Long-range remote spectroscopy for wall paintings and architectural interiors (Conference Presentation)

Material analysis is important to the study of architectural interiors and wall paintings in order to inform the research in history and to monitor the state of conservation. Multimodal spectral analysis is increasingly used in mobile lab campaigns conducted in situ at historical sites. Some challenges specific to the investigation of immovable cultural heritage arise from the inaccessible heights and remoteness of the sites. Therefore, complementary spectroscopic techniques that can be conducted from the ground at a large distance (> 3 m) are required. The Imaging and Sensing for Archaeology, Art history and Conservation (ISAAC) Mobile Lab routinely employs remote spectral imaging to record the spectral reflectance in the visible and near infrared of wall paintings at high spatial resolution per pixel. Raman spectroscopy identifies molecular structural fingerprints by observing the spectral shift from the excitation laser wavelength resulting from molecular vibrations. A by-product of Raman spectroscopy is laser induced fluorescence spectroscopy (LIF). Laser-induced breakdown spectroscopy (LIBS) detects characteristic lines for different elements from the plasma created by high power laser pulses. The combination of Raman, LIF, LIBS and spectral reflectance can provide complementary material information about the artworks: molecular structure and elemental composition. Assisted with a computer-controlled telescope mount, small area remote spectroscopic mapping (2D scanning) with Raman and LIF is also achieved to complement long range remote visible and near infrared spectral imaging. In this work, we present the developments of a combined long range mobile remote spectroscopy system for working in the range from 3m to 15m, and its recent applications in remote material identifications on wall paintings.