Four-channel sensors for continuous remote sensing of carbon exchenge

要从机制上理解生物物理对碳交换的控制，就必须研究年内和年际气候趋势如何影响地表-大气交换。这项拟议的研究将量化北方生态系统和大气之间的二氧化碳净生态系统交换的动态。光能利用效率(LUE)将通过对吸收的光合作用有效辐射和总生态系统生产力的塔式测量得出。将使用一组微气象和生物物理变量来调查环境控制对每个地点LUE变化的影响。遥感植被指数已被证明在各种空间尺度上与LUE相关。因此，通量的放大将使用遥感技术的组合来实现。安装在塔上的辐射计将用于提供高分辨率的植被指数连续测量。植被指数和基于塔的通量之间的关系将从这些现场测量中得到发展。地面算法将应用于可比的基于卫星的指数，从而产生碳交换的生态系统规模估计。这项研究旨在提供更多关于推动大气生态系统交换的关键过程和环境作用力的知识，时间尺度从瞬时、季节性、年度到年际不等。因此，这里要求的传感器是一种通过在通量塔上安装便携式传感器以使空间面积与通量足迹的空间面积相当的高度来持续测量植被指数的手段。通过结合成对的下降流和上升流传感器，可以对植被指数进行连续测量，并将其平均到与二氧化碳通量数据相同的时间步长。

A mechanistic understanding of the biophysical controls on carbon exchange necessitates a study of how intra- and inter-annual climate trends affect surface-atmosphere exchanges. The proposed research will quantify the dynamics of net ecosystem exchange of carbon dioxide between a boreal ecosystem and the atmosphere. Light use efficiency (LUE) will be derived from tower-based measurements of absorbed photosynthetically active radiation and gross ecosystem productivity. The influence of environmental controls on the variation in LUE at each site will be investigated using the set of micrometeorological and biophysical variables. Remotely sensed vegetation indices have been shown to be correlated with LUE at a variety of spatial scales. Upscaling of fluxes will therefore be accomplished using a combination of remote sensing techniques. Tower-mounted radiometers will be used to provide high resolution continuous measurements of vegetation indices. Relationships between vegetation indices and tower-based fluxes will be developed from these field measurements. Ground based algorithms will be applied to comparable satellite-based indices resulting in ecosystem scale estimates of carbon exchange. The research is designed to provide increased knowledge of the critical processes and environmental forcings which drive the atmosphere ecosystem exchange on time scales ranging from instantaneous, seasonal, annual through inter-annual. The sensors requested here therefore represent a means to continuously measure vegetation indices by mounting portable sensors on the flux tower at a height such that the spatial area is comparable to that of the flux footprint. By incorporating pairs of downwelling and upwelling sensors, continuous measurements of the vegetation indices can be made and averaged to the same time step as the CO2 flux data.