Collaborative Research: Estimating Regional Forest Evapotranspiration and Photosynthesis with a Satellite Derived Vegetation Index and Surface Temperatue

目前的全球植被地图是由AVHRR卫星传感器提供的归一化差异植被指数(NDVI)绘制的。这些地图与吸收的太阳辐射或表面叶面积指数有关，但NDVI仅在理论上与植被的蒸散和光合作用过程有关，然后仅在最佳水和温度条件下才与之相关，这些限制严重限制了现实世界的应用。该项目将利用一个简单的森林蒸散和光合作用模型，完全由AVHRR数据驱动，该模型对次优的水和温度条件很敏感。研究人员将(1)将每周复合NDVI的季节趋势与植被物候和温度限制联系起来，(2)测试与树冠扩散阻力相关的卫星表面阻力系数，(3)定义基于生理的碳和水的能量质量转换系数。然后，将对照更复杂的生态系统过程模型对这些由NDVI驱动的模型进行评估。由此产生的卫星驱动的简单森林树冠模型应能极大地改进全球森林地表水和碳交换率的计算，并提高全球碳和水文预算的准确性。该项目的产出应有助于了解与“温室效应”有关的水、二氧化碳和气候从区域到全球的动态，并可能提供更好、更快速的手段来估计大规模的森林产量。调查人员相当有资格。为两位合作者提供的制度安排和支持都是极好的。生态系统研究计划建议支持这项为期三年的合作努力。

Current maps of global vegetation have been produced by the Normalized Difference Vegetation Index (NDVI) from the AVHRR satellite sensor. These maps have been related to absorbed solar radiation or surface leaf area index, but the NDVI has only been related theoretically to evapotranspiration and photosynthesis processes for vegetation and then only under optimal conditions of water and temperature, constraints that severely limit real world applications. The project will utilize a simple evapotranspiration and photosynthesis model for forests driven entirely by AVHRR data that is sensitive to sub-optimal water and temperature conditions. The investigators will (1) relate the seasonal trend of weekly composite NDVI to vegetation phenology and temperature limits, (2) test a satellite-derived surface resistance factor which is related to canopy diffusion resistance and (3) define physiologically based energy to mass conversion factors for carbon and water. These NDVI driven models will then be evaluated against a more complex ecosystem process model. The resulting simple, satellite-driven forest canopy models should allow a vastly improve computation of surface water and carbon exchange rates by global forests and improve accuracy of global carbon and hydrologic budgets. Output from the project should be useful in understanding the regional-to-global dynamics of water, CO2 and climate with regard to the "greenhouse effect" as well as possibly providing better, more rapid means of estimating forest production on large scales. The investigators are quite well qualified. Institutional accommodations and support for both collaborators is excellent. The Ecosystem Studies Program recommends support for this three- year collaborative effort.