• The Korean Journal of Applied Statistics
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• v.26 no.3
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• pp.511-520
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• 2013

Detection outliers and robust estimators are crucial in regression models with outliers. In such studies the focus is on detecting outliers and estimating the coefficients using leave-one-out. Our study introduces Rice estimator which is an error variance estimator without estimating the coefficients. In particular, we study a comparison of the statistical properties for Rice estimator with and without outliers in simple regression models.

• Journal of the Korean Data and Information Science Society
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• v.9 no.2
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• pp.189-202
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• 1998

The goat of this paper is to study on variance estimation - Rice variance estimation, Gasser, Sroka and Jennen-Steinmetz's varince estimation - in smoothing goodness-of-fit tests. The comparisons of powers on test statistics are conducted by the change of variance, the number of oscillations, the amplitude of the alternative sample distribution.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 1999.05a
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• pp.185-190
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• 1999

비모수 회귀모형에 있어서의 오차분산을 추정하는 방법들 중 차분에 기저한 방법(difference-based methods)을 이용한 기존의 추정량들을 비교 분석하는데 목적이 있다. 특히 점근적인 최적 이차차분에 기저한 Hall과 Kay, Titterington(1990)의 HKT 추정량에 대한 그들의 추정량에 대한 문제점들을 제시하고, HKT추정량과, GSJS 추정량, Rice 추정량에 대하여 모의실험을 이용하여 모수에 대한 수렴속도를 비교 분석하였다. 또한 GSJS 추정량에 대한 일치성과 수렴 속도를 보였다.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.1
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• pp.31-40
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• 2014

기후변화에 따른 기온상승과 강우패턴의 변화에 의한 농업의 취약성에 대한 연구는 주요 관심분야이다. 본 연구에서 기후변화가 한국의 2021~2040 (2030s), 2051~2070 (2060s) 및 2081~2100 (2090s)의 벼의 생산량과 관개요구량에 미치는 영향을 모의발생하여 분석 하였다. 세 가지 대표농도경로 (Representative Concentration Pathways: RCPs)에 대한 12개의 전지구 기후모형이 추정한 기후자료로부터 미래의 작물 물 요구량, 유효강우량, 관개요구량을 물수지 방법으로 계산하였다. Water Accounting Rice Model (WARM) 벼 작물모형을 보정하여 벼 생산량 추정에 이용하였다. 벼 생산량은 금세기 말에는 최대 40 %까지 감소하는 것으로 나타났다. 생산량은 특히 경남과 충남지방에서 크게 증가하는 것으로 나타났다. 생산량과 관개요구량의 시공간적인 불확실성을 분석한 바, 경북과 전남에서 2090s, RCP8.5때 불확실성이 가장 큰 것으로 나타났다. 미래에 일부 지역은 벼농사에 적합하지 않을 수도 있을 것으로 추정되었으며 기후변화 대응방안에 대한 연구가 필요할 것으로 판단된다.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.55 no.4
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• pp.312-318
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• 2010

This study was carried out to develop and test a prototype program that recommends the nitrogen topdressing rate using the color digital camera image taken from rice field at panicle initiation stage (PIS). This program comprises four models to estimate shoot N content (PNup) by color digital image analysis, shoot N accumulation from PIS to maturity (PHNup), yield, and protein content of rice. The models were formulated using data set from N rate experiments in 2008. PNup was found to be estimated by non-linear regression model using canopy cover and normalized green values calculated from color digital image analysis as predictor variables. PHNup could be predicted by quadratic regression model from PNup and N fertilization rate at panicle initiation stage with $R^2$ of 0.923. Yield and protein content of rice could also be predicted by quadratic regression models using PNup and PHNup as predictor variables with $R^2$ of 0.859 and 0.804, respectively. The performance of the program integrating the above models to recommend N topdressing rate at PIS was field-tested in 2009. N topdressing rate prescribed for the target protein content of 6.0% by the program were lower by about 30% compared to the fixed rate of 30% that is recommended conventionally as the split application rate of N fertilizer at PIS, while rice yield in the plots top-dressed with the prescribed N rate were not different from those of the plots top-dressed with the fixed N rates of 30% and showed a little lower or similar protein content of rice as well. And coefficients of variation in rice yield and quality parameters were reduced substantially by the prescribed N topdressing. These results indicate that the N rate recommendation using the analysis of color digital camera image is promising to be applied for precise management of N fertilization. However, for the universal and practical application the component models of the program are needed to be improved so as to be applicable to the diverse edaphic and climatic condition.

• Korean Journal of Remote Sensing
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• v.33 no.5_2
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• pp.721-732
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• 2017

With the increasing socio-economic importance of rice as a global staple food, several models have been developed for rice yield estimation by combining remote sensing data with carbon cycle modelling. In this study, we aimed to estimate rice yield in Korea using such an integrative model using satellite remote sensing data in combination with a biophysical crop growth model. Specifically, daily meteorological inputs derived from MODIS (Moderate Resolution imaging Spectroradiometer) and radar satellite products were used to run a light use efficiency based crop growth model, which is based on the MODIS gross primary production (GPP) algorithm. The modelled biomass was converted to rice yield using a harvest index model. We estimated rice yield from 2003 to 2014 at the county level and evaluated the modelled yield using the official rice yield and rice straw biomass statistics of Statistics Korea (KOSTAT). The estimated rice biomass, yield, and harvest index and their spatial distributions were investigated. Annual mean rice yield at the national level showed a good agreement with the yield statistics with the yield statistics, a mean error (ME) of +0.56% and a mean absolute error (MAE) of 5.73%. The estimated county level yield resulted in small ME (+0.10~+2.00%) and MAE (2.10~11.62%),respectively. Compared to the county-level yield statistics, the rice yield was over estimated in the counties in Gangwon province and under estimated in the urban and coastal counties in the south of Chungcheong province. Compared to the rice straw statistics, the estimated rice biomass showed similar error patterns with the yield estimates. The subpixel heterogeneity of the 1 km MODIS FPAR(Fraction of absorbed Photosynthetically Active Radiation) may have attributed to these errors. In addition, the growth and harvest index models can be further developed to take account of annually varying growth conditions and growth timings.

• Korean Journal of Environmental Agriculture
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• v.18 no.1
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• pp.1-5
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• 1999

This study was conducted to investigate methane emission among rice ecotypes in paddy soil (Jeonbug series). The varieties of rice involved early maturing short-grain variety, Samcheonbyeo, middle maturing variety, Hawsungbyeo and late maturing variety, Dongjinbyeo. The seasonal change of methane flux was high from ear formation stage to heading stage. It was found that the methane flux was tended to be lower in early maturing variety than in the mid-to-late maturing variety. The plots without rice straw reduced methane emission as much as 46% relative to rice straw application. The methane emission rate through rice stem was highly correlated with temperature fluctuation. Methane emission on ecotypes by rice straw application was 0.394 g $m^{-2}day^{-1}$ in early maturing variety (Samcheonbyeo), 0.407 g $m^{-2}day^{-1}$ in mid maturing variety(Hawsungbyeo), 0.411 g $m^{-2}day^{-1}$ in late maturing variety(Dongjinbyeo).

• KOREAN JOURNAL OF CROP SCIENCE
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• v.35 no.6
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• pp.518-524
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• 1990

Actual evapotranspiration was measured over rice paddy field by Bowen ratio heat balance method and based on this, investigated was the reliability of actual evapotranpiration estimation from Class-A Pan and small pan evaporation and reference evapotranspiration calculated by modified Penman-Monteith model. Crop coefficients based on Class-A Pan and small pan evaporation and reference evapotranspiration by modified Penman-Monteith model were averaged to be 1.57. 1.10 and 1.49 over the whole rice growing season, respectively. Their respective coefficients of variation were 28.7. 22.7 and 12.8 percent, respectively. Crop coefficient based on modified Penman-Monteith model varied in good agreement with the trend of leaf area development, being greatest around heading stage.

• Korean Journal of Soil Science and Fertilizer
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• v.28 no.3
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• pp.261-265
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• 1995

Methane flux from a rice paddy in Korea was measured to study the effects of water management and rice straw application on methane emission under different water managements ; flooding and intermittent irrigation, and with or without rice straw application. Methane emission ranged from 0.066 to $0.455g\;CH_4m^{-2}d^{-1}$. Intermittent irrigation has shown a mitigation effect of methane emission, 70% in NPK plot and 47% in NPK plus rice straw plot, relative to that of flooding. Methane emission from Korean paddy was estimated as 399,590tons per year assuming that paddy fields were managed under intermittent irrigation and rice straw application. This estimation was lower than that of OECD's by 56%, Neue's by 51%, and Matthew's by 62%, while higher than that of Taylor's by 118%.

• The Journal of Engineering Geology
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• v.29 no.4
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• pp.417-425
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• 2019

Agricultural groundwater use accounts for 51.8% of total groundwater use, so accurate estimation of groundwater use is important for efficient groundwater management. The purpose of this study is to develop a method for estimating the groundwater use of agricultural (rice farming and dry-field farming) wells using regression tree model based on the measured data of 370 wells. Three input variables of the model were evaluated as being significant: well depth, pipe diameter, and pump capacity, and the importance of each variable was 75% for well depth, 17% for pipe diameter, and 8% for pumping capacity. The daily usage of agricultural (rice farming and dry-field farming) wells by the regression tree model was estimated to be very similar to the actual usage, compared to the previous estimation method proposed by the Ministry of Construction and Transportation. In the future, it is expected that the reliability of the usage statistics will be improved if additional observed data is secured and this classification method is modified.