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Comparison of two remote sensing models for estimating evapotranspiration: algorithm evaluation and application in seasonally arid ecosystems in South Africa

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Journal of Arid Land 2019年第4期11卷 495-512页

作者： Sebinasi DZIKITI Nebo Z JOVANOVIC Richard Dh BUGAN Abel RAMOELO Nobuhle P MAJOZI Alecia NICKLESS Moses A ChO David C LE MAITRE Zanele NTShIDI h.rrison h.pienaar Council for Scientific and Industrial Research Natural Resources and Environment

Remote sensing tools are becoming increasingly important for providing spatial information on water use by different ecosystems. Despite significant advances in remote sensing based evapotranspiration(ET) models in recent years, important information gaps still exist on the accuracy of the models particularly in arid and semi-arid environments. In this study, we evaluated the Penman-Monteith based MOD16 and the modified Priestley-Taylor(PT-JPL) models at the daily time step against three measured ET datasets. We used data from two summer and one winter rainfall sites in South Africa. One site was dominated by native broad leaf and the other by fine leafed deciduous savanna tree species and C4 grasses. The third site was in the winter rainfall Cape region and had shrubby fynbos vegetation. Actual ET was measured using open-path eddy covariance systems at the summer rainfall sites while a surface energy balance system utilizing the large aperture boundary layer scintillometer was used in the Cape. Model performance varied between sites and between years with the worst estimates(R20.80 mm/d) observed during years with prolonged mid-summer dry spells in the summer rainfall areas. Sensitivity tests on MOD16 showed that the leaf area index, surface conductance and radiation budget parameters had the largest effect on simulated ET. MOD16 ET predictions were improved by:(1) reformulating the emissivity expressions in the net radiation equation;(2) incorporating representative surface conductance values;and(3) including a soil moisture stress function in the transpiration sub-model. Implementing these changes increased the accuracy of MOD16 daily ET predictions at all sites. however, similar adjustments to the PT-JPL model yielded minimal improvements. We conclude that the MOD16 ET model has the potential to accurately predict water use in arid environments provided soil water stress and accurate biome-specific parameters are incorporated.

关键词： MOD16 ET drought stress model validation Penman-Monteith Priestley-Taylor sensitivity analysis

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应具报的禽流感：南非的经验

应具报的禽流感：南非的经验

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第15届世界禽病大会、中国畜牧兽医学会2007年学术年会

作者： Anna C E pienaar 张培君 Directorate Animal health Department of Agriculture South AfricaP/Bag X138 Pretoria South Africa

南非是世界上最大的鸵鸟生产国,产品出口到全世界,鸵鸟被广泛养殖。迄今为止,南非没有爆发过需要申报的高致病性(h5N1亚型)禽流感,但是2004年和2006年鸵鸟发生过 h5N2亚型的高致病性禽流

关键词：禽流感高致病性

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