High Latitude Microwave Remote Sensing and Modelling for Improved Predictive Understanding of Net Ecosystem Productivity in Boreal and Arctic Environment

加拿大北极-北方地区（ABR）的气温正在以惊人的速度上升，全球变化正在迅速改变这些地区的水、碳和能源循环，这些地区是重要的碳库。温度升高会改变ABR的碳平衡，并可能导致储存在土壤中的碳释放到大气中，从而产生重大的气候反馈。然而，重要的控制，如1）雪和冬季土壤热状况对冬季CO2排放的影响，2）土壤水分对总初级生产力（GPP）的影响和3）冻融循环对春季GPP和秋季呼吸的影响，在ABR中没有得到很好的量化，在生态系统模型中也没有得到很好的体现。我们对驱动这些控制的复杂相互作用的有限理解限制了我们准确预测ABR区域未来如何与大气相互作用，如何随着气候变化而演变以及如何影响人类活动的能力。 目前的星载无源微波辐射计对监测高纬度特征特别有用，因为它们可以测量了解和监测ABR中碳通量所需的关键变量（土壤湿度/温度、冻融循环和雪）。然而，在开发和验证关键表面变量的星载检索算法以及开发将PMRS观测纳入生态系统模型的方法以改进对高纬度碳通量的预测性理解方面仍然存在重大挑战。本研究计划的目标是开发微波遥感方法，以改善CLASS-CTEM（加拿大生态系统模型）模拟的关键表面变量影响ABR净生态系统生产力的三个重要控制：1）冬季土壤热状况对冬季CO2排放的影响2）土壤水分对总初级生产力的影响和3）冻融循环对GPP在春季和秋季CO2排放的影响。该方法充分利用了现场观测、微波遥感和生态系统模型（CLASS-CTEM）的互补性。特别是，拟议的计划将部署一个独特的空间分布的土壤呼吸监测系统和土壤水分/温度传感器在两个北极网站在加拿大，开发新的被动微波遥感检索算法和实施同化方法，通知CLASS-CTEM使用遥感观测。预期成果将填补与加拿大高纬度地区重要的气候变化反馈有关的科学空白，并将帮助政府、工业和土著社区制定适应气候变化的战略。

Temperatures are rising at disproportionally high rates across Canada's Arctic-Boreal Region (ABR) and global changes are rapidly altering the water, carbon and energy cycles in these regions that are important carbon pools. Rising temperatures alter the ABR's carbon balance and potentially lead to the release of the carbon stored in the soil to the atmosphere, creating major climatic feedbacks. However, important controls such as 1) the impact of snow and winter soil thermal regime on winter CO2 emission 2) the impact of soil moisture on gross primary production (GPP) and 3) the freeze/thaw cycle on GPP in spring and respiration in fall, are not well quantified in ABR and not well represented in ecosystem models. Our limited understanding of the complex interactions driving these controls limits our ability to accurately predict how ABR regions will interact with the atmosphere in the future, evolve with climate change and affect human activities. Current spaceborne passive microwave radiometers (PMRS) are particularly useful for monitoring high latitude characteristics, because they can measure key variables (soil moisture/temperature, freeze/thaw cycles and snow) needed to understand and monitor carbon fluxes in ABR. However, important challenges remain in developing and validating spaceborne retrieval algorithms of key surface variables and developing methodologies to ingest PMRS observations into ecosystem models in order to improve predictive understanding of carbon fluxes in high latitude. The goal of this research program is to develop microwave remote sensing approaches to improve CLASS-CTEM (Canadian ecosystem model) simulations of key surface variables affecting three important controls of ABR net ecosystem productivity: 1) winter soil thermal regime impact on winter CO2 emission 2) soil moisture impact on gross primary productivity and 3) freeze/thaw cycles impact on GPP in spring and fall CO2 emission. The methodological approaches take full advantage of the complementarity between in-situ observations, microwave remote sensing, and the ecosystem model (CLASS-CTEM). In particular, the proposed program will deploy a unique spatially distributed soil respiration monitoring system and soil moisture/temperature sensors at two arctic sites in Canada, develop new passive microwave remote sensing retrieval algorithms and implement assimilation approach to inform CLASS-CTEM using remote sensing observations. The expected outcomes will fill the scientific gaps related to important climate change feedbacks in Canada's high latitude regions and will help government, industry and Aboriginal communities to develop adaptation strategies to climate change.