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.
The applications of the project are wide-ranging, but the science is easy enough to understand.
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.
Related: Special space series