In 2017, the group from the Optics of Photosynthesis Lab (OPL) developed a new method to measure a small but important signal produced by all plants, and in this case trees. This signal is called chlorophyll fluorescence and it is an emission of radiation at the visible and near-infrared wavelengths. Chlorophyll fluorescence relates to photosynthesis and the health status of plants, and it can be measured from a distance, for example from towers, drones, aircraft and satellites. Interpretation of the signal is, however, complicated, and so far it has only been possible to measure it within discrete spectral bands from fully-grown trees in the field.
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Source: Phys.org