A proto-model of an off-axis reflective fore-optics in a new hyperspectral sensor onboard a small unmanned aerial vehicle (UAV) is developed for low-altitude coastal remote sensing. In spite of the substantial advantages of off-axis optics over refractive or on-axis reflective optics, it is difficult to fabricate and align the mirrors in off-axis systems because of their asymmetric configurations. The fore-optics is designed by Korea Institute of Ocean Science & Technology (KIOST) as a three-mirror system including aspheric primary and secondary mirrors, with an entrance pupil diameter of 70 mm and F-ratio of 5.0. The off-axis mirror is fabricated by a single point diamond turning machine (SPDTM) with a form accuracy of 89.3 nm (RMS) and surface roughness of 7.2 nm (Ra). Coarse alignment of this three-mirror off-axis optical system is accomplished by using a designated base plate and a coordinate measuring machine. The optical performance is tested using the point spread function of the returned collimated beam of a Fizeau interferometer.
This study proposes a newly developed dry washing method for removing pollutants such as total petroleum hydrocarbon (TPH) and oxidized iron from the surface of ballast gravel. A batch-type dry washing method showed a good performance in a previous study. In this study, a continuous-type dry washing system, instead of a batch-type system, was prepared to improve the efficiency of the system. A drier and a separator were also applied to this system as pre-treatment process, and the performance of this system was evaluated. In this experiment, blasting media was blasted on the polluted gravels through 12 nozzles by a pressure of 5-6kg/cm 2 for 20-30 mins to remove TPH and oxidized iron. It was found to be possible to remove 80-90% of TPH and oxidized iron by using this system. Several ways to improve the performance were suggested in this study.
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