• Journal of Korean Society for Geospatial Information Science
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• v.18 no.1
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• pp.89-97
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• 2010

The ship-borne gravity data is essential to construct geoid in Korea surrounding ocean area. The altimeter data was used in previous study, however, the ship-borne gravity data could be used due to more ship-borne data was collected by improvement of instrument, positioning system. Therefore, the study on verification of precision of ship-borne gravity data and practical usage analysis is needed. In this study, free-air anomaly having 16.47mGal and 18.86mGal as mean and standard deviation was obtained after consistent processing such as Eotvos correction, Kalman Filter, Cross-over adjustment etc. The calculated free-air anomaly was compared to DNSC08 altimeter data and the difference was computed having -0.88mGal and 9.46mGal of mean and standard deviation. The reason causing those differences are owing to spatial limits of data acquisition and effects of ocean topography. To use ship-borne gravity data for precision geoid development, the efforts to overcome the limits of data collection and study for data combination should be proceeded.

• Geophysics and Geophysical Exploration
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• v.20 no.3
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• pp.163-175
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• 2017

In land seismic exploration, irregular surface topography and weathering layer in near surface distorts the reflected signals of data. Therefore, typical land seismic data should be compensated for this distortion by static correction. To perform the static correction, near-surface velocity is required, which can be obtained by seismic refraction survey. However, land seismic data is often acquired in a limited form of geometry depending on the equipment availability, accessibility condition, and permission for the survey site. In this situation, refraction analysis should be performed using reflection data because it is impossible to acquire refraction-oriented data due to limited source and receiver geometry. In this study, we aimed to analyze the reliability of the results obtained by refraction traveltime tomography when using reflection data with a limited number of sources and receivers from irregular surface topography. By comparing the inversion result from irregular topography with that from flat surface, we found that the surface topography affects the reliability of the inversion results to some degree. We also found that the number of sources has little effect on the inversion results unless the number of sources are very small. On the other hand, we observed that velocity distortion occurred in the overlapped part of receiver arrays when using a limited number of receivers, and therefore suggested the size of the least overlapping ratio to avoid the velocity distortion. Finally, we performed numerical tests for the model which simulates the surface topography and acquisition geometry of the survey region and verified the reliability analysis of inversion results. We identified reliable areas and suspicious area of the inverted velocity model by applying the analysis results to field data.

• Korean Journal of Agricultural and Forest Meteorology
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• v.25 no.4
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• pp.368-375
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• 2023

In this study, we examined the error characteristic and bias correction method for one-month temperature forecast data produced through joint development between the Rural Development Administration and the H ong Kong University of Science and Technology. For this purpose, hindcast data from 2013 to 2021, weather observation data, and various environmental information were collected and error characteristics under various environmental conditions were analyzed. In the case of maximum and minimum temperatures, the higher the elevation and latitude, the larger the forecast error. On average, the RMSE of the forecast data corrected by the linear regression model and the XGBoost decreased by 0.203, 0.438 (maximum temperature) and 0.069, 0.390 (minimum temperature), respectively, compared to the uncorrected forecast data. Overall, XGBoost showed better error improvement than the linear regression model. Through this study, it was found that errors in prediction data are affected by topographical conditions, and that machine learning methods such as XGBoost can effectively improve errors by considering various environmental factors.

• Korean Journal of Remote Sensing
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• v.28 no.4
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• pp.393-407
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• 2012

This study focuses on the correction of topographic effects caused by a combination of solar elevation and azimuth, and topographic relief in single optical remote sensing imagery, and by a combination of changes in position of the sun and topographic relief in comparative analysis of multi-temporal imageries. For the Jeju Island, Republic of Korea, where Mt. Halla and various cinder cones are located, a Landsat 7 ETM+ imagery and ASTER GDEM data were used to normalize the topographic effects on the imagery, using two topographic normalization methods: cosine correction assuming a Lambertian condition and assuming a non-Lambertian c-correction, with kernel sizes of $3{\times}3$, $5{\times}5$, $7{\times}7$, and $9{\times}9$ pixels. The effects of each correction method and kernel size were then evaluated. The c-correction with a kernel size of $7{\times}7$ produced the best result in the case of a land area with various land-cover types. For a land-cover type of forest extracted from an unsupervised classification result using the ISODATA method, the c-correction with a kernel size of $9{\times}9$ produced the best result, and this topographic normalization for a single land cover type yielded better compensation for topographic effects than in the case of an area with various land-cover types. In applying the relative radiometric normalization to topographically normalized three multi-temporal imageries, more invariant spectral reflectance was obtained for infrared bands and the spectral reflectance patterns were preserved in visible bands, compared with un-normalized imageries. The results show that c-correction considering the remaining reflectance energy from adjacent topography or imperfect atmospheric correction yielded superior normalization results than cosine correction. The normalization results were also improved by increasing the kernel size to compensate for vertical and horizontal errors, and for displacement between satellite imagery and ASTER GDEM.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.5
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• pp.417-428
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• 2017

In this paper, we describe the architectural design, unit component hardware design and core software design(Helmet Pose Tracking Software and Terrain Elevation Data Correction Software) of IHDS(Intelligent Helmet Display System), and describe the results of unit test and integration test. According to the trend of the latest helmet display system, the specifications which includes 3D map display, FLIR(Forward Looking Infra-Red) display, hybrid helmet pose tracking, visor reflection type of binocular optical system, NVC(Night Vision Camera) display, lightweight composite helmet shell were applied to the design. Especially, we proposed unique design concepts such as the automatic correction of altitude error of 3D map data, high precision image registration, multi-color lighting optical system, transmissive image emitting surface using diffraction optical element, tracking camera minimizing latency time of helmet pose estimation and air pockets for helmet fixation on head. After completing the prototype of all system components, unit tests and system integration tests were performed to verify the functions and performance.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.7
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• pp.629-639
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• 2016

Batch process TRN(Terrain Relative Navigation) using an altimeter is a technique to correct position by correlating a series of periodically measured terrain height profile and terrain height candidate profile of the DEM(Digital Elevation Map). However, it is generally known that the performance of TRN is degraded when measured terrain height profile and terrain height candidate profiles of the DEM are similar at hill or repetitive terrain. In this paper, area based terrain slope roughness index[11] is applied and area based terrain curvature roughness index which can detect similarity of terrain in ROI(Region Of Interest) is proposed to overcome this problem. Applying terrain roughness indexes to terrain relative navigation system of lunar lander, it is shown that TRN using area based terrain roughness results in improved performance compared to conventional trajectory based method through simulation.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.12 no.1
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• pp.107-118
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• 1994

As satellite altimetry is being progressed to apply with heigher precision to maginal seas, it was necessary to improve correction procedures for tidal signals in altimetry with more accurate tidal model than well-known model of Schwiderski for studying marginal sea dynamics. As a first step, tidal regime of semidiurnal tides$(M_2,\;S_2,\;N_2,\;K_2)$ and diurnal tides$(K_1,\;O_1,\;P_1,\;Q_1)$ were computed with a finer details of formulation of tidal model over the East Asian Marginal Seas covering the Okhotsk Sea and South China Sea and part of Northwest Pacific Ocean with mesh resolutions of 1/6$^{\circ}$. Subsequently the computed sets of harmonic constants from the model were used to remove the tide in selected Sea Surface Heights from Geosat in the modelled region. Preliminary correction procedure suggested in the present study may be extensively used for obtaining Sea Surface Topography over the East Asian Marginal Seas, especially for the region where Schwiderski's harmonic constants are not available.

• Proceedings of the Korea Contents Association Conference
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• 2007.11a
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• pp.942-946
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• 2007

The new gravity field combination models are expected to improve the knowledge of the Earth's global gravity field. This study evaluates six global gravity field models derived from gravimetry and altimetry surface data in a comparison with ground truth in South Korea. For calculating a more accurate estimate of the geoid heights from the height anomalies, the terrain corrections due to the terrain masses over geoid have considered, the model for the topographic correction is a spherical harmonic expansion of the ETOPO2 DTM model. Geoid heights obtained from GPS and levelling in land area of South Korea are compared with those from the EGMs. The results show that EIGEN-CG03C EGM and EIGEN-GL04C EGM displayed the nearest results to GPS/leveling, and also confirmed the importance of terrain correction for geoid height in case of the uneven topography.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.211.2-211.2
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• 2012

천리안위성은 통신, 해양, 기상 임무를 띤 우리나라 최초의 정지궤도복합위성으로 지난 2010년 6월 27일 성공적으로 발사된 후 동경 128.2도, 적도 상공 약 35,800 km 고도의 정지궤도에 안착되었다. 이 후 약 6개월 여의 궤도상시험 기간과 2개월의 안정화 기간을 거쳐 2011년 4월 1일, 기상청은 위성자료 서비스를 위한 정규운영을 시작하였다. 천리안위성의 기상탑재체인 기상영상기는 다중채널 복사계로 한반도 주변뿐만 아니라 전 지구적 기후 변화 및 대기 운동 그리고 급변하는 기상상황을 감시하기 위해 실시간 관측과 전송 시스템을 갖추고 있다. 이 기상영상기를 운용하는 기상청 국가기상위성센터 지상국에서는 자료수신 및 영상전처리시스템을 갖추고 수신된 위성신호로부터 영상 분리 후 복사보정 및 기하보정을 수행하며, 위성자료배포시스템을 통해 일정 시간 간격 내에 사용자들에게 처리 자료를 배포하고 있다. 영상 복사보정은 기상영상기 내의 각 채널별 디텍터가 감지한 지구복사휘도의 전기적 신호를 지상에서 복사휘도와 휘도온도 값으로 변환하는 작업이다. 절대검정체로서 흑체와 우주보기 값을 이용하는 적외채널과 달리, 가시채널 디텍터는 절대검정체가 탑재되어있지 않기 때문에 우주보기 값 외에 대리검정 방법을 이용한다. 이러한 가시채널 노화도 분석에 달 관측을 통한 비교 분석이 한 방법으로 제시되고 있다. 천리안위성 기상영상기의 정규운영 1년간의 가시채널 디텍터의 노화도는 6 % 이내로 측정되었고, 이는 일반적인 정지궤도위성 센서의 노화도인 6 % 내외 값 변화량에 견주어 잘 운용되고 있음을 시사한다. 본 논문에는 천리안위성 기상영상자료의 품질 및 매개변수의 변화 경향도 함께 제시하였으며, 달을 이용한 기상영상기 노화 분석과 보정에 관한 내용을 싣고 있다.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.155-155
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• 2012

최근 집중호우에 따른 자연재해가 크게 증가하여 수문 및 기상분야에서 강우를 관측 및 예측하기 위한 레이더 활용성이 증대되고 있으며, 이에 따라 정부 각 관련부처에서는 레이더의 도입 및 확충을 위한 방안을 계획 제시하고 있다. 특히, 레이더강우 자료는 수문해석분야에서의 GIS 등 디지털정보를 이용하여 유역매개변수를 추정함에 따라 더 정확하고 상세한 수문자료 확보가 가능하게 되어, 격자기반의 분포형 강우-유출모형 등을 이용하여 수문해석을 하는데 있어 그 활용성이 크게 증가하고 있다. 그러나 레이더강우 자료의 정확성은 아직까지 만족할 만한 수준에 이르지 못하고 있기 때문에, 그 불확실성으로 인하여 레이더강우 자료의 활용 및 적용에 한계를 가지고 있는 실정이다. 본 연구에서는 지상강우를 이용한 레이더강우 보정을 위하여 SOA(Statistical Objective Analysis)보정방법을 이용하였으며, 기존 SOA방법에서의 거리에 따른 가중치($_{kd}$)와 함께 지형(고도)에 따른 가중치($W_{ike}$), 바람의 영향에 따른 가중치($W_{ikw}$)를 추가로 산정하여 적용하였으며, 이를 통하여 보정된 강우장을 생성하였다. SOA방법을 통해 생성된 강우장이 어느 정도의 강우정확도를 가지고 강우분포를 재현하는지 검증하기 위하여 2011년 7~9월의 수문학적 분석에 활용 가능한 강우사상과 낙동강유역을 대상으로, 분포형모형인 $Vflo^{TM}$ 모형을 이용하여 산정된 유출량과 관측 유출량과의 비교를 실시하였다. 또한, 유출량에 대한 오차 및 ME(Model Efficiency)를 통해 레이더강우 자료의 유출모형에서의 효율성을 검토하고자 하였다. 본 연구에서 수행된 보정 강우장에 따른 유출량 비교를 통해 레이더 강우의 정확도에 대한 정량적 평가 방법 도출이 가능할 것으로 판단된다.