Fiber optics reflectance spectroscopy (FORS) and visible and near-infrared (VNIR) hyperspectral imaging (HSI) were applied to assess and control the laser cleaning process of a deeply darkened limestone surface collected from the historic entrance gate of Castello Svevo, Bari, Italy. Both techniques enabled us to verify the different degree of removal of a thick deposit of black crust from the surface of the walls. Results obtained were in good agreement with those of previous studies of the elemental composition achieved by application of laser-induced breakdown spectroscopy (LIBS). Coupling FORS and VNIR-HSI provided important information on the optimal conditions to evaluate the conservation status and determine the more appropriate level of cleaning restoration, thus avoiding over- and/or under-cleaning. Imaging spectroscopy was used to obtain maps of areas featuring the same or different spectral characteristics, so to achieve a sufficient removal of unwanted layers, without modifying the surface underneath, and to increase the efficiency of traditional cleaning techniques. The performance of the combined non-invasive approach used in this work shows promise for further applications to other types of rocks and highlights the potential for in situ assessment of the laser cleaning process based on reflectance spectroscopy.

中文翻译：

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通过光纤反射光谱（FORS）和可见光和近红外（VNIR）高光谱成像（HSI）评估石灰石纪念碑的激光清洁

应用了光纤反射光谱（FORS）和可见光和近红外（VNIR）高光谱成像（HSI）来评估和控制从意大利巴里Castello Svevo历史悠久的进口处收集的深黑色石灰石表面的激光清洁过程。两种技术都使我们能够验证从墙壁表面清除黑皮厚沉积物的不同程度。获得的结果与先前通过应用激光诱导击穿光谱法（LIBS）获得的元素组成的研究结果相吻合。FORS和VNIR-HSI的耦合提供了有关最佳条件的重要信息，以评估保护状况并确定更合适的清洁修复水平，从而避免过度清洁和/或清洁不足。成像光谱法用于获得具有相同或不同光谱特征的区域图，以便在不改变下面表面的情况下，充分去除不需要的层，并提高传统清洁技术的效率。这项工作中使用的组合式非侵入性方法的性能显示出有望将其进一步应用于其他类型的岩石，并强调了基于反射光谱法对激光清洗过程进行原位评估的潜力。