Sinkyu Kang

Predicting spatial and temporal patterns of soil temperature based on topography, surface cover and air temperature

Soil temperature is a variable that links surface structure to soil processes and yet its spatial prediction across landscapes with variable surface structure is poorly understood. In this study, a hybrid soil temperature model was developed to predict daily spatial patterns of soil temperature in a forested landscape by incorporating the effects of topography, canopy and ground litter. The model is based on both heat transfer physics and empirical relationship between air and soil temperature, and uses input variables that are extracted from a digital elevation model (DEM), satellite imagery, and standard weather records. Model-predicted soil temperatures fitted well with data measured at 10 cm soil depth at three sites: two hardwood forests and a bare soil area. A sensitivity analysis showed that the model was highly sensitive to leaf area index (LAI) and air temperature. When the spatial pattern of soil temperature in a forested watershed was simulated by the model, different responses of bare and canopy-closed ground to air temperature were identified. Spatial distribution of daily air temperature was geostatistically interpolated from the data of weather stations adjacent to the simulated area. Spatial distribution of LAI was obtained from Landsat Thematic Mapper images. The hybrid model describes spatial variability of soil temperature across landscapes and different sensitivity to rising air temperature depending on site-specific surface structures, such as LAI and ground litter stores. In addition, the model may be beneficially incorporated into other ecosystem models requiring soil temperature as one of the input variables.

A regional phenology model for detecting onset of greenness in temperate mixed forests, Korea: an application of MODIS leaf area index

Abstract A regional phenology model for detecting onset of vegetation greenness was developed using year 2001MODIS land products in temperate mixed forests in Korea. The model incorporates a digital elevation model (DEM), moderate resolution imaging spectroradiometer (MODIS) landcover and leaf area index (LAI) products, and climate data from weather-monitoring stations. MODIS-based onset of greenness varied spatially and showed significant correlation with air temperature (r=−0.70, p

Improving continuity of MODIS terrestrial photosynthesis products using an interpolation scheme for cloudy pixels

The Moderate Imaging Spectroradiometer (MODIS) sensors onboard the NASA Terra and Aqua satellites provide the means for frequent measurement and monitoring of the status and seasonal variability in global vegetation phenology and productivity. However, while MODIS reflectance data are often interrupted by clouds, terrestrial processes like photosynthesis are continuous, so MODIS photosynthesis data must be able to cope with cloudy pixels. We developed cloud‐correction algorithms to improve retrievals of the MODIS photosynthesis product (PSNnet) corresponding to clear sky conditions by proposing four alternative cloud‐correction algorithms, which have different levels of complexity and correct errors associated with cloudy‐pixel surface reflectance. The cloud‐correction algorithms were applied at four weather stations, two fluxtower sites and the Pacific Northwest (PNW) region of the USA to test a range of cloud climatologies. Application of the cloud‐correction algorithms increased the magnitude of both daily and annual MODIS PSNnet results. Our results indicate that the proposed cloud correction methods improve the current MODIS PSNnet product considerably at both site and regional scales and weekly to annual time steps for areas subjected to frequent cloud cover. The corrections can be applied as a post‐processing interpolation of PSNnet, and do not require reprocessing of the MOD17A2 algorithm.

Ecotope mapping for landscape ecological assessment of habitat and ecosystem

An ecotope (spatial eco-space) map that considers topography and bio-organism-relevant variables emerges as an important basic framework when landscape-scale characteristics for ecosystem management and wildlife conservation are needed. A spatio-geoecological framework based on geographic information systems (GIS) and a vegetation survey were developed for wildlife habitat evaluation of national parks and applied to a representative rugged valley area of Mt. Sorak National Park in Korea. An ecotope map was classified into hundreds of types and dozens of groups by combining biological and geophysical variables. Variables included: forest vegetation type, topographic solar radiation, normalized difference vegetation index (NDVI), elevation, and anthropogenic factors, such as, streams and roads. Layers of GIS variables were produced by field surveys, modeling, satellite images, or digitalization. Vegetation surveys were carried out to identify finer-scale distribution of vegetation types in the rugged valley area. Digital forest vegetation maps from the Forestry Administrator were then modified using the field-surveyed vegetation maps. Topographic solar radiation was predicted with a daily topographic radiation model. The NDVI was calculated from the satellite imagery of a Landsat Thematic Mapper. A digital elevation model (DEM) was used and the other layers were digitized using topographical maps with a scale of 1:25 000. The aim of this study is to determine the geoecological factors relating to the spatial pattern of plant community. It was cleared by the spatial pattern of environmental variables and vegetation characteristics by detrended correspondence analysis using plant species and the environmental variables of each plot. The ordination component value of the first axis shows significant regression to some environmental variables. A case study of habitat evaluation was carried out using the resultant ecotope map. The spatial distribution of potential goral habitat and vegetation characteristics were predicted and the impact of human trails on the neighboring vegetation was also examined for restoration planning. The GIS-based framework developed for wildlife habitat evaluation is useful for natural resource management and human activity control in national parks in Korea.

Nitrogen removal from a riverine wetland: a field survey and simulation study of Phragmites japonica

Because Phragmites japonica is one of the dominant plant species in riverine wetlands in South Korea, we constructed an individual-based plant growth model to determine management strategies for maximizing nitrogen removal by P. japonica for water quality improvement purposes. We calibrated our model using field data on the growth, reproduction, and mortality of P. japonica individuals collected over one growing season in 1997 (May–October). The model effectively predicted seasonal changes in the number of the individuals (r 2 = 0.89), aboveground biomass (r 2 =0.85), and nitrogen concentration (r 2 =0.91). Total nitrogen, however, was poorly explained by our model (r 2 =0.53). To evaluate the effects of biomass removal (e.g. harvest or grazing) on Phragmites management strategies, removal was simulated by manipulating the intensity and period of biomass loss. Distinct patterns in population density and biomass were produced in intensity-period phase planes, suggesting that population dynamics are influenced by a strong relationship between disturbance intensity and period. In addition, the highest rates of nitrogen removal by P. japonica occurred for high-density populations that maintained relatively low biomass levels.

Retrievals of All-Weather Daily Air Temperature Using MODIS and AMSR-E Data

Satellite optical-infrared remote sensing from the Moderate Resolution Imaging Spectroradiometer (MODIS) provides effective air temperature (Ta) retrieval at a spatial resolution of 5 km. However, frequent cloud cover can result in substantial signal loss and remote sensing retrieval error in MODIS Ta. We presented a simple pixel-wise empirical regression method combining synergistic information from MODIS Ta and 37 GHz frequency brightness temperature (Tb) retrievals from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) for estimating surface level Ta under both clear and cloudy sky conditions in the United States for 2006. The instantaneous Ta retrievals showed favorable agreement with in situ air temperature records from 40 AmeriFlux tower sites; mean R2 correspondence was 86.5 and 82.7 percent, while root mean square errors (RMSE) for the Ta retrievals were 4.58 K and 4.99 K for clear and cloudy sky conditions, respectively. Daily mean Ta was estimated using the instantaneous Ta retrievals from day/night overpasses, and showed favorable agreement with local tower measurements (R2 = 0.88; RMSE = 3.48 K). The results of this study indicate that the combination of MODIS and AMSR-E sensor data can produce Ta retrievals with reasonable accuracy and relatively fine spatial resolution (~5 km) for clear and cloudy sky conditions.

Significance of aspect and understory type to leaf litter redistribution in a temperate hardwood forest

Annual production and redistribution of leaf litter were compared among three distinct understory patches in a temperate hardwood forest dominated by Quercus mongolica, Kalopanax pictus, Acer pseudo‐sieboldianum, and Carpinus cordata. Two patches were located on a southwest‐facing slope: one with an understory dominated by herbaceous plants (Patch S), and the other covered with evergreen dwarf bamboo, Sasa borealis (Patch SS). The third patch was on the opposite slope with an understory dominated by herbaceous plants (Patch N). Annual leaf litterfall was averaged 330 gm‐2 yr‐1 in the three patches from 1994 to 1998. From mid‐September 1996 to mid‐September 1997, net transport of leaf litter over patch boundaries was 1,824 g m‐1 from Patch S to SS, 1,465 g m‐1 from Patch S to N, and 886 g m‐1 from Patch SS to N. The amounts moving downslope out of Patch S, SS, and N were 2,548, 471, and 588gm‐1, respectively. When a mass balance approach was employed for the data of leaf litter transport, the results were ...

Evaluation of MODIS-derived Evapotranspiration at the Flux Tower Sites in East Asia

Evapotranspiration (ET) is one of the major hydrologic processes in terrestrial ecosystems. A reliable estimation of spatially representavtive ET is necessary for deriving regional water budget, primary productivity of vegetation, and feedbacks of land surface to regional climate. Moderate resolution imaging spectroradiometer (MODIS) provides an opportunity to monitor ET for wide area at daily time scale. In this study, we applied a MODIS-based ET algorithm and tested its reliability for nine flux tower sites in East Asia. This is a stand-alone MODIS algorithm based on the Penman-Monteith equation and uses input data derived from MODIS. Instantaneous ET was estimated and scaled up to daily ET. For six flux sites, the MODIS-derived instantaneous ET showed a good agreement with the measured data (

Transport and decomposition of leaf litter as affected by aspect and understory in a temperate hardwood forest

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Topographic and climatic controls on soil respiration in six temperate mixed-hardwood forest slopes, Korea

Transport of colored papers and decomposition of leaf litter of Quercus mongolica, Acer pseudo‐sieboldianum, and Kalopanax pictus were investigated on three patches differentiated by aspect and understory in a temperate hardwood forest. Two patches are represented by dwarf bamboo (Patch SS) and herbaceous plants (Patch S), respectively, lying on a southwest‐facing slope. The other patch (Patch N) is located on a northeast‐facing slope with herbaceous plants. Colored papers were placed on the patches to understand the pattern of litter movement on the ground. Papers were more dispersed in Patch S than in the other two patches. Some of the colored papers placed in Patch S moved upward. The results suggest that the litter movement is affected by aspect and that the leaf litter is retained by dwarf bamboo in Patch SS. Decay constant of Q. mongolica was significantly (p < 0.05) lower than those of K. pictus and A. pseudo‐sieboldianum. Decay rates of Q. mongolica were significantly different between Patches N and S and between Patches SS and S (p<0.05). On the other hand, decay rates of the other species were not significantly different among the three patches. The results suggest that aspect and understory exert an influence on redistribution and decomposition of leaf litter and that the effects could be different among the plant species.