Working Process Development For Weathering Degree Mapping Of Stone Monument Using Reflectance Spectroscopy

Most stone monuments have been weathered on the field with exposure of rain and wind during hundreds or thousands years. Reflectance spectroscopy can be applied to assess weathering degree of those stone monuments composed of granite which is the most general material of stone monument in Korea. Weathering degree was analyzed by using reflected and transmitted electromagnetic energy based on the theory of reflectance spectroscopy on the surface of rock to identify rock forming minerals using their diagnostic spectral absorption features. This method could be used as an improved nondestructive assessment method compared with conventional subjective and qualitative assessment methods. We tested feasibility of this technique for actual granite stone monuments. Granite is generally composed of quartz, feldspars and micas. Feldspars are changed to clay minerals such as kaolinite and illite after weathering process. Biotite of mica produce iron oxides which induce color changes on surface of rocks. The experiments were conducted using field spectrometer FieldSpec®3 of ASD Inc. and the range of measurement was form 350µm to 2500µm wavelength. Spectral reflectance of weathering products at each measuring point was processed by removing delineated convex hull from raw reflectance curves to exclude background effects and to extract quantitative absorption depths which indicate relative distribution degree of weathering products. We produced deterioration map on the surface of the monument by interpolating absorption depth values of each point with consideration of spatial distribution of measurements. For facilitation of practical uses a chain of working process of this method was designed using whole experimental processes.