Jinsuk Hong

Stray light analysis of nearby slot source using integrated ray tracing technique

In the remote sensing researches, the reflected bright source from out of FOV has effects on the image quality of wanted signal. Even though those signal from bright source are adjusted in corresponding pixel level with atmospheric correction algorithm or radiometric correction, those can be problem to the nearby signal as one of the stray light source. Especially, in the step and stare observational method which makes one mosaic image with several snap shots, one of target area can affect next to the other snap shot each other. Presented in this paper focused on the stray light analysis from unwanted reflected source for geostationary ocean color sensor. The stray light effect for total 16 slot images to each other were analyzed from the unwanted surrounding slot sources. For the realistic simulation, we constructed system modeling with integrated ray tracing (IRT) technique which realizes the same space time in the remote sensing observation among the Sun, the Earth, and the satellite. Computed stray light effect in the results of paper demonstrates the distinguishable radiance value at the specific time and space.

Marked hydroureter misdiagnosed as a hydrosalpinx by ultrasound.

The retroperitoneal space of the posterior abdomen and the pelvic retroperitoneum contain the major neural, vascular and lymphatic supply to the pelvic viscera, the urinary system and colorectal system. A pain or mass in the pelvis may arise primarily from the reproductive organs, but it may just as easily arise from the retroperitoneal space, include the urinary tract and the gastrointestinal tract. Therefore, the gynecologic surgeon should be aware of the various conditions associated with retroperitoneal mass and the correct management of these disorders. Hydroureter may misdiagnose as a pelvic mass or retroperitoneal mass. The cause of hydroureter is mainly secondary obstruction such as malignancy, idiopathic retroperitoneal fibrosis and pelvic disease but primary obstructive megaureter should be considered. This report describes a case of marked hydroureter, misdiagnosed as a hydrosalpinx by ultrasound.

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.

Novel orthogonal velocity polishing tool and its material removal characteristics from CVD SiC mirror surfaces

A new and patented polishing tool called Orthogonal Velocity field Tool (OVT) was built and its material removal characteristics from Chemical Vapor Deposition Silicon Carbide (CVD SiC) mirror surfaces were investigated in this study. The velocity field of OVT is produced by rotating the bicycle type tool in the two orthogonal axes, and this concept is capable of producing a material removal foot print of pseudo Gaussian shapes. First for the OVT characterization, we derived a theoretical material removal model using distributions of pressure exerted onto the workpiece surface, relative speed between the tool and workpiece surface, and dwell time inside the tool- workpiece contact area. Second, using two flat CVD SiC mirrors that are 150 mm in diameter, we ran material removal experiments over machine run parameter ranging from 12.901 to 25.867 psi in pressure, from 0.086 m/sec to 0.147 m/sec tool in the relative speed, and 5 to 15 sec in dwell time. Material removal coefficients are obtained by using the in-house developed data analysis program. The resulting material removal coefficient varies from 3.35 to 9.46 um/psi hour m/sec with a mean value of 5.90 ± 1.26(standard deviation). We describe the technical details of the new OVT machine, the data analysis program, the experiments, and the results together with the implications to the future development of the machine.

Imaging and radiometric performance simulation for a new high-performance dual-band airborne reconnaissance camera

In recent years, high performance visible and IR cameras have been used widely for tactical airborne reconnaissance. The process improvement for efficient discrimination and analysis of complex target information from active battlefields requires for simultaneous multi-band measurement from airborne platforms at various altitudes. We report a new dual band airborne camera designed for simultaneous registration of both visible and IR imagery from mid-altitude ranges. The camera design uses a common front end optical telescope of around 0.3m in entrance aperture and several relay optical sub-systems capable of delivering both high spatial resolution visible and IR images to the detectors. The camera design is benefited from the use of several optical channels packaged in a compact space and the associated freedom to choose between wide (~3 degrees) and narrow (~1 degree) field of view. In order to investigate both imaging and radiometric performances of the camera, we generated an array of target scenes with optical properties such as reflection, refraction, scattering, transmission and emission. We then combined the target scenes and the camera optical system into the integrated ray tracing simulation environment utilizing Monte Carlo computation technique. Taking realistic atmospheric radiative transfer characteristics into account, both imaging and radiometric performances were then investigated. The simulation results demonstrate successfully that the camera design satisfies NIIRS 7 detection criterion. The camera concept, details of performance simulation computation, the resulting performances are discussed together with future development plan.

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.

Assembly and alignment method for optimized spatial resolution of off-axis three-mirror fore optics of hyperspectral imager

A fore optics for the hyperspectral spectrometer is designed, manufactured, assembled, and aligned. The optics has a telecentric off-axis three-mirror configuration with a field of view wider than 14 degrees and an f-number as small as 2.3. The primary mirror (M1) and the secondary mirror (M2) are axially symmetric aspheric surfaces to minimize the sensitivity. The tertiary mirror (M3) is a decentered aspheric surface to minimize the coma and astigmatism aberration. The M2 also has a hole for the slit to maintain the optical performance while maximizing the telecentricity. To ensure the spatial resolution performance of the optical system, an alignment procedure is established to assemble and align the entrance slit of the spectrometer to the rear end of the fore optics. It has a great advantage to confirm and maintain the alignment integrity of the fore optics module throughout the alignment procedure. To perform the alignment procedure successfully, the precision movement control requirements are calculated and applied. As a result, the alignment goal of the RMS wave front error (WFE) to be smaller than 90 nm at all fields is achieved.

Backward reflection analysis of transmitting channel of active laser ranging optics

The designed Active LDR(Laser Detection and Ranging) System contains high-power Laser and its diameter is approximately 24mm. Although the laser transmitting channel and receiving optic channel are completely separated from each other and doesn’t share any of the optical components in design, each channel shares 4 wedge scanners, which are to overcome the narrow FOV(Field of View) of the optical system. Any backward reflection back to the fiber laser end must be carefully studied since it can damage the LD(Laser Diodes), the inner components of the laser unit because of the high amplification factor of the laser unit. In this study, the stray light caused by the transmitting channel’s laser and inner reflection by optical components were analyzed by ASAP(Advanced System Analysis Program) software. We also can confirm the operability and stability of the system by more than 6 months of operation of the system.

Ray tracing based simulation of stray light effect for geostationary ocean color imager

Image mosaic technique is widely used in a field of remote sensing research. However, in case of Geostationary Ocean Color Imager’s (GOCI’s) mosaic image which is consist of 16 slot images, the radiance level discrepancy was noticed in the cloudy circumstance next to each other slot when acquiring the imagery data in the low Sun elevation angle. We provided, in this study, the in-depth stray light analysis results in order to find out this discrepancy phenomenon, and performed to compare the stray light pattern via a bright target movement. Stray light analysis as the first step was completed with ray tracing technique based on ASAP program, and we suggested that unwanted radiations from the Earth bright target or the atmosphere such as cloud are major candidates of stray light in the problematic images. For embodying GOCI operational concept, 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. In the second step, we investigated the stray light pattern at each slot image including unwanted random source from out of field, and then constructed the simulated mosaic bias image reached at the detector plane. In the simulated bias, the ray path followed the procedures that 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 16 slots. Lastly, we analyzed stray light pattern in the third step for the real image environment acquired at UTC-03 16th, October, 2011. In addition, verification was performed to compare the difference among slot boundaries for moving bright target.

Laboratory test simulation for non-flat response calibration of global Earth albedo monitor

In this report, we present laboratory test simulation for directional responsivity of a global Earth albedo monitoring instrument. The sensor is to observe the Sun and the Earth, alternately, and measure their shortwave (<4μm) radiations around the L1 halo orbit to obtain global Earth albedo. The instrument consists of a broadband scanning radiometer (energy channel instrument) and an imager (visible channel instrument) with ±2° field-of-view. In the case of the energy channel instrument, radiations arriving at the viewing ports from the Sun and the Earth are directed toward the pyroelectric detector via two spherical folding mirrors and a 3D compound parabolic concentrator (CPC). The instrument responsivity is defined by the ratio of the incident radiation input to the instrument output signal. The radiometer’s relative directional responsivity needs to be characterized across the field-of-view to assist output signal calibration. For the laboratory test, the distant small source configuration consists of an off-axis collimator and the instrument with adjustable mounts. Using reconstructed 3D CPC surface, the laboratory test simulation for predicting the instrument directional responsivity was conducted by a radiative transfer computation with ray tracing technique. The technical details of the laboratory test simulation are presented together with future plan.