地表遥感蒸散发模型研究进展

蒸散发(Evapotranspiration,ET)包括植被蒸腾与土壤蒸发,是地表能量平衡与水量平衡的重要组成部分,也是陆面过程研究的关键参数。卫星遥感技术的兴起,使获取大尺度非均匀下垫面的地表特征参数成为可能,一系列旨在精确估算地表实际蒸散量的遥感模型由此应运而生,以满足局地、区域乃至全球尺度蒸散发估算的需求。通过分析净辐射通量和地表与近地面大气层湍流热通量交换的方式,将遥感蒸散发模型分为单层模型和双层模型,总结其模型原理,讨论典型模型的优缺点及适用条件,分析蒸散发反演存在的遥感模型精度的图像范围依赖性和分辨率依赖性、时间尺度扩展及不确定性、模型验证以及地表辐射温度和阻抗5个问题。指出今后应加强地表温度反演精度、时间尺度扩展、有云日地表蒸散发、地面观测等方面的研究。

Progress in Remote Sensing-Based Models for Surface Heat and Water Fluxes

Evapotranspiration(ET),including evaporation from the soil surface and vegetation transpiration,is a critical component for water and energy balance on the Earth's surface,and an important parameter in land-surface processes. Satellites provide an unprecedented spatial distribution of critical land surface parameters such as surface albedo,fractional vegetation cover and land surface temperature,so numerous remote sensing-based models in conjunction with ancillary surface and atmospheric data have been developed to estimate local,regional and global ET. By analyzing turbulent heat flux between the surface and the near surface atmosphere,models for ET estimation using remotely sensed data are categorized as single-layer and two-layer models. A review of modeling principles is presented here,along with a discussion regarding the advantages and limitations of typical models and their applicability under varying vegetation cover and meteorological conditions. Issues involved in ET estimation such as domain dependence and resolution dependence of satellite-based ET models,temporal extension of instantaneous fluxes to ET at longer time scales with uncertainty,model validation,surface radiative temperature,and resistance are summarized and discussed. To improve the accuracy of ET estimation using remotely sensed data at regional scales,several problems must be resolved in the future. First,precision of land surface retrievals should be further improved. Second,improved methods for temporal extension of latent heat flux estimation are needed. Third,estimating ET under cloudy conditions is a challenging task in ET estimation at temporal scales. Four,accurate assessment of net radiative fluxes is critical. Last,ground calibration and observations of surface water and heat fluxes are crucial for the validation and improvement of remote sensing-based models.