Suitability of hyperspectral imaging technique to evaluate the effectiveness of the cleaning of a crustose lichen developed on granite

Abstract The aim of this paper was to evaluate the effectiveness of the laser cleaning of a complex biogenic patina, a crustose lichen, by means of hyperspectral imaging techniques. Samples of a Hercynian granite from NW Spain colonised by an endolithic crustose lichen (Pertusaria amara) were collected and cleaned following three procedures: a scalpel, the third harmonic of a Nd:YVO4 ns laser and the scalpel followed by the laser. The suitability of the hyperspectral camera as a non-destructive, online, fast and in situ monitoring technique to assess the effectiveness of the cleaning was evaluated using optical microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and colour measurements in CIELAB space. The hyperspectral imaging technique allowed us to measure the reflectivity variations of the cleaned surfaces in a non-invasive way, allowing the identification of the cleaning effectiveness of each procedure. Nevertheless, the results of the hyperspectral imaging technique must be validated by conventional techniques.

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