In the future, the Goddard team expects that fluorescence measurements will complement existing measures of "greenness" in a variety of ways. They could help farmers respond to extreme weather or make it easier for aid workers to detect and respond to famines. Fluorescence could also lead to breakthroughs in scientists' understanding of how carbon cycles through ecosystems -- one of the key areas of uncertainty in climate science.
"What's exciting about this is that we've proven the concept," said Joanna Joiner, the deputy project scientist for NASA's Aura mission and the leader of the Goddard team that created the maps. "The specific applications will come later."
The same mechanism that makes plants fluoresce causes a range of everyday objects -- ground-up plant leaves, white shirts, jellyfish, and even blood and urine -- to glow intensely under black light.
However, plants fluoresce in specific parts of the blue, green, red, and far-red spectrum. Chlorophyll fluorescence from green foliage, for example, is produced at the red and far-red wavelengths.
"In plants, fluorescence is not something that you can see with your naked eye because background light overwhelms it," explained Joiner, the lead author of the paper. When sunlight strikes a leaf, disc-like green structures called chloroplasts absorb most of the light and convert it into carbohydrates through photosynthesis.
Chloroplasts re-emit about two percent of incoming light at longer, redder wavelengths. This re-emitted light -- fluorescent light -- is what the Goddard scientists measured to create their map. Fluorescence is different than bioluminescence, the chemically-driven mechanism lightning bugs and many marine species use
|Contact: Adam Voiland|
NASA/Goddard Space Flight Center