• Journal of the Korean Geosynthetics Society
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• v.13 no.3
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• pp.1-10
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• 2014

Several types of methods such as resistivity survey, ground penetration radar, etc are used for detection of levee leakage and according to the river design guidelines detection of levee leakage is performed by measuring the hydraulic conductivity of levee soil. But, the former can not verify the leakage point and degree of saturation, the latter is an after treatment method. Movable sensor, which is a high-tech TDR system developed since 2000, can obtain directly the dielectric constant profile covering the whole depth of levee. In this study, laboratory and field model experiments were carried out using movable TDR sensor in order to evaluate the applicability as detection system of levee leakage, As the result, movable TDR system has proven to be 3 times more sensitive to water contents than dry unit weight, and the results conclude that the dielectric constant, water contents and density of the ground proved to have a correlation among them, and the dielectric constant is expected to be a basic data on detection of levee leakage.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1998.10a
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• pp.407-413
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• 1998

Considerable progress has been made in the application of time-domain reflectrometry(TDR) to measurement of soil water content. The TDR provides a means of monitoring the water content of soil over a wide range of values, in the field and in the laboratory The TDR measures the volumetric moisture content of the soil via a bureid sensor(probe). Probes can be buried and monitored remotely and an immediate result can be obtained. In addition to, the results are very reliable.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.329-336
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• 2013

The infrastructure of flexible pavement is composed of aggregate subbase, anti-frost layer, and subgrade. In particular, the subgrade performance is affected by climates such as frost action and precipitation. The method of TDR(Time Domain Reflectometry) sensors to measure moisture contents in subgrade layer has been used in the research. Due to the TDR method using dielectric permitivity of soil and water, the sensors can be affected by the low subgrade temperatures. The air temperatures frequently drops below $-20^{\circ}C$ in the winter in Korea. As a result, it is necessary to estimate the accuracy of the TDR moisture sensors in the range of below zero temperatures. In this study, the subgrade temperatures of lower than $-2^{\circ}C$ were extended to evaluate temperature sensitivity of the TDR moisture sensors. The test results revealed that the moisture contents around the sensors were reduced while those of the upper part of specimen showed a tendency to increase as the specimen surface temperature drops below zero under the volumetric moisture contents(VMC) of 20% and 30%. However, the impact of temperature on the function of the sensor at lower water contents was found to be negligible if any.

• Journal of the Korean Geotechnical Society
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• v.27 no.2
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• pp.63-72
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• 2011

The measured ground water behavior by TDR (time domain reflectometer) sensors were analyzed by the data filtering technique such as moving average method and Fourier transform, and the ground water level and unsaturated zone were tried to be determined numerically. At first, the variation of TDR data according to the saturation degree was measured by lab test, which is translated as a function of saturation degree. Then, changes of ground water level and lateral seepage in field conditions were simulated using acrylic pipe, and the measured data were analyzed to make calibration curve. Furthermore, TDR sensors were installed into the in-situ embankment to insure the field application. The saturation degree, unsaturated and dried zones were determined from the measured data.

• Journal of Sensor Science and Technology
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• v.30 no.6
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• pp.415-419
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• 2021

We developed a highly accurate, yet inexpensive, refractive index (RI)-based soil moisture sensor. To detect the RI, a light guide was set with a light-emitting diode and photodiode. When the air fills the space between the soil particles, most of the incident light is reflected at the interface between the waveguide and the air because of the large RI difference. As the moisture of the soil increases, the macroscopic soil RI increases. This allows incident light to pass through the interface. The intensity of the light reaching the photodiode was simulated according to the change in the soil RI. Using the simulation results, we designed and manufactured a curved glass waveguide. We evaluated the performance of the RI-based soil sensor by comparing it with a commercially available, high-cost and high-performance time-domain reflectometer (TDR). Our sensor was 96% accurate, surpassing the costly TDR sensor.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.5
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• pp.89-99
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• 2019

In this study, we estimated the spatially-distributed soil moisture at the high resolution ($10m{\times}10m$) using the satellite-based Sentinel-1A/B SAR (Synthetic Aperture Radar) sensor images. The Sentinel-1A/B raw data were pre-processed using the SNAP (Sentinel Application Platform) tool provided from ESA (European Space Agency), and then the pre-processed data were converted to the backscatter coefficients. The regression equations were derived based on the relationships between the TDR (Time Domain Reflectometry)-based soil moisture measurements and the converted backscatter coefficients. The TDR measurements from the 51 RDA (Rural Development Administration) monitoring sites were used to derive the regression equations. Then, the soil moisture values were estimated using the derived regression equations with the input data of Sentinel-1A/B based backscatter coefficients. Overall, the soil moisture estimates showed the linear trends compared to the TDR measurements with the high Pearson's correlations (more than 0.7). The Sentinel-1A/B based soil moisture values matched well with the TDR measurements with various land surface conditions (bare soil, crop, forest, and urban), especially for bare soil (R: 0.885~0.910 and RMSE: 3.162~4.609). However, the Mandae-ri (forest) and Taean-eup (urban) sites showed the negative correlations with the TDR measurements. These uncertainties might be due to limitations of soil surface penetration depths of SAR sensors and complicated land surface conditions (artificial constructions near the TDR site) at urban regions. These results may infer that qualities of Sentinel-1A/B based soil moisture products are dependent on land surface conditions. Although uncertainties exist, the Sentinel-1A/B based high-resolution soil moisture products could be useful in various areas (hydrology, agriculture, drought, flood, wild fire, etc.).

• 한국방재학회:학술대회논문집
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• 2010.02a
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• pp.89.1-89.1
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• 2010

본 연구는 토양의 함수비를 측정하기 위하여 TDR(Time Domain Reflectometry, 시간영역 광전자파 분석기) 방식의 함수센서(CS616)에 대한 올바른 보정시험을 제안하기 위하여 피복두께, 센서간 간섭 영향, 온도의 영향 및 다짐율 변화에 대한 실내 시험을 수행하였다. 시험 결과 피복두께, 센서간 간섭 영향 및 온도의 영향은 체적함수비의 크기에 미치는 영향은 크지 않은 것으로 나타났으며, 오히려 보정시험시 정확한 체적함수비 조건을 유지하는 것이 중요할 것으로 사료된다. 또한 보정시험을 수행할 때 다짐율까지 고려한 시험을 수행하는 노력에 비하여 얻어지는 체적함수비의 정확도의 크기는 다짐율과 주기를 고려하여 얻어진 회귀식을 살펴보면 주기에 비하여 상대적으로 영향이 작은 것으로 사료된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.76-76
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• 2015

토양수분은 생태수문학에서 식생과의 상호작용의 중요한 인자이자, 대기와의 상호작용으로 인한 총체적인 물 순환에 밀접한 관련이 있다. 수문학적으로는 증발, 침투, 지하수 함량, 토양 침식, 식생 분포 등을 지배하는 중요한 요소이고, 특히 시 공간적 분포특성은 강수 사상 후 토양으로의 침투 및 토양수분의 재분포, 증발산과 불포화대에서의 오염물의 이송을 예측하는데 매우 중요하다. 또한, '07년 하천법 개정으로 증발산량 및 토양수분량이 신규 수문조사 항목으로 추가되어, 토양수분 측정에 대한 필요성이 높아졌다. 따라서, 2008년 5월, K-water연구원에서는 현재 시험유역으로 운영하고 있는 용담시험유역에 토양수분관측망(6개 관측소)을 구축하였다. 토양수분계는 토양수분을 결정하는 가장 중요한 인자인 강우자료의 획득이 이루어지는 지점에 설치하여 정확도와 신뢰도를 높일 수 있도록 용담시험 유역 내 6개 우량관측소에 설치하였다. 하지만 장비의 노후화에 따른 자료 취득의 어려움으로 인하여 2013년 4월, 토양수분계를 전면 교체하였다. 토양수분계는 기존의 FDR 방식에서 EC 농도에 대한 영향이 가장 적고, 플럭스 타워에 위치한 토양수분계 센서와 동일한 TDR 방식의 센서로 장비를 전면 교체하였다. 센서 설치 장소 변경에 따른 TDR 센서의 검증과 그리고 흙의 종류, 입도, 다짐도, 온도 등에 의한 오차가 발생 여부를 판단하기 위하여 이에 대한 보정을 실시하였다. 원지반 시료채취를 통하여 토양수분량을 측정하였고, TDR 센서에 의해 측정된 토양수분량과 채취된 시료에서 측정된 토양수분량의 결과를 비교하였고, 각 지점별 토양구성비와 전기전도도 조건을 고려하여 각 토층별 계수적용을 달리하여 센서 보정을 실시하였다. 그 결과 기존 센서 제조사에서 제안한 방정식을 그대로 사용하는 것 보다는 센서 검증을 통하여 얻은 계수보정에 의한 토양수분 변환식을 사용하는 것이 정확한 현장 자료를 확보할 수 있고, 신뢰도 높은 자료를 얻을 수 있다고 판단된다.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.2
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• pp.23-30
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• 2010

The research presents moisture content measuring and calibration method of road pavement, especially asphalt concrete pavement for performance evaluation or remaining life prediction using Time Domain Reflectometry(TDR) sensor, CS616 made by campbell INC. Before calibration test of CS616, accomplished a sensor verification tests. Verification test items were covering depth and interference effect of two CS616 sensors, temperature effects between $5^{\circ}C\sim25^{\circ}C$ and compaction ratio effects. Covering depth and interference effects between two CS616 sensors were just small and the effects of temperature and compaction ratio effected a Volumetric Moisture Contents at $\pm6%$ under disregard appeared with the fact that was possible. Also, obtained the calibration equation of the subgrade and subbase course, $R^2$ showed above of all 0.9.

• Korean Journal of Soil Science and Fertilizer
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• v.42 no.2
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• pp.110-116
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• 2009

This study was to verify and calibrate seven kinds of soil water sensors for volumetric soil water content(VSWC) measurement under field. Types of sensors were TDR (Time Domain Reflectometry) and FDR(Frequency Domain Reflectometry). Two kinds of TDR were TRIME(profile type), and Mini-TRASE(rod type). Five kinds of FDR were EasyAG, EnviroSCAN, PR-1(profile type), and WET-1(rod type). VSWC by TRIME and Mini-TRASE compared with VSWC by soil core showed the standard error of about 2.4%, and 1.4% which is the smallest value among all the sensors used in the experiment, respectively. The errors of EasyAG and EnviroSCAN analyzed with scaled frequency(SF) were about 2.6%, and 2.8% and those by 1 versus 1 correspondence were about 2.6%, and 2.6%, respectively. WET-1 showed about 2.0% of error, which is the smallest value among errors by FDR sensors. PR-1 with the error of about 4.7% should be hard for application in field. Therefore, users on soil water sensors have to take into consideration the errors of sensors revealed after the calibration for the correct measurement of VSWC in field. The rest except for PR-1 among the sensors could be used for VSWC measurement with 1.4~2.6% error.