遥感反演瞬时地表蒸散发的日尺度扩展研究

Temporal upscaling of the remotely sensed instantaneous evapotranspiration (ET) is one of the hotspot and leading-edge issue in the quantitative remote sensing of surface ET. In light of the limitations in the existing methods of the temporal upscaling of remotely sensed instantaneous ET, after reviewing and summarizing the results from past studies, this project will first reveal the mechanisms of the interaction between surface ET and its main controlling and indicative factors by analyzing the diurnal and daily patterns of their variations, based on simulation data from the soil-vegetation-atmosphere transfer model and ground-based measurements. Using the results from the mechanism study, to improve the upscaled daily ET estimates, the project will then develop new methods of daily upscaling of surface ET under different sky conditions (clear sky at all times, clear sky at satellite overpass time but cloudy at other times, cloudy at satellite overpass time) and especially the method that can effectively take the impact of cloud cover into account. At the end, the developed upscaling methods will be applied to the instantaneous ET that is retrieved from the satellite remote sensing data. The estimated daily ET will be evaluated and validated using ground-based flux measurements. With the validation results, the developed ET upscaling methods will be updated and improved. The implementation of this project will help improve the study on the quantitative remote sensing of surface ET in China and satisfy the requirements in the agricultural information monitoring and water resources management.

遥感瞬时蒸散发时间尺度扩展是地表蒸散发定量遥感研究的热点问题与前沿课题之一。本项目针对遥感瞬时蒸散发日尺度扩展所存在的问题，在充分总结国内外已有研究基础上，利用土壤-植被-大气传输（SVAT）模型模拟数据，结合地面观测数据，探明地表蒸散发及其主要控制/表征因子的日变化规律和相互作用机理；在此基础上，发展出瞬时地表蒸散发在全天无云、卫星过境时刻无云（其他时刻部分有云）和卫星过境时刻有云3种状况下的日尺度扩展方法，重点解决不同云特征（云现时间、云层厚度、持续时间）对瞬时蒸散发日尺度扩展影响的问题，有效提高日尺度蒸散发估算精度；最后，开展卫星遥感数据的实际应用，通过地面观测通量数据的验证，对所发展的瞬时蒸散发日尺度扩展方法进行评估、修正和完善，确立一套精度可靠的瞬时蒸散发日尺度扩展新方法。通过本项目研究，能够提高我国地表蒸散发的定量遥感研究水平，满足国家农情监测、水资源管理等方面的需求。

遥感反演瞬时蒸散发的时间尺度扩展是地表蒸散发定量遥感研究的热点问题与前沿课题之一。本项目针对遥感反演瞬时蒸散发日尺度扩展所存在的问题，在充分分析地表蒸散发及其主要控制/表征因子的日变化规律和相互作用机理的基础上，首先创建了瞬时蒸发/蒸腾“两段分离法”，有效考虑了土壤表层和根区含水量对土壤蒸发和植被蒸腾的不同响应过程，完善了基于端元模型的土壤蒸发和植被蒸腾分离理论，提高了瞬时蒸散发的反演精度；利用Penman-Monteith方程，通过数学推导，建立了日尺度蒸发比与瞬时蒸发比的理论关系，并通过假定晴天条件下日尺度与瞬时解耦因子相等，提出了蒸散发日尺度扩展的“解耦因子不变法”，提高了瞬时蒸散发的日尺度扩展精度；分析了不同云覆盖对遥感瞬时蒸散发时间尺度扩展方法的影响，探寻了受云影响最小的时间尺度扩展方法。通过本项目研究，能够提供高精度日尺度蒸散发数据，提高我国地表蒸散发的定量遥感研究水平，满足国家农情监测、水资源管理等方面的需求。共发表科技论文20篇，其中SCI论文12篇，EI论文7篇，中文核心1篇；授权发明专利3项。