Remote Sensing of Solar-Induced Chlorophyll Fluorescence at Atmospheric Oxygen Absorption Band Around 760 nm and Simulation of That Absorption in Laboratory

The present work establishes that the usual method of remote measurement of vegetation reflectance can also detect steady-state solar-induced fluorescence of vegetation. It identifies the hyperspectral signature of chlorophyll fluorescence as a small spike on the reflectance spectral curve of vegetation at the oxygen absorption (O₂-A) band around 760 nm. It justifies the origin of the fluorescence signature with both leaf- and pigment-level studies and quantifies it with the following: (1) presence/absence of chlorophyll in leaves; (2) varying concentration of chlorophyll in solution; (3) time of exposure under illumination; and (4) correctness of the calibration of leaf reflectance with respect to the standard white surface. The O₂-A band is detectable in solar radiation measured on Earth because of light absorption by the atmospheric oxygen column. This paper suggests an experimental technique to simulate that absorption in laboratory also. Oxygen gas compressed at high pressure can produce the oxygen absorption band artificially at indoor condition.