Ambient light VNIR hyperspectral imaging for pigment analysis in Martu rock art

Abstract Pigments in open-air rock art are often in heavily deteriorated superimposition sequences, limiting visualisation using standard photographic approaches. Hyperspectral imaging (HSI) is emerging as a portable, non-invasive approach for in situ pigment analysis, but collection of spectral-spatial information typically relies on controlled illumination, which is challenging in remote settings. This study evaluates the performance of visible-near infrared (VNIR) HSI for pigment analysis in rock art under variable ambient illumination. HSI data were collected from a Martu rock art panel featuring faint red and white pigments over one day, and the effects of illumination variability and surface variegation were assessed through comparison with 3D modelling. Reflectance spectra provided broad mineralogical insights, while spectral decomposition consistently delineated pigment-related information across a range of illumination conditions. The findings support ambient light VNIR HSI as a practical, non-invasive method for pictographic rock art analysis, with recommendations for best practice data acquisition and analysis.