大豆和玉米冠层光合有效辐射各分量日变化

通过实测大豆和玉米冠层光合有效辐射各分量并计算其反射率、透射率,分析了各分量日变化规律及其影响因素。结果表明:光合有效辐射分量(FPAR)在一天中均接近于常数,特别是在8:00—11:00和14:00—16:00相对稳定;晴天大豆冠层入射光合有效辐射变化曲线较阴天平滑,反射率和透射率曲线没有阴天平滑;由于云层的吸收和散射作用,阴天中光合有效辐射(PAR)最大值的出现时间比晴天晚1h左右;植被冠层空间异质性对光合有效辐射各分量影响较大,不同作物类型的各分量之间有较大差异;大豆冠层空间异质性较玉米小,其光合有效辐射各个分量曲线较平滑;线性光量子传感器与太阳入射方向垂直投影线成30°时,冠层入射光合有效辐射平均偏离度值最小,为0.657%。

Diurnal changes of photosynthetically active radiation parameters in soybean and corn canopies

Based on the measurement of photosynthetically active radiation (PAR) parameters in soybean and corn canopies as well as the calculation of reflectance and transmittance, the diurnal changes of the parameters and their affecting factors were studied in this paper. The results showed that the fraction of photosynthetically active radiation (FPAR) in the whole day was approached to a constant, especially at 8:00 - 11:00 and 14:00 - 16:00. The incidence curve of PAR in soybean canopy was smoother in sunny day than in cloudy day, but the reflectance and transmittance curves were not. Due to the absorbing and dispersing of cloud, the maximum PAR occurred one hour later in cloudy day than in sunny day. The spatial heterogeneity in vegetation canopy affected the parameters significantly, which had larger differences between different crops. Soybean canopy had a smaller spatial heterogeneity, and thus, the curves of its PAR parameters were much smoother. When the angle between linear quantum sensor and solar incidence projection was 30 degree, the bias extent of measured PAR parameters was the least, being 0.657%.