Development of portable, visible to infra-red spectrometer to measure geophysical and geochemical properties of rocks

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In this research, we developed portable, visible to near infra-red spectrometer (Geosensor) which is 228x308x172 mm in size, 8 kg in weight, possessing its own light source, and capable of measuring reflection intensity over the wide wave length ranging from 400 nm to 2500 nm within 8 seconds with the resolution of less than 6 nm. The first year was spent almost entirely to construct the instrument. Tests both in the laboratory and in the field (out-door) were repeated to evaluate its precision, reproducibility, and other specification and to improve its usability to meet our requirements. Although the reproducibility within the wave range of 400 to 700 nm and 2400 to 2500 nm was not good enough, its resolution and reproducibility was both acceptable in the wave range of 700 to 2400 nm. From the later half of the second year to the third year, we moved to the next step to explore its applicability in the field geoscience. First, we measured reflective spectra for various rock types, an … More d found that Geosensor is capable of identifying broad absorb peaks situated at 550 nm and 900 nm attributable to Fe^<3+>, broad absorb peak situated at 1100 nm attributable to Fe^<2+>, relatively sharp absorb peaks at 1400 and 1900 nm attributable to water, sharp peaks situated at 1400,2200, and 2450 nm attributable to -OH,and sharp peak situated at 2350 nm attributable to CO3^<2->. Next we experimentally examined the controlling factors which influence the intensity of the absorb peak (absorbance) of water. The result suggests that the absorbance is mainly controlled by such factors as water content, grain size, and contents of opaque grains. The result further suggests that if we restrict the rock type as fine grained sediments with relatively similar water contents, we can estimate contents of opaque grains based on quick measurements by Geosensor. We applied this method to actual sediment core samples recovered from Japan Sea to estimate organic carbon and pyrite contents and obtained satisfactory result. Less