be particularly suitable for providing an initial indication for planning maintenance and/or for the future minimum conservation of large-scale objects, especially in the outdoor environment where uncontrolled external conditions are inevitable. This could also help with suitable documentation over time by monitoring changes and the speed of the deterioration processes by means of repeated whisk-broom scanning at regular intervals over time. It could also be used as a tool in conservation maintenance planning.

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