Remote sensing of solar-induced chlorophyll fluorescence from an unmanned airship platform

The solar-induced chlorophyll (Chl) fluorescence (F) emitted by the photosynthetic machinery itself relates to photosynthetic efficiency closely. Passive remote sensing of ChlF at leaf level has been proved applicable. Large scale detection of ChlF is more difficult because the amount of ChlF represents less than 1% of the radiance of the vegetation under natural sunlight illumination. FLD (Fraunhofer Line Discriminator) and 3FLD have been used to extract ChlF. Both two methods require the incident solar irradiance. The incident solar irradiance and detection system are key problems at airborne level. Using unmanned airship platform and hyperspectral sensor, a viable detection system is built. Not only aFLD are discussed, this article also proposes a new method, a3FLD. The result shows that both aFLD and a3FLD can extract ChlF at the airborne level, but a3FLD achieved better results than aFLD when vegetation reflectance varies near the Fraunhofer lines.