利用夫琅和费暗线探测自然光条件下的植被光合作用荧光研究

自然光照条件下测定的植被反射的辐照度光谱既包括太阳光诱导荧光的发射光谱，又包括叶片对入射光的反射光谱，研究如何从冠层光谱中提取荧光光谱有十分重要的应用价值。首先，论文介绍了夫琅和费暗线探测自然光条件下的光合作用荧光的基本原理和方法。其次，将太阳大气的夫琅和费暗线拓展到地球大气，发现地物光谱仪测定的冠层辐照度光谱中688nm和760nm两个氧气吸收形成的夫琅和费暗线特征明显，且荧光较强，所以利用这两个波段的夫琅和费暗线可以探测自然光条件下的光合作用荧光。第三，研究并分析了夫琅和费暗线方法计算的688nm和760nm波段的荧光特性，结果表明该方法计算的荧光是可靠的，它与光合有效辐射（PAR）关系密切，复相关系数达到了0．9；冬小麦冠层荧光光谱在760nm和688nm波段的荧光大小基本相等，而地锦冠层荧光光谱在688nm波段的荧光强度是760nm的3倍左右，表明荧光光谱能够更加敏感地反映植被物种或生理生化状况的差别。最后，将夫琅和费暗线方法计算的688nm和760nm波段的荧光数据与激光脉冲调制荧光仪测定Fv／Fm荧光参数进行了统计分析，结果表明它与Fv／Fm存在极显著的负相关关系。所以利用夫琅和费暗线方法能够探测植被冠层荧光，并有可能替代传统的测定方法，并推广到航空航天平台，实现荧光探测从接触式点测量方式到航空或卫星遥感大面积监测的技术飞越。

Detecting Photosynthesis Fluorescence under Natural Sunlight Based on Fraunhofer Line

The amount of chlorophyll fluorescence emitted by a leaf or canopy under natural sunlight is difficult to quantify because the signal is obscured by the reflected light.Firstly,the principle and method of separating the fluorescence emissive signal from canopy radiance spectrum based on Fraunhofer line was introduced.Secondly,the Solar Fraunhofer line was linked to the molecular oxygen absorption by the terrestrial atmosphere at 688nm and 760nm.The two Fraunhofer lines at 688nm and 760nm are obvious in the radiance spectra by ASD FieldSpec Pro NIR spectrometer,which largely overlap the chlorophyll fluorescence emission spectrum of leaves.Therefore,the two Fraunhofer lines at 688nm and 760nm could be selected to detect the emissive fluorescence.Thirdly,the statistical correlative coefficients(R~2) between PAR and emissive fluorescence of winter wheat and Parthenocissus tricuspidata at 688nm and 760nm reach 0.9.The emissive fluorescence of winter wheat at 688nm equals to that at 760nm,the emissive fluorescence of Parthenocissus tricuspidata at 688nm is 3 times larger than that at 760nm.Compared with canopy reflectance spectrum,fluorescence spectrum is more sensitive to species and plant stress conditions.Finally,the emissive fluorescence at 688nm and 760nm was related to F_v/F_m by a OS1-FL modulated chlorophyll fluorometer,the correlative coefficients are highly significant at 0.999 confident level,which means that the emissive fluorescence calculated from the two Fraunhofer lines at 688nm and 760nm could replace the modulated chlorophyll fluorometer method and be applied to airborne remote sensing.