荆条孤立冠层天空开度与太阳辐射透射率关系研究

为寻求用植物冠层分析仪（PCA）确定荆条灌丛孤立冠层太阳辐射的透射率，分别选择阴天和晴天条件，实测荆条灌丛下和裸地对照的太阳总辐射和散射辐射，以确定冠层的总辐射、散射辐射、直接辐射透射率。同时对荆条灌丛孤立冠层进行冠层分析，确定全部冠层的天空开度DIFN_总，以及-80°~+80°不同方位角方向的天空开度DIFN_总。以便对比分析冠层分析的天空开度与实测太阳辐射透射率的关系。结果表明，散射辐射透射率与冠层开度DIFN_总相关极为显著，相关系数接近于1；用DIFN_总计算的冠层下散射辐射比实测值低估了36.8%；太阳直接辐射所在方位的PCA冠层分析的DIFN_直与冠层下直接辐射的透过率关系密切，在-80°~+80°方位角范围内都呈抛物线型变化，-80°~0°范围内关系极为密切，而20°~+80°范围内DIFN_直偏低。PCA冠层分析确定的冠层天空开度DIFN_总可以用来确定冠层下的散射辐射；不同方位角的天空开度DIFN_直可以表达冠层下的太阳直接辐射透射率，这对解决冠层下太阳直接辐射无法测定的问题很有意义。

Solar Radiation Transmittance of Isolated Vervain Family Canopy Using Canopy Analyzer

For the purpose of searching for the route of determining the solar radiation transmittance rate through canopy analyzing by using plant canopy analyzer, PCA, the paper measured the total solar radiation and scattering radiation under vervain family canopy and over bare land under overcast and clear weather to determine the transmittance rates of total solar radiation, scattering solar radiation and direct solar radiation. At the same time the paper analyzed the vervain family canopy to determine diffusion non-interceptance (DIFN), divided as DIFN_total and DIFN_direct at -80°~+80°different solar radiation directions to analyze the relation between DIFN derived from canopy analyzing and solar radiation transmittance rates actually measured. The results showed that the transmittance rate of diffusion light had close relation with DIFN_total, the correlation coefficient almost equal to 1. The diffusion light intensity calculated by DIFN_total was 36.8% underestimated compared with those actually measured. There were close relations between the DIFN_direct at solar direct radiation direction analyzed by PCA and direct solar radiation transmittance rate, all of them changed according to parabolic curve at -80°~+80°azimuth angle. At -80°~0°azimuth angle, the DIFN_direct was almost the same to the direct solar radiation transmittance rate, and at 20°~+80°azimuth angle, DIFN_direct was lower. It was concluded that DIFN_total measured by PCA could be used to determine diffusion radiation under vervain family canopy. DIFN_direct of different azimuth angles could be used to express direct solar radiation transmittance rate. This is meaningful to solve the problem that the direct solar radiation under plant canopy can not be measured by instrument.