Can we unlock more information from interferometric sensors? Feasibility and performance analysis

The surface is the most representative part of an artwork and it is also the part most exposed to alterations due to interaction with the surrounding environment. Non-destructive surface monitoring is of crucial importance in preserving and conserving cultural heritage and optical interferometric techniques allow to acquire the surface structure down to the submicrometric scale. In this work, we start from laser microprofilometry based on conoscopic holography sensors to unlock a new way of measuring the surface. In the last years, this technique has proven effective for surface diagnostic in heritage science providing high-quality surface dataset on diffusive, highly reflective, and polychrome artworks. However, an open problem in profilometry is the spatial referencing of surface topography at the micrometer scale, due to the lack of references in the height data with respect to the visually readable surface. We have recently developed a solution that exploits the raw intensity signal collected by the single-point sensor (i.e. the backscattered signal of the laser diode) and the interferometric height dataset, which are intrinsically registered. This method provides additional information about material texture, color variations or artist's marks that enable spatial registration and data fusion tasks, otherwise difficult in traditional laser profilometry. In this paper we analyzed the feasibility and the performance of the whole process chain from the acquisition to the exploitation of the dual height-intensity datasets, focusing the attention on the raw intensity signal interpreted as a "raw reflectance signal". We demonstrate the effectiveness of the proposed approach by presenting results on exemplary case studies.