• The Journal of Engineering Geology
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• v.29 no.2
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• pp.153-162
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• 2019

Rapid variations in the geometry (i.e., thickness) of the refractor and low velocities affect greatly the imaging of the reflectors of land seismic data. Conventional solutions to obtain the weathering models utilizes first break picking method, which requires time consuming steps and causes the human error in picking the first arrivals. A new interferometric approach (interferometric refraction statics, IRS) which utilizes the first arrival signal (S/N enhanced by refraction convolution stack) instead of first break picking, is tested in this study to the synthetic data from the velocity structure provided by surface geophysics (refraction, MASW) and borehole geophysics (tomography, SPS logging) for the Cheongju granitic bodies. The results of IRS approach are found to be better than the ones from conventional first break picking in terms of continuities and horizontal resolution of the reflectors. The unresolved long-wavelength statics in brute stack are much removed by IRS weathering correction and the overlying refractors (the base of shallow weathering zone) are incidentally delineated in the refraction convolution stack.

• Journal of Korean Ophthalmic Optics Society
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• v.11 no.4
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• pp.345-350
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• 2006

The study of the visual acuity and refraction status was performed to the students of primary school using eyeglasses in Kyung Nam region, Korea. Two hundred sixty three subjects with various styles of ametropia were analyzed the visual acuity and refraction examination by the subjective and objective tools. The results of study were as follows; 1) According to the increase of age of subjects, the visual acuity of binocular in naked eyes was decrease. However ametropia was increase. 2) The high frequency of ametropia types in the binocular was simple myopia, and the next order of high frequency was mixed astigmatism, myopic compound astigmatism, simple hyperopia, and hyperopic compound, respectively. 3) On the power of spherical refractive error of ametropia, the high frequency was -1.00 diopter, and the next order of high frequency was -2.00 diopter, +2.00 diopter, -3.00 diopter, and so on, respectively. 4) According to the increase of subjects ages, the changes of dioptric power of myopic spheric power was increase. however the frequency of the boy and girl was similar results, also the dioptric values of refractive status in binocular was similar results. As the results of this study, we conclude that the relationship of the visual acuity and refractive error status in primary students using eyeglasses was improved.

• Journal of Korean Clinical Health Science
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• v.2 no.3
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• pp.203-208
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• 2014

Purpose. To analysis the refractive error in 7-9 year-old Korea children. Methods. From July 2013 to June 2014, two hundred eighty two subjects were performed in refraction test using the Auto-Refractometry. Results. The refractive error by spherical equivalent among all subjects was myopia 47.58%, emmetropia 42.35%, astigmatism 32.33%, and hyperopia 8.76%. Myopia was more common in female than males although the difference was not statically significant. The axis of astigmatism was with the rule in 65%, against the rule in 31.5%, and oblique in 3.5% There was a statistical significance between 7 year and 9 year of male in the spherical equivalent power(p=0.010). Also there was a statistical significance between 7 years and 9 years of female in the spherical equivalent power(p=0.036). However, there was not a statistical significance between male and female in spherical equivalent power(p>0.5). Conclusions. In this study, myopia was the most common refractive error. On the other hand, The prevalence of the axis of astigmatism was the with- the- rule. The spherical equivalent of refractive error was similar results between male and female. However The refractive error was different style with aging. these data suggested that the analysis of the refractive error at young children can provide the information of useful diagnosis for the correction of visual acuity.

• Proceedings of the KIEE Conference
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• 2007.10a
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• pp.225-226
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• 2007

In the semiconductor manufacturing industry, the heterodyne laser interferometer plays as an ultra-precise measurement system. However, the heterodyne laser interferometer has some unwanted environmental error which is caused from refraction in the air. This is an obstacle to improve the measurement accuracy in nanometer scale. In this paper we propose a compensation algorithm based on Data Fusion method which reduces the environmental error in the heterodyne laser interferometer. Through some experiments, we demonstrate the effectiveness of the proposed algorithm in measurement accuracy.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.4
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• pp.642-649
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• 2010

LOS analysis is used for optimal deployment of mid-range guided weapon system or system engagement effectiveness simulation. Comparing to real-world, LOS analysis includes error sources such as coarse terrain data resolution, refraction of radio waves, and several ideal assumptions. In this research, exact LOS algorithm under assumption of constant earth curvature and error analysis of that is investigated. It proved that LOS algorithm under assumption of constant earth curvature has negligible error in mid-range guidance weapon system's scope.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.27-31
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• 2003

Underwater acoustic navigation systems are classified into three systems: ultra-short baseline (USBL), short baseline (SBL), and long baseline (LBL). Because the USBL system estimates the angle of a submersible, the estimation error becomes large if the submersible is far from the USBL transducer array mounted under a support vessel. SBL and LBL systems estimate submersible's location more accurately because they have wider distribution of measuring sensors. Especially LBL systems are widely used as a navigation system for deep ocean applications. Although it is most accurate system it still has estimation errors because of noise, measurement error, refraction and multi-path of acoustic signal, or wrong information of the distributed transponders. In this paper the estimation error of the LBL system are analyzed from a point of sensitivity. It is assumed that the error exists only in the distance between a submersible and the transponders. For this purpose sensitivity of the estimated position with respect to relative distances between them is analyzed. The result says that estimation error is small if the submersible is close to transponders but not near the ocean bottom.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.1009-1011
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• 2002

We developed a Retinal Projection Display for a low vision aid. This device can be applied to a low vision whose visual sense is weak. In the device, a digital image was formed with spatial light modulator(SLM) and projected onto a retina with the Maxwellian View. The image on this display can be seen clearly without our ocular accommodation and a low vision can see it without correction of a refraction error.

• Journal of Korean Ophthalmic Optics Society
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• v.21 no.2
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• pp.119-126
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• 2016

Purpose: To analyze the effect of accommodative control and change values between subjective refraction (SR) and auto-refraction (AR) according to application of fogging after accommodative stimulation depending on ametropia type. Methods: Myopic ametropia 76 eyes and hyperopic ametropia 52 eyes participated for this study. SR and AR values measured by three test conditions (Before accommodative stimulation; Before AS, After accommodative stimulation; After AS, and After application of fogging; After AF) were compared, respectively. Results: In myopic eyes, (-)spherical power by SR and AR in After AS test was significantly increased as compared to Before AS test, (-)spherical power in After AF test was decreased to the level of Before AS test. The differences of spherical power between SR and AR were highly measured by SR in After AS test, and highly measured by AR in After AF test, respectively. In hyperopic eyes, (+)spherical power of SR significantly decreased in After AS test compared to Before AS test, more (+)spherical power was detected in After AF test compared to Before AS test. (+)spherical power of AR have no significant difference between Before AS and After AS test, but more (+)spherical power was detected in After AF test compared to Before AS test. The differences of (+)spherical power between SR and AR were significant in all test conditions. Among 52 eyes which were measured as hyperopic ametropia, 7 eyes were measured as myopia by SR in After AS test. In case of AR, 25 eyes among 52 eyes were mismeasured as myopia of ranges from -0.25 D to -1.25 D in Before AS test, 26 eyes in After AS test, and 19 eyes in After AF test were mismeasured as myopia of ranges from -0.25 D to -1.25 D. Conclusions: Regardless of ametropia type, accommodative control by After AF test was effective on both refraction process. However, in auto-refraction for hyperopic eyes, the misdetermined proportion of refractive error's type was high due to consistent accommodative intervention in all test condition. Therefore, in order to obtain an accurate value of refractive errors, full correction should be determined by subjective refraction process after fogging method.

• Journal of Korean Ophthalmic Optics Society
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• v.4 no.1
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• pp.7-14
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• 1999

The purpose of this study is to evaluate the relationship between ocular components and refractive error for human eye. Ocular components were measured by keratometry, phakometry, and ultrasonography. Refractive error was measured by subjective refraction on 38 subjects aged from 17 to 30. The results were as follows; 1) Refractive error and axial length, vitreous chamber depth, axial length/corneal radius were highly correlated that the correlation coefficients were 0.95, 0.96, 0.95, respectively. 2) Refractive error and corneal radius, corneal power, lens thickness were correlated with the correlation coefficients for 0.60, 0.66, 0.67 respectively. 3) There were no significant correlation between refractive error and corneal thickness.

• Journal of Korean Ophthalmic Optics Society
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• v.16 no.4
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• pp.425-431
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• 2011

Purpose: For better understanding refractive error in Korean children and teenagers, a follow-up study on the changes of refractive error was performed in 1~13-year-old subjects for ten years. Methods: Among the people who had visited an ophthalmologic hospital in Seoul to examine the visual acuity and to correct refractive error from 2000 to 2010 years, 223 subjects (364 eyes) having the corrected visual acuity over 0.7 had been investigated the changes of spherical equivalent power of the cycloplegic clinical refraction and manifest clinical refraction from the accumulated medical record data for ten years. Results: The changes of spherical equivalent power for ten years in 1 to 13 years old were shown the highest change at 7-year-old. And annual change of spherical equivalent power was shown the highest change at from 9-year-old to 10-year-old (-0.64${\pm}$0.64 D) followed by from 8-year-old to 9-year-old (-0.64${\pm}$0.81 D). Conclusions: The changes of refractive error for Korean children and teenagers aged 1 to 13 years in an optometric practice were shown the tendency to proceeding to myopia with age, especially the largest increase at from 7-year-old to 10-year-old, and this period is important for vision care.