Dongok Ryu

Development of a program for toric intraocular lens calculation considering posterior corneal astigmatism, incision-induced posterior corneal astigmatism, and effective lens position

BackgroundTo evaluate the toric intraocular lens (IOL) calculation considering posterior corneal astigmatism, incision-induced posterior corneal astigmatism, and effective lens position (ELP).MethodsTwo thousand samples of corneal parameters with keratometric astigmatism ≥ 1.0 D were obtained using bootstrap methods. The probability distributions for incision-induced keratometric and posterior corneal astigmatisms, as well as ELP were estimated from the literature review. The predicted residual astigmatism error using method D with an IOL add power calculator (IAPC) was compared with those derived using methods A, B, and C through Monte-Carlo simulation. Method A considered the keratometric astigmatism and incision-induced keratometric astigmatism, method B considered posterior corneal astigmatism in addition to the A method, method C considered incision-induced posterior corneal astigmatism in addition to the B method, and method D considered ELP in addition to the C method. To verify the IAPC used in this study, the predicted toric IOL cylinder power and its axis using the IAPC were compared with ray-tracing simulation results.ResultsThe median magnitude of the predicted residual astigmatism error using method D (0.25 diopters [D]) was smaller than that derived using methods A (0.42 D), B (0.38 D), and C (0.28 D) respectively. Linear regression analysis indicated that the predicted toric IOL cylinder power and its axis had excellent goodness-of-fit between the IAPC and ray-tracing simulation.ConclusionsThe IAPC is a simple but accurate method for predicting the toric IOL cylinder power and its axis considering posterior corneal astigmatism, incision-induced posterior corneal astigmatism, and ELP.

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.

Sun-, Earth- and Moon-integrated simulation ray tracing for observation from space using ASAP

The Space Optics Laboratory at Yonsei University, Korea, in cooperation with Breault Research Organization (BRO) in Tucson, Arizona, have invested significant research and development efforts into creating large scale ray tracing techniques for simulating “reflected” light from the earth with an artificial satellite. This presentation describes a complex model that combines the sun, the earth and an orbiting optical instrument combined into a real scale nonsequential ray tracing computation using BRO’s Advanced Systems Analysis Program, ASAP®. The Sun is simulated as a spherically emitting light source of 695,500 km in diameter. The earth also is simulated as a sphere with its characteristics defined as target objects to be observed and defined with appropriate optical properties. They include the atmosphere, land and ocean elements, each having distinctive optical properties expressed by single or combined characteristics of refraction, reflection and scattering. The current embodiment has an atmospheric model consisting of 33 optical layers, a land model with 6 different albedos and the ocean simulated with sun glint characteristics. A space-based optical instrument, with an actual opto-mechanical prescription, is defined in an orbit of several hundreds to thousands of miles in altitude above the earth’s surface. The model allows for almost simultaneous evaluations of the imaging and radiometric performances of the instrument. Several real-life application results are reported suggesting that this simulation approach not only provides valuable information that can greatly improve the space optical instrument performance but also provides a simulation tool for scientists to evaluate all phases of a space mission.

Integrated ray tracing simulation of annual variation of spectral bio-signatures from cloud free 3D optical Earth model

Understanding the Earth spectral bio-signatures provides an important reference datum for accurate de-convolution of collapsed spectral signals from potential earth-like planets of other star systems. This study presents a new ray tracing computation method including an improved 3D optical earth model constructed with the coastal line and vegetation distribution data from the Global Ecological Zone (GEZ) map. Using non-Lambertian bidirectional scattering distribution function (BSDF) models, the input earth surface model is characterized with three different scattering properties and their annual variations depending on monthly changes in vegetation distribution, sea ice coverage and illumination angle. The input atmosphere model consists of one layer with Rayleigh scattering model from the sea level to 100 km in altitude and its radiative transfer characteristics is computed for four seasons using the SMART codes. The ocean scattering model is a combination of sun-glint scattering and Lambertian scattering models. The land surface scattering is defined with the semi empirical parametric kernel method used for MODIS and POLDER missions. These three component models were integrated into the final Earth model that was then incorporated into the in-house built integrated ray tracing (IRT) model capable of computing both spectral imaging and radiative transfer performance of a hypothetical space instrument as it observes the Earth from its designated orbit. The IRT model simulation inputs include variation in earth orientation, illuminated phases, and seasonal sea ice and vegetation distribution. The trial simulation runs result in the annual variations in phase dependent disk averaged spectra (DAS) and its associated bio-signatures such as NDVI. The full computational details are presented together with the resulting annual variation in DAS and its associated bio-signatures.

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.

Effective treatment of a injected hyaluronic acid-induced Tyndall effect with a 1064-nm Q-switched Nd:YAG laser

after appearance. There was no history of exposure to ultraviolet radiation or heat application and she did not use any cosmetics on her body. On physical examination, pigmented brownish macules with a smooth surface, which had become confluent, forming pigmented patches with a reticular pattern on the scalp, lateral aspect of the face, preauricular region, neck, trunk, abdomen, groin, and the proximal regions of the arms and legs, were seen (Fig. 1). In some areas, there were pink or violet, slightly raised, shiny papules. There was no oral or nail involvement. Routine laboratory investigations were normal. The patient did not use drugs, was euthyroid and had no blood markers of lupus erythematosus. Histopathological examination of a biopsy taken from a papular lesion showed the typical features of lichen planus (LP). Histological examination of the macular lesions showed epidermal atrophy, pigment incontinence and apoptotic keratinocytes in the epidermal basal layer (Fig. 2). The papular lesions, consistent with LP, gradually disappeared with systemic corticosteroid treatment within 4 weeks but the LPP lesions persisted over 6 months of follow-up. LPP is a condition of unknown aetiology exhibiting dark brown macules and ⁄ or papules and a long clinical course without pruritus or any scalp, nail or mucosal involvement. Cell-mediated immunity seems to play a role in triggering the disease. Pigmentation is mostly diffuse or reticular in pattern. The diffuse form is the commonest type of pigmentation, with the reticular and perifollicular patterns being less comman. Rarely. involvement can be generalized as in our patient. Our patient had generalized and mostly symmetrical lesions on the scalp, neck, body and upper areas of the limbs . The scalp involvement was interesting because it is very rare in this type of LPP. In conclusion, this case is an unusual form of LPP with scalp involvement, accompanied by LP and lichen planopilaris. LPP is mainly seen in the Indian population, but recently some cases of white and Japanese origin have been described. To our knowledge, this is the first case reported from Turkey.

Ring-shaped dysphotopsia associated with posterior chamber phakic implantable collamer lenses with a central hole

To evaluate the incidence of central hole‐induced ring‐shaped dysphotopsia after posterior chamber phakic implantable collamer lens (ICL) with central hole (hole ICL) implantation and to investigate the causes of central hole‐induced dysphotopsia.

Design of a laboratory testbed for external occulters at flight Fresnel numbers

One of the main candidates for creating high-contrast for future Exo-Earth detection is an external occulter or sharshade. A starshade blocks the light from the parent star by flying in formation along the line-of-sight from a space telescope. Because of its large size and scale it is impossible to fully test a starshade system on the ground before launch. Instead, we rely on modeling supported by subscale laboratory tests to verify the models. At Princeton, we are designing and building a subscale testbed to verify the suppression and contrast of a starshade at the same Fresnel number as a flight system, and thus mathematically identical to a realistic space mission. Here we present the mechanical design of the testbed and simulations predicting the ultimate contrast performance. We will also present progress in implementation and preliminary results.

Improved atmospheric 3D BSDF model in earthlike exoplanet using ray-tracing based method

The studies on planetary radiative transfer computation have become important elements to disk-averaged spectral characterization of potential exoplanets. In this paper, we report an improved ray-tracing based atmospheric simulation model as a part of 3-D earth-like planet model with 3 principle sub-components i.e. land, sea and atmosphere. Any changes in ray paths and their characteristics such as radiative power and direction are computed as they experience reflection, refraction, transmission, absorption and scattering. Improved atmospheric BSDF algorithms uses Q.Lius combined Rayleigh and aerosol Henrey-Greenstein scattering phase function. The input cloud-free atmosphere model consists of 48 layers with vertical absorption profiles and a scattering layer with their input characteristics using the GIOVANNI database. Total Solar Irradiance data are obtained from Solar Radiation and Climate Experiment (SORCE) mission. Using aerosol scattering computation, we first tested the atmospheric scattering effects with imaging simulation with HRIV, EPOXI. Then we examined the computational validity of atmospheric model with the measurements of global, direct and diffuse radiation taken from NREL(National Renewable Energy Laboratory)s pyranometers and pyrheliometers on a ground station for cases of single incident angle and for simultaneous multiple incident angles of the solar beam.