Picture and reflectance spectra of samples used in this study. Panel a: sample images: from left to right, the four columns are PLG, ILM, OPX, and OLV samples with different particle sizes, respectively. Samples in the same row have the same size distribution; for instance, the four samples in the top row all have a size distribution of <45 μm. Panel b: reflectance spectra of the four mineral samples with a particle size distribution of 61–74 μm measured at i = 30°, e = 0°, g = 30°. The dashed lines indicate the central wavelengths of the four filters used in this study. The inset plot shows the enlarged view of the ILM spectrum, which has a reflectance peak around 850 nm.