For decades, scientists have measured fluorescence in plants by exposing leaves to laser beams that, like black light, make fluorescence more apparent. Such experiments have revealed much about how certain types of plants fluoresce, but researchers have not been able to use lasers to measure the phenomenon across broad swaths of the Earth's surface.
To create their global fluorescence map, Joiner and her colleagues used a different technique. They analyzed an unusually dark section of the infrared portion of the solar spectrum embedded within a feature called a "Fraunhofer line." There is little background light at the line they focused on -- at about 770 nanometers -- which made it possible to distinguish the faint fluorescence signal.
The Future of Fluorescence
The new findings have implications for both current and upcoming satellite missions. In the near term, awareness of the fluorescence signal should help atmospheric scientists refine measurements of carbon dioxide and methane from the GOSAT mission.
The creation of the maps also bolsters the argument that an experimental mission being developed by the European Space Agency (ESA) -- the Fluorescence Explorer (FLEX) mission -- would make significant breakthroughs. The ESA is currently in the midst of feasibility studies and has not yet set a launch date for FLEX.
The findings also suggest that NASA's Orbiting Carbon Observatory-2 (OCO-2), a mission that is designed to measure carbon dioxide levels much like GOSAT, should be able to make useful fluorescence measurements on a global scale. OCO 2 will launch no earlier than February of 2013 from Vandenberg Air Force Base in California.
The maps, published online in the journal Biogeosciences, represent just a first attempt to detect terrestrial fluorescence on a broad scale and will be enhanced and expanded over time, the scientists involved in the project em
|Contact: Adam Voiland|
NASA/Goddard Space Flight Center