A Hyperspectral Camera Track System for Automating Diffuse Color Reflectance Measurements of Drill Cores

Diffuse reflectance spectrophotometry is a technique used to identify lithological changes of drill cores by measuring variations in spectral reflection along split-core surfaces and normalizing to a pure reflecting standard. In addition to supporting core description, the method has been useful as a proxy for carbonate content and semi-quantitative analysis of components such as iron oxides, clays and organic matter. Accurate spectral data is crucial for determining color reflectance. Currently, the International Ocean Discovery Program (IODP) uses an Ocean Insight QE-Pro spectrometer to make contact measurements on core surfaces and provide bulk color reflectance at regular intervals of 1 to 5 cm. To prevent the sensor from contamination with sediment, the core sections are covered with a thin layer of transparent polyethylene film, which in-house testing has shown to have a non-negligible effect to the low wavelength visible spectral response. We present a new contactless hyperspectral track system in development at IODP with a spectral range of 380-1020 nm (bandwidth 1-1.14 nm). The new system provides full spectral data for each pixel imaged, for pixels of ~64 micron size. Core sections of up to 150 cm are scanned with a Resonon Pika-L hyperspectral pushbroom-style camera mounted on the movable head of an in-house constructed track system. Lighting is supplied by two customized Prophotonix COBRA Hyperspec LED line lights with enhanced spectral power distribution emphasizing the low-visible range and positioned to reduce shadowing across coarse material. Measurements are orchestrated via an in-house LabView application to control the track system and coordinate data acquisition, and an in-house Python application to perform data reduction of the hyperspectral datacubes. Color reflectance data are generated by performing a flat-field correction of each datacube and converting the spectral reflectance within the visible range to CIE Tristimulus XYZ color space. Additional color space values RGB, L*a*b*, and Munsell color are further derived from XYZ values. We present the progress of IODP in implementing the new hyperspectral logger (HYPERSCAN) and assess its ability to overcome spectral artifacts that degraded previous reflectance measurements made by IODP.