Soomin Jeong

In-orbit imaging and radiometric performance prediction for flight model Geostationary Ocean Color Imager

The Geostationary Ocean Colour Imager (GOCI) is a visible band ocean colour instrument onboard the Communication, Ocean, and Meteorological Satellite (COMS) scheduled to be in operation from early 2010. The instrument is designed to monitor ocean water environments around the Korean peninsula in high spatial and temporal resolutions. We report a new imaging and radiometric performance prediction model specifically designed for GOCI. The model incorporates the Sun as light source, about 4000km x 4000km section of the Earth surrounding the Korean peninsula and the GOCI optical system into a single ray tracing environment in real scale. Specially, the target Earth section is constructed using high resolution coastal line data, and consists of land and ocean surfaces with reflectivity data representing their constituents including vegetation and chlorophyll concentration. The GOCI instrument in the IRT model is constructed as an optical system with realistic surface characteristics including wave front error, reflectivity, absorption, transmission and scattering properties. We then used Monte Carlo based ray tracing computation along the whole optical path starting from the Sun to the final detector plane, for simultaneous imaging and radiometric performance verification for a fixed solar zenith angle. This was then followed by simulation of red-tide evolution detection and their radiance estimation, in accordance with the in-orbit operation sequence. The simulation results prove that the GOCI flight model is capable of detecting both image and radiance originated from the key ocean phenomena including red tide. The model details and computational process are discussed with implications to other earth observation instruments.

Integrated ray tracing simulation of spectral bio-signatures from full 3D earth model

Accurate identification and understanding of spectral bio-signatures from possible extra terrestrial planets have received an ever increasing attention from both astronomy and space science communities in recent years. In pursuance of this subject, one of the most important scientific breakthroughs would be to obtain the detailed understanding on spectral biosignatures of the Earth, as it serves as a reference datum for accurate interpretation of collapsed (in temporal and spatial domains) information from the spectral measurement using TPF instruments. We report a new Integrated Ray Tracing (IRT) model capable of computing various spectral bio-signatures as they are observed from the Earth surface. The model includes the Sun, the full 3-D Earth, and an optical instrument, all combined into single ray tracing environment in real scale. In particular, the full 3-D Earth surface is constructed from high resolution coastal line data and defined with realistic reflectance and BSDF characteristics depending on wavelength, vegetation types and their distributions. We first examined the model validity by confirming the imaging and radiometric performance of the AmonRa visible channel camera, simulating the Earth observation from the L1 halo orbit. We then computed disk averaged spectra, light curves and NDVI indexes, leading to the construction of the observed disk averaged spectra at the AmonRa instrument detector plane. The model, computational procedure and the simulation results are presented. The future plan for the detailed spectral signature simulation runs for various input conditions including seasonal vegetation changes and variable cloud covers is discussed.

In-orbit image performance simulation for GOCI from integrated ray tracing computation

Geostationary Ocean Color Imager(GOCI) is one of three payloads on board the Communication, Ocean, and Meteorological Satellite(COMS) launched 27th, June, 2010. For understanding GOCI imaging performance, we constructed the Integrated Ray Tracing model consisting of the Sun model as a light source, a target Earth model, and the GOCI optical system model. We then combined them in Monte Carlo based ray tracing computation. Light travels from the Sun and it is then reflected from the Earth section of roughly 2500km * 2500km in size around the Korea peninsula with 40km in spatial resolution. It is then fed into the instrument before reaching to the detector plane. Trial simulation runs for the GOCI imaging performance were focused on the combined slot images and MTF. First, we used modified pointing mirror mechanism to acquire the slot images, and then mosaiced them. Their image performance from the GOCI measurement were compared to the ray tracing simulation results. Second, we investigated GOCI in-orbit MTF performance with the slanted knife edge method applied to an East coastline image of the Korea peninsula covering from 38.04N, 128.40E to 38.01N, 128.43E. The ray tracing simulation results showed 0.34 in MTF mean for near IR band image while the GOCI image obtained 9th Sep, 2010 and 15th Sep, 2010, were used to produce 0.34 at Nyquist frequency in MTF. This study results prove that the GOCI image performance is well within the target performance requirement, and that the IRT end-to-end simulation technique introduced here can be applicable for high accuracy simulation of in-orbit performances of GOCI and of other earth observing satellite instruments.

Measurement of Cosmic-Ray Nuclei with the Third Flight of the CREAM Balloon-Borne Experiment

The balloon-borne Cosmic Ray Energetics And Mass experiment had its third flight (CREAM-III) over Antarctica for 29 days from December 17, 2007 to January 19, 2008. CREAM-III was designed to directly measure the elemental spectra of cosmic-ray nuclei from Hydrogen to Iron in the energy range from 10^12 to 10^15 eV. Energy of incident cosmic rays was measured with a calorimeter that consisted of a densified carbon target directly above a stack of 20 alternating layers of tungsten and scintillating fiber ribbons. Multiple charge measurements were independently made with the silicon charge detector (SCD), Cherenkov Camera (CherCam), and a Timing Charge Detector (TCD) in order to identify particles and minimize backscattering effects from the calorimeter. Compared to previous CREAM flights, the electronic noise of CREAM-III was reduced, significantly lowering the energy threshold. Results from on-going analysis of the energy spectra will be presented.

Boron And Carbon Cosmic rays in the Upper Stratosphere (BACCUS)

The balloon-borne BACCUS experiment measures directly the elemental spectra of cosmic-ray nuclei from protons to Fe over the energy range ~10^12 to 10^15 eV. It focuses on the energy dependence of secondary to primary ratios (e.g. B/C) to investigate cosmic-ray propagation history. BACCUS consists of redundant and complementary particle detectors including the Timing Charge Detector (TCD), Transition Radiation Detector (TRD), Cherenkov Detector (CD), Silicon Charge Detector (SCD), and Calorimeter (CAL). The TCD measures the light yield produced by the particle in plastic scintillator. The TRD provides energy measurements of incident 3 ≤ Z ≤ 26 nuclei in the 102 – 105 Lorentz factor range. The CD responds only to particles with velocity exceeding the velocity of light in the plastic. It allows BACCUS to reject the abundant low energy cosmic rays present in the polar region. The CAL is used to determine the particle’s energy for all nuclei for 1 ≤ Z ≤ 26. With the SCD based on pixellation, in addition to the TCD based on timing, and the CD, the BACCUS instrument implements virtually all possible techniques to minimize the effect of backscatter on charge measurements in the presence of a large particle shower in the CAL. The 30 day flight was carried out successfully over Antarctica in 2016 from Nov. 28 to Dec. 28. The integration test, and performance of instruments will be presented.

The Slewing Mirror Telescope of UFFO-Pathfinder: first performance report in space

The Slewing Mirror Telescope(SMT) is the first orbital instrument, using motorized mirror for observations of the space, designed to shed light on first seconds of Gamma-Ray Bursts (GRBs) prompt UV/optical emission. The SMT is main component of the Ultra-Fast Flash Observatory (UFFO). Once GRB is detected by UFFO X-ray coded mask camera, SMT turns its motorized mirror within seconds to observe optical and UV emission of GRB. After several years of delay on its launch, UFFO was finally launched in 28 April 2016. Launch took place onboard Lomonosov satellite from new Russian kosmodrom Vostochny. Several space tests have been performed during that period, which proved the concept of SMT and gave precise values of SMT sensitivity and resolution. For the first time in the space observations, motorized mirror system is able to trace objects despite the drift of telescope FOV due to satellite orbital movement.

Measurements of the Proton and Helium Spectra from CREAM-V

The Cosmic Rays Energy And Mass (CREAM) balloon payload directly measures the composition and elemental spectra of cosmic rays in the upper stratosphere. It is designed to probe the acceleration mechanism and propagation history of cosmic rays at energies from 10

The Cosmic Ray Energetics And Mass for the International Space Station (ISS-CREAM) Instrument

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Performance of the ISS-CREAM Calorimeter

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Performance of the BACCUS Transition Radiation Detector

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