• 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 Bio-Environment Control
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• v.18 no.3
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• pp.238-243
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• 2009

To investigate the characteristics of moisture content (MC), moisture distribution and starting point of drainage in a rockwool slab culture, time domain reflectometry (TDR) sensors were used in a drip irrigation system. MC values ($0{\sim}100%$) measured by TDR sensors in a slab were compared to those by loadcells. Seventy two seedlings of paprika (Capsicum annuum L.) were cultured for $5{\sim}6$ months in a green-house and the starting point of irrigation was determined by the average value of three TDR sensors which were inserted diagonally across the slabs under the plants. MCs as a standard for starting point of irrigation by TDR were determined with 40%, 50%, and 60%. Distribution of MCs in a slab measured with five TDR sensors equally spaced from two irrigation points were not much different when the MC in the slab increased from zero to saturation point. The saturated MCs in the slab were presented at $58{\sim}65%$ and the drain was started when the MC became around $50{\sim}55%$. At the saturated MC in the slab, TDR sensors presented 100% but the values from the loadcell showed 90% at the same time. However, measurement errors between two methods for MC remarkably decreased with a decrease in the MC in a slab. Especially when the MC was maintaining below 60%, the errors between TDR and loadcell methods for measuring MC in the rock-wool slab were less than 5%. There were no significant differences in number of fruits and fresh and dry weights of fruits when they were cultured under the different MC conditions with three irrigation regimes (40%, 50%, and 60%). These results indicated that the MC control by TDR sensors in a rock-wool based paprika culture can be suggested as a method to determine the starting point of irrigation for a soilless culture system.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.79-86
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• 2010

In this paper, using soil slope inclinometer observations of lateral flow is used as a traditional way, but there are some decisions. Inclinometers in the process of installing and monitoring is costly. Severe incline slope of the lateral flow is observed in the inefficient. As a solution for it using TDR sensors are used to. Metal conductors such as coaxial cable and general cable uses a measurement sensor can be installed on site at a lower cost and slope measurements are available for long-term monitoring. When TDR sensor is installed on the slopes, changes in the behavior of slopes causes the earth pressure. TDR sensors determine the change of earth pressure and tried to analyze the behavior of slopes.

• 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.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.404-415
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• 2010

In this paper, using the TDR sensors, variation of soil water content changes were measured as TDR data. Then filtering technique was determined using Fourier transform. Determine the moisture content of soil and ground water level and tried to determine unsaturated zone. First, variation of water content changes were measured TDR data by indoor experiment. Then as a function of TDR data made for water content of soil. Next, through Acrylic indoor laboratory model experiments, changes in ground water levels and lateral penetration of the field conditions were reproduced in an indoor. Field applicability of the TDR sensor was demonstrated by analysis of this. TDR sensor was installed in the embankment, TDR data were measured by TDR sensor.

• Journal of the Korean Geotechnical Society
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• v.30 no.3
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• pp.17-28
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• 2014

In this study, the seepage behavior has been analyzed, which is the most important in determining the stability of the embankment. Large-scale embankment of weathered granite has been installed and TDR (time domain reflectory) sensors were used to detect the seepage lines. The TDR graphs could be separated into 3 sections, which are initial, unsaturated and saturated zones. TDR sensor can detect seepage line more easily than point sensor without analysis. Comparisons of the results of numerical analyses and the TDR sensors showed differences at water level rising condition, and then Comparisons of the results generally showed good agreement at another condition.

• 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.

• Structural Monitoring and Maintenance
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• v.10 no.2
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• pp.133-154
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• 2023

Obscured structural members are mostly under-evaluated during condition assessment due to lack of visual inspection capability. Insufficient information about the integrity of these structural members poses a significant risk for public safety. Time domain reflectometry (TDR) is a novel approach in structural health monitoring (SHM). Ordinary coaxial cables "as is" without a major modification are not suitable for SHM with TDR. The objective of this study is to propose a practical and cost-effective modification approach to commercially available coaxial cables in order to use them as a "cable sensor" for damage detection with the TDR equipment for obscured structural members. The experimental validation and assessment of the proposed modification approach was achieved by conducting 3-point bending tests of the model piles as a representative obscured structural member. It can be noted that the RG59/U-6 and RG6/U-4 cable sensors expose higher strain sensitivity in comparison with non-modified "as is" versions of the cables used. As a result, the cable sensors have the capability of sensing both the presence and the location of a structural damage with a maximum aberration of 3 cm. Furthermore, the crack development can be monitored by the RG59/U-6 cable sensor with a simple calibration.

• 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.).

• Journal of the Korean GEO-environmental Society
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• v.12 no.9
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• pp.35-45
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• 2011

This paper is to analyze the behaviors of tunnel support by TDR(Time Domain Reflectometry) sensor using electrical pulse. To analysis the behaviors of tunnel support, Copper tape as sensing materials was studied for on-site installation. Copper tape to the top of the glass tape, foam tape, and shielding the lower part was used electromagnetic shield sheet. For a high sensitivity to load and fill out the measurement noise emissions has been developed for the production of materials. This sensing material through the tunnel model tests for the change by surcharge load in TDR data were analyzed. Varing stiffness and support of conditions were determined the change of TDR data through PVC pipe tunnel section model tests. By comparing TDR data and finite element analysis, the behaviors of the tunnel support materials were analyzed qualitatively.