• Ocean and Polar Research
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• 제30권3호
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• pp.313-324
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• 2008

In order to understand the variation of ENSO-related oceanic environments in the tropical and North Pacific Ocean, spatio-temporal variations of sea surface temperature anomaly (SSTA) and sea surface height anomaly (SSHA) are analyzed from distributions of complex empirical orthogonal functions (CEOF). Correlations among warm pool variation, southern oscillation index, and ocean surface currents were also examined with respect to interannual variability of the warm pool in western tropical Pacific. Spatio-temporal distributions of the first CEOF modes for SSTA and SSHA indicate that their variabilities are associated with ENSO events, which have a variance over 30% in the North Pacific. The primary reasons for their variabilities are different; SST is predominantly influenced by the change of barrier layer thickness, while SSH fluctuates with the same phase as propagation of an ENSO episode in the zonal direction. Horizontal boundary of warm pool area, which normally centered around $149^{\circ}E$ in the tropics, seemed to be expanded to the middle and eastern tropical regions by strong zonal currents through the mature phase of an ENSO episode.

• 대한원격탐사학회지
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• 제33권1호
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• pp.47-60
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• 2017

The permafrost active layer plays an important role in permafrost dynamics. Ecological patterns, processes, and water and ice contents in the active layer are spatially and temporally complex depending on landscape heterogeneity and local-scale variations in hydrological processes. Although there has been emerging interest in the application of optical remote sensing techniques to permafrost environments, optical sensors are significantly limited in accessing information on near surface geo-cryological conditions. The primary objective of this study was to investigate capability of L-band SAR data for monitoring spatio-temporal variability of permafrost ecosystems and underlying soil conditions. This study exploits information from different polarimetric SAR observables in relation to permafrost environmental conditions. Experimental results show that each polarimetric radar observable conveys different information on permafrost environments. In the case of the dual-pol mode, the radar observables consist of two backscattering powers and one correlation coefficient between polarimetric channels. Among them, the dual-pol scattering powers are highly sensitive to freeze/thaw transition and can discriminate grasslands or ponds in thermokarst area from other permafrost ecosystems. However, it is difficult to identify the ground conditions with dual-pol observables. Additional backscattering powers and correlation coefficients obtained from quad-pol mode help understanding seasonal variations ofradar scattering and assessing geo-cryological information on soil layers. In particular, co-pol coherences atHV-basis and circular-basis were found to be very usefultools for mapping and monitoring near surface soil properties.

• Ocean and Polar Research
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• 제32권3호
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• pp.187-201
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• 2010

The purpose of this study was to investigate the temporal and spatial variability of taxonomic groups and major species of the mesozooplankton community in Lake Shihwa, Korea. Monthly collections were carried out at five stations in Lake Shihwa for a period of one year. The mesozooplankton community showed distinct seasonal variability with water temperature and salinity. Major mesozooplankton species in each seasonal community were derived from non-metric MDS and SIMPER as follows: winter community (Acartia hongi and Eurytemora pacifica), spring community (Acartia hudsonica and Polychaeta larvae), summer community (Acartia sinjiensis, Pavocalanus crassirostris, Evadne tergestina and Cirripedia nauplii) and fall community (Paracalanus indicus and Podon leuckarti). The succession of the seasonal species, A. hudsonica and A. sinjiensis, was the most remarkable event during the seasonal changes of the mesozooplankton community. The species response curve of these species fitted with the logistic regression in relation to water temperature and salinity. The curve also correctly represented the characteristics of the occurrence of A. hudsonica and A. sinjiensis in Lake Shihwa.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2021년도 학술발표회
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• pp.141-141
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• 2021

This study proposed an equation for Rainfall Threshold for Flood Warning (RTFW) for urban areas based on computer simulations. First, a coupled 1D-2D dual-drainage model was developed for nine watersheds in Seoul, Korea. Next, the model simulation was repeated for a total of 540 combinations of the synthetic rainfall events and watershed imperviousness (9 watersheds × 4 NRCS Curve Number (CN) values × 15 rainfall events). Then, the results of the 101 simulations with the critical flooded depth (0.25m-0.35m) were used to develop the equation that relates the value of RTFW to the rainfall event temporal variability (represented as coefficient of variation) and the watershed Curve Number. The results suggest that 1) the rainfall with greater temporal variability causes critical floods with less amount of total rainfall; and that 2) the greater imperviousness requires less rainfall to have critical floods. For validation, the proposed equation was applied for the flood warning system with two storm events occurred in 2010 and 2011 over 239 watersheds in Seoul. The results of the application showed high performance of the warning system in issuing the flood warning, with the hit, false and missed alarm rates at 68%, 32% and 7.4% respectively for the 2010 event and 49%, 51% and 10.7% for the event in 2011.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2021년도 학술발표회
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• pp.134-134
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• 2021

Precipitation is a crucial component of water cycle and play a key role in hydrological processes. Traditionally, gauge-based precipitation is the main method to achieve high accuracy of rainfall estimation, but its distribution is sparsely in mountainous areas. Recently, satellite-based precipitation products (SPPs) provide grid-based precipitation with spatio-temporal variability, but SPPs contain a lot of uncertainty in estimated precipitation, and the spatial resolution quite coarse. To overcome these limitations, this study aims to generate new grid-based daily precipitation using Automatic weather system (AWS) in Korea and multiple SPPs(i.e. CHIRPSv2, CMORPH, GSMaP, TRMMv7) during the period of 2003-2017. And this study used a machine learning based Random Forest (RF) model for generating new merging precipitation. In addition, several statistical linear merging methods are used to compare with the results of the RF model. In order to investigate the efficiency of RF, observed data from 64 observed Automated Synoptic Observation System (ASOS) were collected to evaluate the accuracy of the products through Kling-Gupta efficiency (KGE), probability of detection (POD), false alarm rate (FAR), and critical success index (CSI). As a result, the new precipitation generated through the random forest model showed higher accuracy than each satellite rainfall product and spatio-temporal variability was better reflected than other statistical merging methods. Therefore, a random forest-based ensemble satellite precipitation product can be efficiently used for hydrological simulations in ungauged basins such as the Mekong River.

• The Korean Journal of Ecology
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• 제24권6호
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• pp.353-357
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• 2001

Differential response of genotypes to temporal environmental heterogeneity may contribute to the long-term persistence of these genotypes within a population. In this experiment, we experimentally tested whether groups by season interactions for germination and seedling growth can explain genetic variability within the population. To determine whether seeds collected during the four seasons respond differentially to temperature treatments, two-way ANOVA was performed. This study indicates that seasonal environments have large effects on demography. Groups within populations respond differentially to seasonal environments by influencing population growth that may in turn influence community composition. Most importantly, the study showed that temporal heterogeneity in the environment might functions as a mechanism that maintains within-population genetic diversity.

• 한국수자원학회논문집
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• 제38권7호
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• pp.517-526
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• 2005

현재 우리나라에서 주로 사용되는 지하수 함양량 추정방법은 지하수 감수곡선에 의한 기저유출분리법과 관측공의 자료를 이용한 지하수위 변동법으로 대별된다. 기저유출분리법은 연단위기반의 집중형 개념의 접근법을 사용하며, 지하수위변동곡선해석법은 유역단위의 물수지 개념보다는 국지적인 지하수 관측정의 변화에 주로 의존하고 있다. 한편 지하수 함양량은 기후조건, 토지이용, 관개와 수리지질학적 비균질성에 의해 현저한 시공간적 변동성을 나타내고 있어서 위의 두 가지 방법으로는 이같은 특성을 고려하는데 여러 가지 한계를 보인다. 이에 본 연구에서는 준분포형 강우-유출모형인 SWAT모형을 이용하여 공간적변동성을 고려한 일단위 함양량 산정기법을 제시하였다. 이 방법을 이용하면 기존의 유역 대표 함양량 대신 각 소유역의 비균질한 특성을 반영한 함양량의 분포를 산정할 수 있다. 산정된 일단위 함양량은 기후조건 토지이용 및 수리지질학적 비균질성과 토양층에서의 지체등 물리적인 거동까지 반영된 것이어서 기존의 간접적 추정방식에 의한 연단위 함양률을 크게 개선할 수 있을 것으로 기대된다.

• Spatial Information Research
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• 제16권4호
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• pp.467-478
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• 2008

본 연구에서는 서울지역에서 기온($^{\circ}C$) 및 강수(mm)의 시 공간 구조 분석 및 변화경향과 변이성을 도출하였다. 1997년 1월부터 2006년 12월까지의 기상청에서 제공하는 31개 자동기상관측망의 기온 및 강수자료를 이용하였으며, 미 관측지점의 값을 추정하기 위하여 거리자승역산가중 (IDSW: Inverse Distance Squared Weighing)을 적용하여 보간 하였다. 기온과 강수량의 변이성을 평가하기 위하여 연평균 및 더운 날과 추운 날의 빈도를 알아보았다. 그 결과 최고 기온 값은 1999년의 $32.80^{\circ}C$, 최저기온은 2001년의 $-19.94^{\circ}C$로 나타났다. 더운 날의 빈도가 가장 많았던 해는 79일을 기록한 2006년이며, 2004년과 2005년에도 비슷한 기록을 보였다. 추운날의 빈도가 가장 많았던 해는 105일을 기록한 2001년이다. 또한 기온과 강수량 모두 지난 10년 동안 기온이 약 $1.03^{\circ}C$, 강수량이 약 483.09mm 증가한 것으로 나타났다. 과거 10년 동안 기온변이의 경우 고도가 높은 산림지역과 고도가 낮은 주거지역에서 차이가 크게 나타난 반면, 강수량의 경우 지형 및 토지이용에 따른 변이성의 차이가 미미한 것으로 나타났다.

• 한국수산과학회지
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• 제52권6호
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• pp.719-724
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• 2019

This study is an extension of our previous model for a size-based fish stock assessment. In the previous model, we applied an allometric length-weight relationship (W=α·L^β) to convert lengths of fish to weights, and estimated those parameters α and β, using data about lengths and weights aggregated over years. In this study, we focused on whether consideration of temporal (e.g., year-to-year) variability in those estimates (i.e., ${\hat{\alpha}}$ and ${\hat{\beta}}$) would contributive. After calculating year-specific estimates (i.e., year-specific pairs of ${\hat{\alpha}}$ and ${\hat{\beta}}$) by applying data about lengths and weights separated by year, we evaluated the contribution of those year-specific pairs of ${\hat{\alpha}}$ and ${\hat{\beta}}$ to the performance of the size-based stock assessment model. The model with such year-to-year variability being considered (lower AIC) outperformed that with the variability being ignored (higher AIC). We illustrated this study using data on Korean chub mackerel Scomber japonicus from 2005-2017.

• 한국환경생태학회지
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• 제28권1호
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• pp.24-32
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• 2014

본 연구는 2011년~2013년 사이에 춘천시에 위치하고 종적으로 분포하는 2개 하천(공지천, 신촌천)을 대상으로 각각 2개의 조사 지점에서 저서성 대형무척추동물 군집의 계절 및 공간별 조사를 시행하였다. 본 연구는 하천에서의 인위적인 교란이 저서성 대형무척추동물의 종수 및 개체수의 감소에 미치는 영향을 고찰하였다. 본 연구의 상류구간인 신촌천(St.1, St.2)과는 달리 공지천 구간(St.3, St.4)은 공지천생태하천조성사업의 진행에 따른 인위적인 교란에 빈번하게 노출된 구간이었다. 이 사업 이후 물 흐름의 정체시간이 장기화됨으로 인하여 2012년 하절기에 신촌천 상류(St.1)와 공지천 하류(St.4) 사이에 커다란 수온의 차이(최대 $9^{\circ}C$까지) 및 $30^{\circ}C$ 이상 수온이 증가하는 현상을 보였다. 또한 매년 몬순강우는 저서성 대형무척추동물의 종수 및 개체수 그리고 종 다양도지수의 감소를 초래하였다. 분류군에 따른 우점 양상을 보면, 신촌천 상류에서만 날도래류가 우점하였을 뿐, 그 외의 지점들에서는 파리류가 우세하게 출현하였다. 저서성 대형무척추동물의 시 공간적인 변동은 인위적인 하상의 교란(하상변화, 수온 증가) 및 몬순강우 등으로 인한 토사유입과 같은 물리적인 요인들의 영향을 반영하는 지표생물로서 중요하다.