A mid-infrared spectroscopic imager needs to be portable and tough for the identification of dyestuffs used for murals in ancient tombs during archaeological on-site analysis. Meanwhile, an extremely compact and tough hyperspectral camera with mass less than 2 kg is required for mounting on drones to observe nutritive components like nitrogen and phosphorus. We proposed a near-common-path wavefront-division phase-shift interferometer as an imaging-type twodimensional Fourier spectrometer. Because the proposed interferometer has strong robustness against mechanical vibrations, a palm-sized Fourier spectroscopic imager can be realized without an anti-mechanical vibration system. We developed a palm-sized (80-mm cube weighing 0.5 kg) and tough hyperspectral camera for mid-infrared light (wavelength of 8–14 μm) that can be operated using only a notebook personal computer. Furthermore, the field of view of a conventional hyperspectral camera is narrow (e.g., 6.4 deg × 5.1 deg). However, employing a proposed field angle correlation method and using a fisheye lens as the objective lens, the field of view can be expanded to 180 deg. The total price of the mid-infrared two-dimensional spectroscopic imager is no more than several thousand USD because a lowprice microbolometer (Vision Sensing, VIM-80G2, wavelength range: 8-14 μm, 80 × 80 pixels, price: 300 USD) is used. Additionally, a long-stroke (10 mm) and high-resolution (Optical encoder resolution: 100 nm) impact-drive actuator (Technohands XCWT70-10 weighing 30 g) is introduced as a low-price (1000 USD) and tough phase-shift stage with cross-roller linear-motion guides.
High-frequency spectroscopic observation methods using small satellites and drones for monitoring of plankton in the ocean and vegetation activity have recently attracted considerable attention. However, in multi-directional spectroscopic imaging, the spectroscopic characteristics vary depending on the observation and illumination angles. Therefore, huge quantities of spectroscopic data were previously required for every conceivable combination of zenith and azimuth angles to identify plant species. The method proposed here can identify any plant species from near-surface and internal reflectance spectroscopic data, regardless of the zenith and azimuth angles. We assume that the observed spectral intensity can be calculated as a linear sum of the near-surface spectral reflectivity and the internal diffusion spectral reflectivity multiplied by the light-source spectral intensity and the reflection correction coefficients a and b. We acquire the near-surface and internal reflected light as basic spectroscopic data using the orthogonal polarized light illumination method. The coefficients a and b can be calculated from basic spectroscopic data. We obtain m-sets (ai, bi) (i =1-m) using combinations of the numbers of λ1…λn. If the reflection correction coefficient of the m-sets (ai, bi) is close to one, we identify the observed plant as a plant species contained in the basic data. If the two species are different, the m-sets (ai, bi) have uncorrelated values and the m-sets (ai, bi) reflection correction coefficient decreases towards zero. In this work, we performed feasibility demonstrations using two types of plant and successfully determined from the basic data that the observed plant is the correct plant species.
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