连续植被的热辐射方向性

The Thermal Radiant Directionality of Continuous Vegetation

正确认识非同温混合像元热辐射方向性规律是利用多角度遥感数据反演像元组分温度的前提。论文基于局地热平衡条件和组分有效发射率概念探讨了连续植被的热辐射方向性模型。模型表明同温下的热辐射方向性只决定于连续植被体系总有效发射率的方向性 ,它是各组分有效发射率的和 ,决定于植被叶面和土壤表面的发射率、冠层结构参数。在非同温状况下 ,组分温度通过组分有效发射率调节体系的辐射亮度方向变化。模型解释了热辐射中孔穴效应问题。并通过蒙特卡罗逆向模拟从微观探讨了热辐射方向性与植被叶面和土壤表面的发射率、冠层结构参数的关系 ,并对孔穴效应引起体系发射率的增量和辐射亮度的增量进行了模拟分析。结果表明 ,对于球面型连续植被 ,叶面和土壤表面发射率值分别取 0 .98和 0 .94时 ,垂直方向上孔穴效应使体系的总有效发射率有 0 .0 1— 0 .0 2 5幅度的增值。当连续植被处于 2 0℃同温状况时 ,孔穴效应引起的辐射亮度增量基本上都在 0 .8℃以上 ,最高可达到 1.3℃。

The correct recognition of radiant directionality of non isothermal mixed pixel is a precondition to its retrieval of component temperatrues. Based on the local thermal equilibrium and component effective emissivity concept the radiant model of continuous vegetation has been studied. The model shows that the radiant directionality of isothermal mixed pixel is fully dependent on that of whole effective emissivity of pixel, which is a function of component emissivities and the crown construct. For nonisothermal mixed pixel, the component temperatures play important role in adjustment of radiant directionality. The paper studies the relationship between the radiant directionality with leaf facet emissivity, soil surface emissivity, leaves area index ( LAI ) and leaves angle distribution ( LAD ) by Monte Carlo simulated results, it further analyses the whole effective emissivity and radiance increments caused by cave effects. Take the spherical type of LAD as an example, and set the values of leaf facet emissivity and soil surface emissivity to 0.98 and 0.94 respectively, the increment of whole effective emissivity ranges from 0.01 to 0.025 when value of LAI is set to more than 1.0 in nadir direction. When the vegetation and soil system is isothermal with 293K temperature, the radiant brightness temperature increment is more than 0.8K, the maximum is 1.3K caused by cave effects.