基于遥感的区域蒸散量监测方法——ETWatch

ETWatch for monitoring regional evapotranspiration with remote sensing

ETWatch是用于区域蒸散遥感监测的业务化运行系统,集成了具有不同应用优势的遥感蒸散模型,并以Pen-man-Monteith公式为基础建立下垫面表面阻抗估算方法,利用逐日气象数据与遥感反演参数,获得逐日连续的蒸散分布图。所生成的从流域级到地块级的数据产品能动态反映区域蒸散发的时空变化规律。基于ETWatch方法,对2002-2005年海河流域和河北省馆陶县的蒸散状况进行了连续监测。利用地面观测资料对蒸散遥感监测产品的验证表明,涡度相关观测数据能量闭合率在0.9以上时,1 km级的日蒸散结果的平均偏差约10%;对于地块级(30 m)的ET,受混合像元的影响,相对于土壤水分消耗法测量的作物蒸散发,遥感监测作物蒸散发的平均误差在12.7%左右。

The remote sensing can provide surface parameters for Evapotranspiration （ET） estimation at regional scale, whereas the traditional approaches just provide points measurement. This paper introduces an ET monitoring system using remote sensing ETWatch, which is an operational processing chain starting from data pre-processing to application products, utilizing spatial information on climate, soil type, land use, vegetation cover, digital elevation, and remote sensed land surface parameters. The surface energy balance algorithm for land （SEBAL） and the surface energy system （SEBS） are integrated into ETWatch to estimate surface fluxes on clear-sky condition, while the Penmon-Monteith is applied to retrieved daily ET based on the surface resistence model, the meteorological data and the surface parameters from remote sensing. The application of ETWatch in Haihe basin is demonstrated for year 2002 to 2005, and a validation is carried by comparing the field fluxes measurement and the hydrological records with the model estimation. The results show that when the energy closure ratio （ECR） of eddy covariance （EC） technique is above 0.9, average deviation of daily ET at the I km scale is below 10% ; at the 30 m field scale, compared with water consumption from soil-moisture-depletion-method, average deviation of remote sensed daily crop ET is about 12.7%.