流域尺度土壤蒸发和植被蒸腾遥感估算与验证研究

Evapotranspiration (ET) and its partitioning between evaporation (E) and transpiration (T) is a key component of the water and energy cycle at all spatial scales, from field and watershed to regional and global, and is essential to many applications in climate, weather, hydrology, and ecology. Research suggests that T is likely to account for more than 80% of continental ET in order to maintain a mass balance between plant transpiration and CO2 uptake. In irrigated agriculture, quantification and management of ET and its components, E and T, is essential for reliable irrigation scheduling, improving water use efficiency and detecting plant stress, quantifying recharge and drainage, and yield forecasting. Operational application of the remote sensing-based two source energy balance model which can estimate ET and the components E, T of the land surface in different climates is potentially a viable tool for water resource management in watershed hydrology and agricultural irrigation. However, the energy flux partitioning process in two source energy balance model has not been adequately evaluated under a wide range of environmental conditions due to a dearth of reliable component temperatures and E and T measurements. This proposed project aims at investigating and potentially refining the two source energy balance algorithms for estimating of E and T using ground observations from soil lysimeter, sap flow and ratios of E/ET and T/ET estimated from isotope technology, and additionally from eddy covariance flux towers and large aperture scintillometers. The refined model is applied at watershed and regional scale, in combination with reconstructed MODIS land surface temperature and meteorological data simulated from Weather Research Forecast model for computing E and T. Finally the remotely sensed ET, E and T products using MODIS will be evaluated from the aggregation of ground patch scale E and T partitioned from eddy covariance system observed carbon dioxide and water vapor fluxes and ET from the larger aperture scintillometers measurements under different land cover conditions. The project will significantly contribute to improvements in the Two source energy balance model algorithms estimating land surface E and T under heterogeneous land surface and complex environmental conditions. It is also expected to provide improved methods for assessing the remotely sensed ET, E and T products at satellite scale.

地表蒸散是土壤-植被-大气系统中能量和水循环的重要环节，准确获取土壤蒸发和植被蒸腾将有助于更好地理解陆地生态-水文过程。地表蒸散发双层遥感估算模型已经在一些下垫面上进行了评估和应用，但是模型在复杂下垫面和不同气象条件下的适应性亟需进行验证。鉴于此本研究利用涡动相关仪、大孔径闪烁仪以及自动气象站等观测数据，优化地表蒸散发双层遥感估算模型高估土壤蒸发问题。利用经云下地面温度插补的MODIS 地表温度产品和WRF模拟的气象场数据，结合优化模型估算流域尺度时空连续土壤蒸发和植被蒸腾，并基于地面观测数据进行尺度扩展从而实现像元尺度模拟结果的真实性检验。本研究将完善地表蒸散发双层遥感估算模型，拓展模型在复杂下垫面和气象条件下的适用性、可靠性和稳定性，完善土壤蒸发和植被蒸腾遥感产品真实性检验过程中尺度不匹配问题。

地表蒸散是土壤-植被-大气系统中能量和水循环的重要环节，准确获取土壤蒸发和植被蒸腾将有助于更好地理解陆地生态-水文过程。项目按照要求生产了黑河流域2000-2016年1公里尺度，时空连续的地表蒸散发、土壤蒸发和植被蒸腾遥感产品，并无偿分享给相关科学研究者，以助他们顺利完成相关科研任务，并完成了2012-2016年黑河流域尺度上土壤蒸发和植被蒸腾遥感产品验证等工作。负责在重庆金佛山、山王坪、青木关、西南大学柑研所安装了20套树干液流计，并完成了数据的处理和分析工作。同时，项目利用MODIS遥感数据生产了流域尺度时空连续地表蒸散发、土壤蒸发和植被蒸腾遥感产品，并利用大孔径观测数据完成了像元尺度真实性检验；利用多角度热红外数据构建了多角度地表蒸散发遥感模型，模型估算地表蒸散发的精度要明显优于原模型；并利用蒸散发遥感产品实现西南地区干旱事件准确监测，并发现西南地区植被在夏季干旱期间出现变绿现象。相关研究成果已在Remote Sensing of Environment高水平期刊上发表第一标注研究论文2篇，Agricultural and Forest Meteorology期刊上发表第二标注研究论文1篇，国内核心期刊第一标注论文2篇。支持了黄晓娟、谭超和李秋苹完成学位论文，并顺利通过答辩。