Mobile terahertz spectroscopy for in-situ evaluation of structural characteristics in wooden artefacts

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Abstract Conserving fragile wooden artworks requires diagnostics that detect minimal structural changes without invasive intervention. We used a robotic-arm terahertz time-domain spectroscopy (THz TDS) system to study the centrepiece of the Marienaltar in Isenhagen Monastery (Hankensbüttel, Germany), a polychrome, gilded winged altarpiece from the early 16th century. Analyses revealed severe limewood deterioration from insect damage (notably Anobium punctatum ) and fungal activity linked to fluctuating climate; prior restorations were identified via archives, visual inspection, and material analysis. Due to the object’s fragility, restoration was performed in situ. Robotic THz TDS enabled non-contact measurements before and after treatment, assessing sensitivity to subtle structural changes from consolidation. Results show THz TDS detects millimetre-scale changes beneath the polychromy, providing objective evidence of treatment effectiveness. This case demonstrates the potential of robotic THz TDS for long-term monitoring and quantifying restoration impact, advancing evidence-based conservation.