玉米冠层辐射传输参数优化对陆气通量模拟的影响

Effects of Maize Canopy Radiative Transfer Parameters Optimization on Simulating Land-Atmosphere Flux Exchanges

设置合理的冠层辐射传输参数有利于地表能量过程的真实表达,将对改善陆面过程模型模拟精度起到重要作用。基于2008年和2012年锦州农田生态系统的通量、气象及生物因子连续观测,分析了玉米农田叶面积指数、植被覆盖度、平均叶倾角、叶片反射率和透射率动态变化规律及各因子间的关系,对CoLM模型辐射传输参数进行优化,并对模型优化效果进行定量评价。结果表明:叶面积指数与植被覆盖度和平均叶倾角分别呈幂函数和二次函数关系;平均叶倾角的参数优化对模型模拟几乎没有影响;叶片反射率和透射率优化后,冠层反照率模拟精度明显提高;净辐射、感热模拟值对实测值解释能力分别提高0.6%和4.0%,Nash-Sutcliffes系数增大0.008和0.028,相对均方差(RRMSE)减小0.068和0.050;潜热模拟精度改善程度小于感热,地表热通量未表现出改善。

A reasonable canopy radiative transfer parameters setting will play an important role in improving the simulation performance of land surface process model. This research was to investigate and assess the effects of optimized radiative transfer parameters in CoLM model on simulating land-atmosphere flux exchanges. Firstly, based on continuous observations of land-atmosphere flux exchanges, meteorological and biological elements from 2008 and 2012 at Jinzhou agricultural ecosystem research station, dynamic rules of maize field Leaf Area Index（LAI）, fraction of vegetation coverage（Fveg）, Mean Leaf Angle（MLA）, leaf reflectivity and transmissivity and their inter relationships were analyzed. Secondly, radiative transfer parameters in CoLM model were optimized with above the rules and relationships. Lastly, the effects of parameters optimization were quantificationally assessed with the criteria including Nash Sutcliffe（NS） and Relative Root Mean Square Error（RRMSE）. The results showed that LAI had power and quadratic relationships with Fveg and MLA, respectively. Model simulation precision was hardly any affected with optimization of MLA. On the contrary, with leaf reflectivity and transmissivity optimized, canopy albedo simulation precision was obviously increased, which improved the simulation performance of CoLM for net radiation and sensible heat flux with the explanatory ability of simulations to observations increased 0.6 and 4.0 percent, NS increasing 0.008 and 0.028 as well as RRMSE decreasing 0.068 and 0.050, respectively. However, simulation performance of latent heat flux improved lesser than sensible heat flux. Soil heat flux simulation was hardly improved.