Thermographic Data Inversion Procedures. Architectural and Environmental Applications

The research activity was focused on development, testing and application of numerical methods for solving the thermal problem and analyzing thermographic data in the architectural and environmental fields. First, numerical codes, based on the Conservative Finite Difference approximation, were implemented in MATLAB environment to solve the 1D and 2D heat conduction problem. The codes allow to simulate the thermal response of homogeneous and in-homogeneous media by varying both geometry (i.e, width, depth) and thermal properties (i.e., thermal conductivity, specific heat, density) of the constituent materials and initial internal temperature distribution. The numerical analysis has provided, with a good level of accuracy, joint information about both nature and geometry of anomaly sources of homogeneous or multi-layer structures, even if IRT data come from short times of heating and cooling phases, which do not allow for reaching of the thermal equilibrium. The codes have been also applied to IRT data for architectural and environmental studies. As concern the application to architectural structures, IRT data acquired on two different archaeological buildings were analyzed. The first quantitative analysis refers to data acquired in the Marcus Fabius Rufus’ House, located in the archaeological area of Pompeii (Naples, Italy). The numerical study has permitted to discriminate layered structures and to identify the state of conservation of the constituent materials. The second application in architectural field regards a quantitative analysis of IRT data acquired on the east wing of the Dome of Magdeburg (Magdeburg, Germany). The numerical study allowed to characterize the plaster score made of three layers, i.e. a lime wash layer that overlaps two lime mortar layers. In particular, depth, thickness and nature of the thermal anomaly sources were defined and attributed mainly to degradation of the lime mortar layer at different depths. Such results have provided helpful indications for restoration work planning. As concern the applications to environmental field, a numerical analysis was performed in the attempt to reproduce the thermal evolution of the Phlegraean magmatic system (Naples, Italy) during the last 40,000 years. A careful study on the initial values of the physical properties of the Phlegraean caldera geological structure was conducted. The main finding is that temperatures measured in the geothermal wells drilled inside the caldera at depths larger than 2,500 m can be reproduced under the assumption of conduction heat propagation, while hydrothermal convection has to be taken into account to properly describe heat propagation above such depths. Furthermore, a new method for analyzing long-term time series of IRT data recorded by a permanent network located at the monitoring station of Pisciarelli (Campi Flegrei) was developed. The proposed approach is based on the evaluation of temperature changes of the investigated area during the last seven years. So far, downward trends at the end of 2007 and during the entire year 2012 are identified, and possible correlations with the results from different analyses and GPS elevation data are work in progress. Finally, a new approach to invert IRT data based on the Prony’s method has been proposed. The application of the method to synthetic and experimental thermal data showed significant correlations between the exponential coefficients coming from the Prony’s analysis and the physical properties of test homogeneous materials. The interpretation of the inverted results is more difficult when inhomogeneous structures are considered and the search for possible correlations is currently in progress.