Most ecosystems and crops experience water stress in arid and semiarid areas of the Inner Mongolia grassland, Northern China. Yet the lack of long-term in situ monitoring data hinders the managerial capacity of changing water vapor environment, which is tied with sustaining the grassland in the Inner Mongolia. Environmental remote sensing monitoring and modeling may provide synergistic means of observing changes in thermodynamic balance during drought onset at the grassland surface, providing reliable projections accounting for variations and correlations of water vapor and heat fluxes. It is the aim of this paper to present a series of estimates of latent heat, sensible heat, and net radiation using an innovative first-principle, physics-based model (GEOMOD: GEO-model estimated the land surface heat with MODis data) with the aid of integrated satellite remote sensing and in situ eddy covariance data. Based on the energy balance principle and aerodynamics diffusion theory, the GEOMOD model is featured with MODIS (Moderate Resolution Imaging Spectroradiometer) data with 250 m spatial resolution to collectively reflect the spatial heterogeneity of surface properties, supplement missing data with the neighborhood values across both spatial and temporal domains, estimate the surface roughness height and zero-plane displacement with dynamic look-up table, and implement a fast iterative algorithm to calculate sensible heat. Its analytical framework is designed against overreliance on local micro-meteorological parameters. Practical implementation was assessed in the study area, the Xilin Gol River Basin, a typical grassland environment, Northern China. With 179 days of MODIS data in support of modeling, coincident ground-based observations between 2000 and 2006 were selected for model calibration. The findings indicate that GEOMOD performs reasonably well in modeling the land surface heat exchange process, as demonstrated by a case study of Inner Mongolia.
The autumn of 2007 has seen the most serious drought of last 30 years in the Poyang Lake Watershed (PLW, for short), which resulted in the sharp shrinkage of Poyang Lake from 3000 km2 of normal water coverage sharply to about only 50 km2 at drought peak. This paper adopted the data products of Moderate Resolution Imaging Spectroradiometer (MODIS, boarding on NASA satellites of Terra and Aqua) to analyze temporal process and spatial extension of this Drought in PLW. MODIS-derived Normalized Difference Water Deviation Index (NDWDI, for short) was calculated to examine the water balance of soil against background level, which was expressed with the NDWI average during 2000~2007. Though the Poyang Lake experienced sharp shrinkage in water area, the region near the Lake didn't show corresponsive serious water stress in NDWDI image series. This fact lies in that though the river runoff into the Lake decreased obviously, the soil of lake basin was exposed to less l water stress as the low terrain can easily supply water balance via ground flux.
KEYWORDS: Vegetation, MODIS, Climatology, Near infrared, Soil science, Temperature metrology, Short wave infrared radiation, Tantalum, Clouds, Data centers
Land surface temperature (LST) is widely thought to closely relate with vegetation cover (often expressed with VI, i.e.
vegetation index), and the negative LST/VI relationship is often used to estimate LST. However, this issue hasn't reached
academic agreement yet as the LST/VI relation isn't linear, static and independent of other factors. This study examined
the temporal variation of LST/VI relation and its link with soil moisture with multi-phase MODIS products. The result
indicates that in the regions of high latitude where the condition of thermal energy is among ecologic limiting factors, the
negative LST/VI relation doesn't hold true. The study also proves that the LST/VI association depends on soil moisture,
which further complicates their relationship. This examination underlines that when the LST/VI slope is used to estimate
LST, the uncertainty of LST/VI relation and the influence of soil moisture should both be carefully take into accounts.
The surface heterogeneity of densely vegetated region is often ignored as its spatial variation doesn't shows so obvious as sparse region. This paper is to examine to which degree the estimation difference with scale change would be. The surface net radiation and related variables between six consecutive scales from 30 to 960 m over a dense grass covered region in Northern China are calculated with a simplified scheme based on Landsat ETM data. The estimation agreements between neighbouring scales are evaluated with the mean absolute percent difference and the index of agreement. The two indices indicated variation is not so obvious and can't determine whether the study area is homogeneous or not. Further analyses of the fraction variation of land covers with scales and the change of related mean variables for individual land cover with scales, reach a consistent result that the major covers with larger patches are more insensitive to scale change than the minor ones with smaller patches. The introduction of land cover information improves detecting the effect of patches with different covers when the surface net radiation is considered.
The Tibetan Plateau is among the fewest extensive regions remote far from the influences of human activities. It provides an ideal site to study the response of vegetation cover to water/thermal (WT) conditions, esp. the response of natural vegetation cover. The paper aims to discuss the spatial variation and then the relations of WT climate elements with satellite derived NDVI. The discussion is taken with the supports of ground climatic observation data and AVHRR NDVI product (8 Km) from year 1982 to 2000, in central and east Tibetan Plateau where the gauge is basically dense enough to qualify related analyses. Based on the simulation of egetation spatial distribution trend surfaces, the transect comparison of different directions and the work of vegetation grouping, the relationships between NDVI and precipitation (N-P for short), between NDVI and temperature (N-T for short) are respectively investigated and analyzed, both spatially and biologically. The results presented by this study indicate that in central/east Plateau annual mean NDVI is less influenced by WT conditions if the covered vegetation is dense and evergreen or totally sparse; the N-T and N-P values of peripheral Plateau regions are low while the values of main plateau body are higher than 0.75; in addition, altitude tends to play an obvious negative role in the spatial distribution of thermal condition, and then in the distribution of vegetation cover.
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