• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.2 s.54
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• pp.181-188
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• 2009

Measuring the tensile strength of steel cables used to support bridges is a critical inspection item in terms of the safety of a bridge. Today, cable tension is measured with the vibration method and loadcell. Recently, some advanced countries have conducted studies on measuring tension with magnetic method and are suggesting prospective results. Since there were no such studies ongoing in Korea, we began a study on measuring tension with magnetic method as we are undergoing researches to improve the precision of measurements. It is necessary to consider the influence for the magnetic field and the temperature of steel cables in tension measurement of magnetic method. In this paper, we tested an output characteristic of tension sensor according to temperature and deduced temperature compensation coefficient in the given magnetic field and applied the compensation coefficient to the tension measurement system in the lab. We analyzed and evaluated testing results for the output voltages of the tension sensor according to cable tensions.

• Korean Journal of Remote Sensing
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• v.39 no.6_1
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• pp.1273-1281
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• 2023

Absolute radiometric calibration is a crucial process in converting the electromagnetic signals obtained from satellite sensors into physical quantities. It is performed to enhance the accuracy of satellite data, facilitate comparison and integration with other satellite datasets, and address changes in sensor characteristics over time or due to environmental conditions. In this study, field campaigns were conducted to perform vicarious calibration for the multispectral channels of the CAS500-1. Two valid field observations were obtained under clear-sky conditions, and the top-of-atmosphere (TOA) radiance was simulated using the MODerate resolution atmospheric TRANsmission 6 (MODTRAN 6) radiative transfer model. While a linear relationship was observed between the simulated TOA radiance of tarps and CAS500-1 digital numbers(DN), challenges such as a wide field of view and saturation in CAS500-1 imagery suggest the need for future refinement of the calibration coefficients. Nevertheless, this study represents the first attempt at absolute radiometric calibration for CAS500-1. Despite the challenges, it provides valuable insights for future research aiming to determine reliable coefficients for enhanced accuracy in CAS500-1's absolute radiometric calibration.

• Korean Journal of Remote Sensing
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• v.24 no.2
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• pp.213-222
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• 2008

Although hyperspectral sensing data have shown great potential to derive various surface information that is not usually available from conventional multispectral image, the acquisition of proper hyperspectral image data are often limited. To use ground-based hyperspectral camera image for remote sensing studies, radiometric calibration should be prerequisite. The objective of this study is to develop radiometric calibration procedure to convert image digital number (DN) value to surface reflectance for the 120 bands ground-based hyperspectral camera. Hyperspectral image and spectral measurements were simultaneously obtained from the experimental target that includes 22 different surface materials of diverse spectral characteristics at wavelength range between 400 to 900 nm. Calibration coefficients to convert image DN value to at-sensor radiance were initially derived from the regression equations between the sample image and spectral measurements using ASD spectroradiometer. Assuming that there is no atmospheric effects when the image acquisition and spectral measurements were made at very close distance in ground, we were also able to derive calibration coefficients that directly transform DN value to surface reflectance. However, these coefficients for deriving reflectance values should not be applied when the camera is used for aerial image that contains significant effect from atmosphere and further atmospheric correction procedure is required in such case.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.28-28
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• 2022

본 연구는 용담댐유역을 포함한 금강 유역 상류 지역을 대상으로 Sentinel-1 SAR (Synthetic Aperture Radar) 위성영상을 기반으로 한 토양수분 산정을 목적으로 하였다. Sentinel-1 영상은 2019년에 대해 12일 간격으로 수집하였고, 영상의 전처리는 SNAP (SentiNel Application Platform)을 활용하여 기하 보정, 방사 보정 및 Speckle 보정을 수행하여 VH (Vertical transmit-Horizontal receive) 및 VV (Vertical transmit-Vertical receive) 편파 후방산란계수로 변환하였다. 토양수분 산정에는 Water Cloud Model (WCM)이 활용되었으며, 모형의 식생 서술자(Vegetation descriptor)는 RVI (Radar Vegetation Index)와 NDVI (Normalized Difference Vegetation Index)를 활용하였다. RVI는 Sentinel-1 영상의 VH 및 VV 편파자료를 이용해 산정하였으며, NDVI는 동기간에 대해 10일 간격으로 수집된 Sentinel-2 MSI (MultiSpectral Instrument) 위성영상을 활용하여 산정하였다. WCM의 검정 및 보정은 한국수자원공사에서 제공하는 10 cm 깊이의 TDR (Time Domain Reflectometry) 센서에서 실측된 6개 지점의 토양수분 자료를 수집하여 수행하였으며, 매개변수의 최적화는 비선형 최소제곱(Non-linear least square) 및 PSO (Particle Swarm Optimization) 알고리즘을 활용하였다. WCM을 통해 산정된 토양수분은 피어슨 상관계수(Pearson's correlation coefficient)와 평균제곱근오차(Root mean square error)를 활용하여 검증을 수행할 예정이다.

• Journal of Bio-Environment Control
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• v.31 no.4
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• pp.401-408
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• 2022

As research on a controlled environment system based on crop growth environment sensing for sustainable production of horticultural crops and its industrial use has been important, research on how to properly utilize soil moisture sensors for outdoor cultivation is being actively conducted. This experiment was conducted to suggest the proper method of utilizing the TEROS 12, an FDR (frequency domain reflectometry) sensor, which is frequently used in industry and research fields, for each orchard soil in three regions in Korea. We collected soils from each orchard where fruit trees were grown, investigated the soil characteristics and soil water retention curve, and compared TEROS 12 sensor calibration equations to correlate the sensor output to the corresponding soil volumetric water content through linear and cubic regressions for each soil sample. The estimated value from the calibration equation provided by the manufacturer was also compared. The soil collected from all three orchards showed different soil characteristics and volumetric water content values by each soil water retention level across the soil samples. In addition, the cubic calibration equation for TEROS 12 sensor showed the highest coefficient of determination higher than 0.95, and the lowest RMSE for all soil samples. When estimating volumetric water contents from TEROS 12 sensor output using the calibration equation provided by the manufacturer, their calculated volumetric water contents were lower than the actual volumetric water contents, with the difference up to 0.09-0.17 m³·m^-3 depending on the soil samples, indicating an appropriate calibration for each soil should be preceded before FDR sensor utilization. Also, there was a difference in the range of soil volumetric water content corresponding to the soil water retention levels across the soil samples, suggesting that the soil water retention information should be required to properly interpret the volumetric water content value of the soil. Moreover, soil with a high content of sand had a relatively narrow range of volumetric water contents for irrigation, thus reducing the accuracy of an FDR sensor measurement. In conclusion, analyzing soil water retention characteristics of the target soil and the soil-specific calibration would be necessary to properly quantify the soil water status and determine their adequate irrigation point using an FDR sensor.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
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• 2004.03a
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• pp.247-250
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• 2004

OSMI/KOMPSAT-I 위성의 Level-0 영상자료의 줄무늬 제거에 대한 연구가 수행되었다. 이 줄무늬 원인은 크게 2가지로 구분되었다. 하나는 96 pixel CCD의 전반부와 후반부에 따라 얻어지는 신호크기 차이 있으며, 다른 하나는 pixel간의 감도의 차이가 있는 것으로 나타났다. 문제는 각 영상자료마다 이들의 보정계수가 일치하지 못하여 매 영상으로부터 새로운 보정계수가 필요하다는 것이다. 줄무늬 제거의 근본적인 접근은 바로 2가지 문제를 해결하는 방향으로 접근하였다. 즉, 첫 번째 문제인 전후반부의 CCD pixel에서 얻어지는 신호의 크기 차이가 감도의 차이인지 아니면 upset 값의 차이인지가 규명되었고, 동시에 각 센서 pixel의 감도 역시 신호의 세기에 따라 감도가 다른 것으로 나타났다. 본 연구에서는 이러한 모든 줄무늬 보정 정보를 매 영상마다 독립적으로 얻게 하여 OSMI 위성영상의 질을 보다 높일 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.11
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• pp.1133-1137
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• 2011

A novel technique for the fabrication of a glass micropipette-based thermal sensor was developed utilizing inexpensive thermocouple materials. Thermal fluctuation with a resolution of ${\pm}0.002$ K was measured using the fabricated thermal probe. The sensors comprise unleaded low-melting point solder alloy (Sn) as a core metal inside a borosilicate glass pipette coated with a thin film of Ni, creating a thermocouple junction at the tip. The sensor was calibrated using a thermally insulated calibration chamber, the temperature of which can be controlled with a precision of ${\pm}0.1$ K and the thermoelectric power (Seebeck coefficient) of the sensor was recorded from 8.46 to $8.86{\mu}V$/K. The sensor we have produced is both cost-effective and reliable for thermal conductivity measurements of micro-electromechanical systems (MEMS) and biological temperature sensing at the micron level.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2017.11a
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• pp.88-90
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• 2017

현재 한국해양과학기술원에서는 선박비행체 탑재용 복합센서를 개발 및 시험 적용 중에 있다. 그러나 얻어진 영상 데이터를 통해서는 목표물에 대한 정확한 위치 정보를 파악할 수 없다. 또한 크기가 큰 물체도 거리가 멀면 영상에선 작아 보이기 때문에 목표물의 크기 또한 파악하기 힘들다. 이를 보완하기 위해 본 연구에서는 복합센서를 통해 획득한 영상에 대해 warping 및 기하보정, 선박 및 익수자 자동 탐지 알고리듬, 위치 및 계수 정보 산출에 대해 소개한다. 또한 실제 실험을 통해 해당 알고리듬을 검증하였다.

• The Journal of the Korea Contents Association
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• v.21 no.1
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• pp.277-283
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• 2021

Traffic data by vehicle classification are important data used as basic data in various fields such as road and traffic design. Traffic data is collected through permanent and temporary surveys and is provided as an annual average daily traffic (AATD) in the statistical yearbook of road traffic. permanent surveys are collected through traffic collection equipment (AVC), and the AVC consists of a loop sensor that detects traffic volume and a piezo sensor that detects the number of axes. Due to the nature of the buried type of traffic collection equipment, missing data is generated due to failure of detection equipment. In the existing method, it is corrected through historical data and the trend of traffic around the point. However, this method has a disadvantage in that it does not reflect temporal and spatial characteristics and that the existing data used for correction may also be a correction value. In this study, we proposed a method to correct the missing traffic volume by calculating the axis correction coefficient through the accumulated number of axes acquired by using a piezo sensor that can detect the axis of the vehicle. This has the advantage of being able to reflect temporal and spatial characteristics, which are the limitations of the existing methods, and as a result of comparative evaluation, the error rate was derived lower than that of the existing methods. The traffic volume correction system using axis count is judged as a correction method applicable to the field system with a simple algorithm.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.127-127
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• 2011

본 연구에서는 RHESSys (Regional Hydro-Ecologic Simulation System) 모형을 이용하여 산림 유역의 생태수문학적 거동을 평가하고자 한다. 설마천 유역($8.48\;km^2$)을 대상으로 2007~2009년의 관측 일유출량을 이용하여 유출량을 검 보정하였고, 증발산량 및 토양수분은 신뢰할 만한 실측자료를 바탕으로 모형의 보정(2007-2008)및 검증(2009)을 실시하였다. 또한 지구의 탄소순환을 규명할 수 있는 식생의 순광합성량과 총일차생산량에 대한 모형의 검 보정은 Terra 위성의 MODIS (Moderate Resolution Imaging Spectroradiometer) 센서를 이용한 산출물인 순광합성량과 총일차생산량 자료를 바탕으로 모형의 보정(2007)및 검증(2008)을 실시하였다. 모형의 최적의 수문, 생리생태학, 토양의 매개변수를 선정하여 검증한 결과, 유출량에 대한 Nash-Sutcliffe 모형효율은 0.84, 증발산, 토양수분, 총일차생산량, 순광합성량의 결정계수는 0.49, 0.18, 0.38, 0.93 이었다.