When you’re working in the yard this summer, take a look up: Using a
satellite, NASA scientists are paying attention to how healthy your lawn and
garden are.
Next month, the agency plans to launch the Orbiting Carbon
Observatory-2. Its primary aim is to create a global map of carbon sources and
carbon sinks. The OCO-2 mission will provide the most detailed map of photosynthetic fluorescence
— that is to say, of how plants glow — ever created. Using this data,
scientists should be able to estimate how quickly the world’s plants are
absorbing carbon from the atmosphere.
During photosynthesis, a plant absorbs light, then immediately
re-emits it at a different wavelength. This is known as fluorescence. In a
laboratory setting, botanists can measure the intensity of fluorescence to
estimate how actively a plant is photosynthesizing. A satellite could, in
theory, detect the light emitted by the world’s plants to estimate how much
carbon the plants are absorbing. But there has always been a big, fiery
problem: the sun.
The sun is, in most ways, a nice thing to have around. It makes life
possible by supplying energy to our planet. From an observational standpoint,
though, it can be a major pain. There are huge swaths of the universe that we
simply cannot see because the brightness of the sun obscures our view.
In much the same way, the sun was thought to make it impossible to
measure global photosynthetic fluorescence. The signals we want to observe are
subtle and represent a narrow slice of the electromagnetic spectrum. The sun’s
broad-spectrum rays were presumed to overwhelm the wavelengths of plant
fluorescence, making them virtually impossible to detect.
That’s where NASA’s Joanna Joiner of the Goddard Space Flight Center
in Greenbelt, Md., and Christian Frankenberg of the Jet Propulsion Laboratory
in Pasadena, Calif., came in, with their innovative use of an electromagnetic
phenomenon known as Fraunhofer lines. In the early 19th century, German
optician Joseph Fraunhofer noticed that, in between the beautiful bands of
colored light that emerged from a prism, several dark lines appeared. That’s
because, by the time sunlight reaches Earth, molecules in the atmosphere have
absorbed certain wavelengths of light. In other words, our atmosphere blocks
out the sun in certain wavelength bands of the electromagnetic spectrum.
Joiner and Frankenberg realized that they could look for plant
fluorescence in the bands of the electromagnetic spectrum where the sun’s light
has been dimmed. Data from the Japanese Greenhouse Gases Observing Satellite,
which was launched in 2009, confirmed their hunch. Although the OCO-2 project
was already in motion by the time Joiner and Frankenberg made their
breakthrough, adding fluorescence readings will massively amplify the
satellite’s ability to carry out its carbon-measuring mission.
A detailed map of photosynthetic activity and carbon absorption will
better inform conservation efforts. It is widely believed that tropical forests
absorb approximately 20 percent of global carbon emissions from fossil fuel
combustion. But where else is carbon absorption highest? If the satellite data
detect other areas of intense photosynthetic activity, we ought to be working
hard to preserve them.
The carbon-uptake map should also help settle some long-running
disputes. Conventional wisdom once held that old-growth forests were bad at
carbon sequestration, because they seemed to be finished growing. Some analysts
suggested that turning those trees into houses or furniture would make room for
newer trees to absorb more carbon.
More recent findings, however, suggest that old trees continue to
breathe in carbon at high rates. OCO-2’s data will shed light, so to speak, on
the relative photosynthetic activity of old and new forests.
The data will also provide an early warning system. In 2005, for
example, a drought severely hampered the Amazon rain forest’s ability to absorb
carbon, but scientists didn’t realize the full scale of the impact for several
years. Satellite fluorescence data could have identified the situation almost
as it was happening.
There may not be much we can do to stave off a drought in the Amazon,
but there are other ways the data can be used. A decline in photosynthesis
rates, as identified by falling fluorescence, could alert farmers to crop
failure much earlier. It could help planners manage irrigation resources, as
well as alert global relief organizations to potential famines before they
happen.
Managing a garden from space sounds a bit futuristic, but horticulture
is about to enter the space age. From now on, you’re not just trying to impress
the neighbors with your green thumb.
More discoveries you might
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