Remotely sensed blue and red fluorescence emission for monitoring vegetation

Abstract

For monitoring plant canopies, fluorescence signals emitted by plants underlaser or daylight excitation appear to be a promising tool among the various remote sensing techniques available. Chlorophyll fluorenscece is a nature emission exhibiting a broad inverse relation with the photosynthetic carbon assimilation of green plants. Besides this specific red fluorescence, a second emission with a comparable intensity is observed in the blue region of the spectrum, when the vegetation is excited by near-UV radiation. The origin of blue fluorescence is still under discussion, but increasing evidence is found to associate it with non-photosynthetic parts of the plant tissue including cellular wall components or precursors, skin waxes and vacuolar metabolites. Experimental results show that the blue fluorescence signal depends on the type of vegetation and is highly affected by stress. For a better characterization of vegetation, blue and red fluorescence should be considered simultaneously because they contain complementary information and are highly specific to vegetation. Two approaches, which are currently considered feasible for the remote detection of fluorescence signals, are analyzed and discussed: laser induced fluorescence (active remote sensing) and solar stimulated fluorescence (passive remote sensing).