US: Data from satellite sensors show that during the Northern Hemisphere's growing season, the Midwest region of the United States boasts more photosynthetic activity than any other spot on Earth, according to NASA and university scientists.
Healthy plants convert light to energy via photosynthesis, but chlorophyll also emits a fraction of absorbed light as a fluorescent glow that is invisible to the naked eye. The magnitude of the glow is an excellent indicator of the amount of photosynthesis, or gross productivity, of plants in a given region.
Research in 2013, led by Joanna Joiner of NASA's Goddard Space Flight Center in Greenbelt, demonstrated that fluorescence from plants could be teased out from existing data from satellites that were designed and built for other purposes. The new research, led by Luis Guanter of the Freie Universität Berlin, used the data for the first time to estimate photosynthesis from agriculture. Results were published on 25 March in the Proceedings of the National Academy of Sciences.
Above: The magnitude of fluorescence portrayed in this visualisation prompted researchers to take a closer look at the productivity of the U.S. Corn Belt. The glow represents fluorescence measured from land plants in early July, over a period from 2007 to 2011. Image credit: NASA's Goddard Space Flight Center
Guanter, Joiner and Frankenberg launched their collaboration at a 2012 workshop, hosted by the Keck Institute for Space Studies at the California Institute of Technology (Caltech) in Pasadena, to explore measurements of photosynthesis from space. The researchers set out to describe the phenomenon observed by carefully interpreting data from the Global Ozone Monitoring Experiment 2 (GOME-2) on Metop-A, a European meteorological satellite. Data showed that fluorescence from the U.S. Corn Belt peaks in July at levels 40 percent greater than those observed in the Amazon. Comparison with ground-based measurements from carbon flux towers and yield statistics confirmed the results.
Ground-based measurements have a resolution of about 0.4 square mile (1 square kilometer), while the satellite measurements currently have a resolution of more than 1,158 square miles (3,000 square kilometers). The study confirms that even with coarse resolution, the satellite method could estimate the photosynthetic activity occurring inside plants at the molecular level for areas with relatively homogenous vegetation like the Corn Belt.
Challenges remain in estimating the productivity of fragmented agricultural areas not properly sampled by current space-borne instruments. That's where missions with better resolution could help, such as NASA's Orbiting Carbon Observatory-2 (OCO-2) — a mission planned for launch in July 2014 that will also
According to Frankenberg, the remote sensing-based techniques now available could be a powerful monitoring tool for food security, especially data from OCO-2 in combination with data from other upcoming satellites such as NASA's Soil Moisture Active Passive (SMAP), scheduled for launch later this year.
Source: NASA's Jet Propulsion Laboratory