玉米群体辐射传输特征

实验观测分析了玉米群体总辐射的透过率、截获率、反射率和消光系数，结果表明玉米群体总辐射透过率、反射率和消光系数具有明显日变化特征；玉米雄穗开花前后其群体透过率和截获率有明显变化；日际反射率随玉米生育期而异，初期达0.23，之后逐渐下降至0.14左右；生育期平均反射率约为0.19；总辐射和净辐射的消光系数分别为0.51和0.41。提出了总体消光系数的概念，该系数在观测期较稳定，约为0.26，依此利用入射总辐射可算出作物群体冠层辐射截获量。

Characteristics of incoming radiation through maize canopy

The penetration,interception,reflectance and extinction coefficient of radiation of summer maize canopy are analyzed.The penetration,reflectance and extinction coefficient all show an obvious diurnal variation under clear sky;there are rema rkable changes for interception and penetration before and after flowering.The d aily reflectance decreases along with crop growing period,which is as high as 0. 23 at the initial stage and equal to 0.14 at the last growing stage.Over the who le growing period,the average is about 0.19.The canopy extinction coefficients f or incident short and net radiation are 0.51 and 0.41,respectively.A concept of bulk extinction coefficient is firstly introduced,which may be easily used to ca lculate the absorbed radiation by canopy.The variation of bulk extinction coeffi cient is more stable than that of the traditional extinction coefficient,on aver age,the bulk extinction coefficient is about 0.26.