• 한국농공학회논문집
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• 제61권5호
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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.).

• 한국농공학회:학술대회논문집
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• 한국농공학회 1998년도 학술발표회 발표논문집
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• pp.65-70
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• 1998

Soil moisture measuring is important for irrigation scheduling of upland crops, estimation of evapotranspiration, and hydrologic modeling. Hence, the comparative study was implemented for the soil moisture measuring instruments, Neutron probe and TDR with soil sampling methods, and the result was represented.

• 한국수자원학회논문집
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• 제32권3호
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• pp.215-223
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• 1999

최근, 국내외에서 TDR(Time Domain Reflectometry)기법을 이용한 토양 함수량 측정이 유용한 기술로써 받아들여져 오고 있다. Topp 등, (1980)에 의하여 최초로 제안된 경험식이 TDR에 의해 측정된 유전상수로부터 토양 함수량을 결정하는 데에 폭넓게 적용되어져 왔다. 그러나, 이 방법의 적용범위는 중간 입자 조성의 토양(Medium-testured soils)에 한해서 제한되어져 왔다. 본 연구에서는 Topp 모델이 사력토(Sandy-gravelly soils)에서도 적용가능한 지를 알아보고자 한다. 검정실험은 토양시료내에 설치된 2선 TDR 탐침을 따라 전송되는 광전자파의 전송시간 측정과 중력법에 따른 토양 함수량 결정의 두 부분으로 구성되었다. 실험에 사용된 토양시료는 2개의 다른 TDR 탐침길이에 대하여 중복시료로서 각 시료당 자갈의 질량 퍼센티지가 다른 7개의 입도 분포로 구성되었다. 계산 결과 Topp이 제안한 식은 주어진 유전상수에 대하여 3내지 8%정도 함수량을 과대 추정하고 있음을 알 수 있었으며, 본 연구에서 사력토에 대한 새로운 경험식을 제안하였다.

• 한국농공학회지
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• 제41권1호
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• pp.86-96
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• 1999

Laboratory experiment was performed for the TDR to measure the soil moisture, and the results, were compared with the design water content and the one measured by oven-try method. Sand and kaolinite were used . Varaiables for the experiment were water content (10-50%), void ration (0.7 -1.3), mixture rate of kaolinite (10-30%), and measurement methods (TDR and oven-dry). In all cases , TDR method showed very accurage and reliable results , and average error and error range were far lews than the oven-dry method which is widely used. Considerable error was noticed when water contnet was 50% where saturation was achieved for both methods. Therefore, TDR was thought to be applicable to the field moisture measurement if it is unsaturated. For field scale application of TDR, more research and verification of the accuracy with diverse soil conditions including physical ,chemical and mineral properties are recommended.

• 한국농공학회:학술대회논문집
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• 한국농공학회 1998년도 학술발표회 발표논문집
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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.

• 한국농공학회논문집
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• 제59권1호
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• pp.57-70
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• 2017

In this study, we evaluated daily root zone soil moisture dynamics and agricultural drought using a near-surface soil moisture data assimilation scheme with Soil Moisture Active & Passive (SMAP, $3km{\times}3km$) soil moisture footprints under different hydro-climate conditions. Satellite-based LANDSAT and MODIS image footprints were converted to spatially-distributed soil moisture estimates based on the regression model, and the converted soil moisture distributions were used for assessing uncertainties and applicability of SMAP data at fields. In order to overcome drawbacks of the discontinuity of SMAP data at the spatio-temporal scales, the data assimilation was applied to SMAP for estimating daily soil moisture dynamics at the spatial domain. Then, daily soil moisture values were used to estimate weekly agricultural drought based on the Soil Moisture Deficit Index (SMDI). The Yongdam-dam and Soyan river-dam watersheds were selected for validating our proposed approach. As a results, the MODIS/SMAP soil moisture values were relatively overestimated compared to those of the TDR-based measurements and LANDSAT data. When we applied the data assimilation scheme to SMAP, uncertainties were highly reduced compared to the TDR measurements. The estimated daily root zone soil moisture dynamics and agricultural drought from SMAP showed the variability at the sptio-temporal scales indicating that soil moisture values are influenced by not only the precipitation, but also the land surface characteristics. These findings can be useful for establishing efficient water management plans in hydrology and agricultural drought.

• Smart Structures and Systems
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• 제6권9호
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• pp.1007-1023
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• 2010

This paper describes the development and evaluation of an innovative TDR distributed moisture sensor. This sensor features advantages of being responsive to the spatial variations of the soil moisture content. The geometry design of the sensor makes it rugged for field installation. Good linear calibration is obtained between the sensor measured dielectric constant and soil physical properties. Simulations by the finite element method (FEM) are conducted to assist the design of this sensor and to determine the effective sampling range. Compared with conventional types of moisture sensor, which only makes point measurement, this sensor possesses distributed moisture sensing capability. This new sensor is not only easy to install, but also measures moisture distribution with much lower cost. This new sensor holds promise to significantly improve the current field instruments. It will be a useful tool to help study the influence of a variety of moisture-related phenomena on infrastructure performance.

• 한국농림기상학회지
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• 제7권1호
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• pp.78-90
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• 2005

각 지점의 강우 발생에 따른 토양수분의 감쇄 현상을 특성화 할 수 있는 감쇄 곡선의 경험식을 도출하였다. 시간에 따른 토양수분의 감쇄 곡선은 거의 모든 지점에서 지표와 지하에 걸친 토양수분 측정 자료들과 높은 일치성을 나타내었다. 각 사면에서의 감쇄 특성 을 살펴보면 사면 상부에서 하부로 내려올수록 추정된 감쇄 곡선에 보다 더 수렴하는 경향을 보였다. 또한 각 지점별로 감쇄 곡선이 각 강우에 대하여 재현되는 경향을 보여 각 지점에서 포화와 감쇄가 각 지점의 고유한 특성을 가지고 있음을 나타내었다. 또한, 강우 발생에 대한 토양수분의 감쇄와 충전 등의 사면의 특성화에 기준이나 지표로서의 습윤지수의 유의성을 확인할 수 있었다. 궁극적으로 사면 유출의 명확한 기작을 규명하는데 있어서 보다 더 객관적인 검증을 위하여 계절별, 연별과 같은 추가적인 토양수분의 측정과 정밀도 있는 자료의 분석이 필요할 것으로 사료된다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회
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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.

• 한국농공학회논문집
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• 제62권6호
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• pp.11-20
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• 2020

We estimated the spatio-temporally distributed soil moisture using Sentinel-1A/B SAR (Synthetic Aperture Radar) sensor images and soil moisture data assimilation technique in South Korea. Soil moisture data assimilation technique can extract the hydraulic parameters of soils using observed soil moisture and GA (Genetic Algorithm). The SWAP (Soil Water Atmosphere Plant) model associated with a soil moisture assimilation technique simulates the soil moisture using the soil hydraulic parameters and meteorological data as input data. The soil moisture based on Sentinel-1A/B was validated and evaluated using the pearson correlation and RMSE (Root Mean Square Error) analysis between estimated soil moisture and TDR soil moisture. The soil moisture data assimilation technique derived the soil hydraulic parameters using Sentinel-1A/B based soil moisture images, ASOS (Automated Synoptic Observing System) weather data and TRMM (Tropical Rainfall Measuring Mission)/GPM (Global Precipitation Measurement) rainfall data. The derived soil hydrological parameters as the input data to SWAP were used to simulate the daily soil moisture values at the spatial domain from 2001 to 2018 using the TRMM/GPM satellite rainfall data. Overall, the simulated soil moisture estimates matched well with the TDR measurements and Sentinel-1A/B based soil moisture under various land surface conditions (bare soil, crop, forest, and urban).