Observation and estimate of net longwave radiation for improving evapotranspiration estimates

我测量了灌溉良好的草地上的净长波辐射，这是一个参考面，并显示了日本赤木宇都宫的辐射趋势。此外，为了提高参考蒸散量的估算精度，对长波净辐射方程中的系数进行了检验。结果表明：(1)长波净辐射呈现季节性变化，冬季辐射较大，夏季辐射较低；(2)日地表温度等于日气温的假设在全年难以适用。参考面的日平均地表温度夏季高于日平均气温，冬季低于日平均地表温度；(3)众所周知的长波净辐射方程的系数往往是气候变量，需要根据观测数据重新校准系数。

I measured net longwave radiation on the well-irrigated grassland, reference surface, and showed the tendency of the radiation at Utsunomiya, Tochigi, JAPAN. In Addition, I examined the coefficients of net longwave radiation equation for improving the estimation accuracy of the reference evapotranspiration. As the result, I revealed the following:(1) net longwave radiation shows seasonal variation with higher radiation in winter and lower radiation in summer; (2) the well-known assumption that the daily surface temperature is equal to the daily air temperature was hard to apply throughout the year. The daily mean surface temperature of the reference surface is higher than the daily mean air temperature in summer and lower than the daily mean surface temperature in winter; (3) the coefficients of well-known net longwave radiation equations tends to be the climate dependent variables and are required to re-calibrate coefficients based on the observation data.