###### Abstract  
Prior to restoration work, the frescoes created at the end of the XV century by the painter [PERSON] (1463-1518) in the apse of the Church of St. Panfilo in Villagrande di Tornimparte (L'Aquila) were the subject of a thorough diagnostic study involving several tests, from in situ non-destructive analysis to laboratory micro-destructive analysis on the collected samples. In this paper, we report the application of the sonic pulse velocity test, hygrometric tests, and infrared thermography to assess the state of conservation of the frescoes, i.e., the combined system of plaster and wall support. The complete analysis of the frescoes' state of conservation revealed significant insights. The integrity of the plaster was evaluated through sonic pulse velocity tests, which highlighted several areas of detachment or degradation phenomena. Hygrometric analysis described humidity variations, particularly near the boundary between the cach area and the church naves. Passive infrared thermography detected temperature inhomogeneities, emphasizing differences in the wall texture and the masonry structure. Moreover, by comparing sonic pulse velocity and passive thermography images, a certain degree of correlation between hot areas and slow areas in the presence of possible detachments was noticed. In addition, pulse-compression active thermography was applied in a few spots, and for the first time, to the best of our knowledge, the virtual wave concept was applied to the cultural heritage field. This strategy helps in better associating anomalies with depth. The measurement campaign was part of a research project conducted by members of the Italian Association of Archaeometry (AIAr), and the results were compared and integrated with those of other non-destructive and analytical methods. f 20  
The state of preservation of a fresco and the choice of the most suitable restoration procedure depends on the evaluation of many aspects, from the historical analysis of the artwork to the study of execution technique and materials used, and to the analysis of the support. The latter is generally a complex stratified system characterized by different constituent materials and construction techniques. Assessing the state of health and preservation of such structures is not straightforward, as many parameters are unknown--for example, the thickness and the number of the various layers, the materials used, etc. Among the NDT techniques, a few can penetrate the outer layers, the carbonated surface, and the painting layer, revealing info about the rough coat layer and the support, although possible detachments, the presence of water, and high humidity values can represent sources of structural damage and degradation phenomena that can affect the outer layers. Sonic pulse velocity (SPV) is a method that uses elastic compression waves generated by a mechanical impact on the surface of a sample to investigate the materials in depth [3; 4; 5; 6]. In the case of good adhesion between the painting layer and the underneath, and between the various layers in general, the elastic waves travel faster from the source point to the receiver points. Conversely, detachments, voids, and discontinuities of the plaster can hamper the propagation of the elastic waves, resulting in a lower sound propagation velocity. In addition, by integrating the results of SPV tests with those obtained from other techniques, detachments, microfractures or lesions, and inhomogeneous areas can be distinguished [7; 8]. A high level of humidity or the presence of water are two other aspects that can influence the measured velocity. While on the one hand, the presence of water affects the sonic velocity, causing a general increase [9], on the other hand, this is the main cause of the degradation of frescoes, leading to a general decrease of velocity [10]. To distinguish between a low velocity due to moisture/water or by detachments/weak adhesion, complementary information must be acquired.