NASA scientists have used satellites to measure what’s occurring inside plants at the cellular level, a finding that can help better crop assessment.

During photosynthesis, plants emit what is called fluorescence – light invisible to the naked eye but detectable by satellites orbiting hundreds of miles above Earth.

NASA scientists have now established a method to turn this satellite data into global maps of the subtle phenomenon in more detail than ever before.

Healthy plants use the energy from sunlight to perform photosynthesis, and re-emit some of that light as a faint but measurable glow.

Abundant fluorescence indicates active photosynthesis and a well functioning plant, while low or no fluorescence can mean that the plant is stressed or shutting down. Maps of the phenomenon give scientists a direct look at plant health.

The new maps – produced by Joanna Joiner of NASA’s Goddard Space Flight Center in Greenbelt, and colleagues – boast a 16-fold increase in spatial resolution and a three-fold increase in temporal resolution over the first proof-of-concept maps released in 2011 from a different satellite instrument.

Improved global measurements could have implications for farmers interested in early indications of crop stress and ecologists looking to better understand global vegetation and carbon cycle processes.

“For the first time, we are able to globally map changes in fluorescence over the course of a single month. This lets us use fluorescence to observe, for example, variation in the length of the growing season,” Joiner said.

Vegetation dynamics, including the northward migration of plant growth during the northern hemisphere springtime, is already observed indirectly by satellite data used measure the “greenness” of light reflected from Earth’s surface.

Fluorescence measurements complement the greenness measurements by providing direct and immediate information about plant productivity, researchers said.

Researchers saw plants start to shut down in the fall before their leaves turned colours. They also clearly detected early plant growth during the warm spring of 2012.

(This article was published on July 25, 2013)
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