_applied sciences_  
Editorial  
Infrared Imaging and NDT  
[PERSON] \({}^{1,*}\)+\({}^{\copyright}\) and [PERSON] \({}^{2}\)\({}^{\copyright}\)  
This challenging problem is very difficult to solve using an analytical method. In this case, the authors propose a different strategy: using a simple multilayer problem where only one resistive layer is estimated. In addition, they propose an asymptotic development method to simplify inverse processing. The paper addresses the inability of some methods, such as thermal signal reconstruction, to provide quantitative results by incorporating a calibration process base on the complete analytical quadrupole solution. The paper describes the experiments, camera configuration, and heating. The proposed procedure presents major advances, such as the possibility to address any type of multilayer material or fast inverse processing. Results indicate that the thermal resistance field can be calculated with an accuracy lower than 5% in less than 5 s.  
In [4], Dr. [PERSON] et al. present an application of active thermography to the analysis of multilayer wooden cultural heritage objects. In this case, pulse-compression thermography is applied to the sample to avoid damaging the fragile object during heating. Using this technique, a very low thermal contrast is enough to highlight the defects when using the proposed image processing method. This work proposes using the Hilbert transform to increase defect detection and characterization, and a novel normalization technique based on absorbance estimated by considering a characteristic value of the compression peak. The inspection method is applied to an inlay sample created by a professional restorer. Two experiments are performed using different cameras: an uncooled camera and a middle-wave camera. Results demonstrate the success of the proposed approach, providing high SNR and defect detection capability. This approach makes the inspection of very fragile art pieces possible, which otherwise would be damaged during heating when using active thermography. Another application of active infrared thermography to cultural heritage is presented in [5]. This work evaluates the capability of infrared thermography to differentiate between different types of historical glass. This approach can be used, for example, to distinguish previous restoration interventions. The experimental procedure is based on halogen lamps heating the samples. Measurements are performed in reflection and transmission mode. The sequence of infrared frames acquired is processed, first by calculating an average and then by subtracting this average from each frame. The resulting sequence is then analyzed using two clustering algorithms: K-means and hierarchical clustering. Results indicate the proposed inspection method differentiates between different groups of glass panes, with clustering providing more reliable results. In addition, it provides faster results while reducing time-consuming manual analysis. The conclusion is that active infrared thermography shows potential for documenting the material intervention history of leaded-glass windows during or in preparation for conservation treatments. A study about the characterization of the lateral dimension, depth, and inclination of buried tilted rectangular heat sources is presented in [6]. The novelty of this work lies in the consideration of an arbitrary inclination of the heat source with respect to the surface of the material, a problem few works have addressed. To analyze the problem, the authors present a semianalytical expression for the surface temperature distribution produced by a rectangular heat source of any inclination. A model is fit considering two perpendicular temperature profiles and the temperature history at one position. Moreover, the optimum experimental conditions are analyzed. Synthetic data with added noise and experimental data taken with an inductive thermography setup are used for testing.