Surface Weathering Degree Mapping for Granite Using Reflectance Spectroscopy2. Weathering Characteristics of Mt. Gwanak Granite Granite of Mt. Gwanak is biotite granite (Kwon et al., 1995). Its constituents are quartz, feldspar and mica, especially biotite. Hardness and durability of quartz are greater than other granite forming minerals and quartz has no diagnostic peak in spectral reflectance curves. Feldspar and mica produce clay minerals, such as illite and kaolinite, according to weathering processes. Spectral reflectance curves of granite constituents have no diagnostic absorption peaks except for microcline in the vicinity of 2.2? wavelength. Spectral reflectance curves of clay minerals show strong absorption peak in the vicinity of 2.2? wavelength (Clark et al., 2003). 3. Surface Weathering Degree Assessment of Granite Field spectrometer (Fieldspec®3) was used to measure surface reflectance curves of granite specimens. The prove of 25 degree FOV (field of view) was applied to measure reflectances of three specimens and two types of target area, circles of 1cm and 2cm diameter, were set up (Fig. 1).  Fig. 1. Target areas for measurement of spectral reflectances. The diameter of big spot is about 2cm and the diameter of small spot is about 1cm. 4. Results Spectral reflectances of weathered granite surface were measured and continuum removal step was processed (Fig. 2) to remove background absorptions and extract inherent absorption features (Clark and Roush, 1984; Kruse et al., 1985). Quantitative comparison among weathered specimens was derived using absorption feature and its depth of 2.2? wavelength in the continuum removed curves (Table 1).  Fig. 2. Raw spectral reflectance curves and continuum removed spectral reflectance curves of weathered granite specimens from S1 to S3. |