基于能量平衡的华北平原农田蒸散量的估算

通过测定冬小麦主要生育期农田冠层能量平衡的各分量、少风晴天时冠层温度和气温日变化及每周叶面积指数，分析了农田冠层能量平衡日变化规律、各分量季节变化特征，并以波文比系统实测蒸散值为相对标准，基于遥感冠层表面温度和能量平衡原理，采用Brown-Rosenberg公式对农田蒸散进行了估算和验证。结果表明：考虑夜间能量平衡各分量变化时，土壤热通量只占净辐射的3%左右，且夜间潜热交换值均很小，都在零左右波动；采用Brown-Rosenberg公式引入遥感冠层温度后估算的蒸散量较波文比系统实测值稍大，但忽略土壤热通量和考虑土壤热通量相比，二者相对平均偏差分别为16%和10%左右，差别不大，说明拔节-灌浆期（LAI≥3）估算蒸散时可近似忽略土壤热通量和夜间农田蒸散量，利用Brown-Rosenberg公式估算区域蒸散可行，该方法适用于华北平原农田蒸散计算。研究结果为将Brown-Rosenberg公式引入作物模型、基于热红外遥感冠层表面温度计算区域蒸散和水分胁迫系数进行区域估产提供了地面试验依据。

Evapotranspiration Estimation of Cropland in North China Plain Based on Surface Energy Balance Equation

In the main growth stages of winter wheat,the changes of every component of canopy energy balance by using Bowen-ratio system,diurnal pattern of canopy surface temperature and daily ambient air temperature in the clear days by using infrared thermometer,leaf area index every week were measured.The diurnal pattern and seasonal variation of canopy energy balance were analyzed.The evapotranspiration of the cropland was estimated by using Brown-Rosenberg method and validated by comparison with that measured using Bowen-ratio method,based on crop canopy temperature measured by remote sensing method and surface energy balance principle.The analysis of canopy energy balance indicated that the allocation of net radiation flux to soil heat flux was only about 3% when components of nocturnal canopy energy balance was considered.The latent heat flux in the nighttime was approximated to zero.The estimated evapotranspiration based on canopy temperature was slightly higher than that measured by Bowen-ratio system,and relative average deviations between the two methods were 16%(ignoring soil heat flux) and 10%(considering soil heat flux),with no significant differences.The results certified that the soil heat flux and nocturnal evapotranspiration of cropland can be ignored approximately in estimating cropland evapotranspiration during jointing stage and grain filling stage as LAI was above 3.It is feasible to estimate cropland evapotranspiration in the North China Plain by applying Brown-Rosenberg formula.The results justify the possibility for the combination of remotely sensed thermal infrared crop canopy temperature with crop growth model to estimate crop yield at the regional scale.