If you're working in the yard this summer, take a look: Using a satellite, NASA scientists are monitoring how healthy your lawn and garden are.
The agency plans to launch Orbiting Carbon Observatory-2 next month. The main goal is to create a global map of carbon sources and sinks. The OCO-2 mission will provide the most detailed map of photosynthetic fluorescence – that is, how plants glow – that has ever been created. This data should enable scientists to estimate how quickly plants in the world absorb carbon from the atmosphere.
The project's uses are broad, but science is easy to understand.
During photosynthesis, a plant absorbs light and immediately releases it again 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 doing photosynthesis. A satellite could theoretically capture the light emitted by the world's plants to estimate how much carbon the plants absorb. But there was always a big, fiery problem: the sun.
The sun is a beautiful thing in many ways. It makes life possible by supplying our planet with energy. However, from the point of view of observation, it can be a great pain. There are huge parts of the universe that we simply cannot see because the brightness of the sun obscures our view.
Similarly, it was believed that the sun made it impossible to measure global photosynthetic fluorescence. The signals we want to observe are subtle and represent a narrow section of the electromagnetic spectrum. It has been assumed that the broadband rays from the sun overwhelm the wavelengths of plant fluorescence, so that they are practically invisible.
This is where Joanna Joiner from NASA's Goddard Space Flight Center in Greenbelt, Md., And Christian Frankenberg from the Jet Propulsion Laboratory in Pasadena, California, came into play with their innovative use of an electromagnetic phenomenon called Fraunhofer Lines. In the early 19th century, the German optician Joseph Fraunhofer noticed that there were several dark lines between the beautiful colored light strips that emerged from a prism. This is because molecules in the atmosphere have absorbed certain wavelengths of sunshine until sunlight reaches Earth. In other words, our atmosphere blocks the sun in certain wavelength bands of the electromagnetic spectrum.
Joiner and Frankenberg realized that they could search for plant fluorescence in the bands of the electromagnetic spectrum in which the sunlight was dimmed. Data from the Japanese greenhouse gas observation satellite, launched in 2009, confirmed their belief. Although the OCO-2 project was already on the move when Joiner and Frankenberg made their breakthrough, the addition of fluorescence readings will massively improve the satellite's ability to perform its carbon measurement mission.
A detailed map of photosynthetic activity and carbon absorption will better inform conservation efforts. It is generally believed that tropical forests absorb about 20 percent of global carbon emissions from fossil fuel combustion. But where else is the highest carbon intake? If the satellite data recognizes other areas with intense photosynthetic activity, we should work hard to preserve them.
The carbon uptake map should also help resolve some longstanding disputes. Conventional wisdom once said that old growth forests were poor in carbon sequestration because they seemed to have finished growing. Some analysts suggested that converting these trees into houses or furniture would make room for newer trees to absorb more carbon.
However, more recent evidence suggests that old trees continue to inhale carbon at high speed. The data from OCO-2 will provide information about the relative photosynthetic activity of old and new forests.
The data also provide an early warning system. For example, a drought in 2005 severely affected the Amazon rainforest's ability to absorb carbon, but scientists haven't realized the full extent of the impact for several years. Satellite fluorescence data could have identified the situation almost as it happened.
We may not be able to do much to ward off a drought in the Amazon, but there are other ways that the data can be used. A drop in photosynthesis rates, as a result of declining fluorescence, could alert farmers to crop failures much earlier. This could help planners manage irrigation resources and alert global aid agencies to potential famines before they occur.
Managing a garden from space sounds a bit futuristic, but horticulture is about to enter the space age. From now on, don't just try to impress the neighbors with your green thumb.