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.