Terra Turns Five

Five years ago NASA’s Terra satellite began measuring Earth’s vital signs with a combination of accuracy, precision, and resolution the world had never before seen. Today, Terra completes the fifth year in what was scheduled to be at least a 6-year mission to advance understanding of Earth’s climate system, and to help improve our quality of life.

Launched on December 18, 1999, Terra’s five onboard instruments began science operations in February 2000. Terra’s goal is to assess the health of the planet by providing comprehensive information about Earth’s land, oceans and atmosphere. From its vantage point 438 miles above our world, Terra orbits the Earth more than fourteen times a day and observes nearly the entire globe.


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High-resolution artist’s rendering of Terra satellite (1.5 MB; courtesy Reto Stockli, NASA Earth Observatory)


NPP Globe

Sending home roughly 1 million megabytes of data per day, Terra is helping scientists all over the world tackle important questions about the causes and effects of environmental changes. While the mission is still in the process of fulfilling its main science objectives, Terra’s portfolio of achievements to date already marks the mission a resounding success.

A key focus of the Terra mission is to help scientists measure the movements of carbon through Earth’s climate system. To meet their needs for industry, agriculture, and transportation, humans annually release more than 7 billion tons of carbon into the atmosphere through the burning of fossil fuel. Yet, scientists cannot account for where all this carbon ends up. Between 1 and 2 billion metric tons of carbon per year are “missing” from the global carbon budget.

Today Terra is providing scientists with some important clues to help them solve the mystery of the missing carbon. For example, every eight days the mission’s Moderate Resolution Imaging Spectroradiometer (MODIS) instrument produces a global map of where and how much carbon dioxide is drawn out of the air and fixed by vegetation during photosynthesis.

“These maps give scientists the best global measure ever made of the amount of carbon taken up by plants,” said Jon Ranson, Terra Project Scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “Carbon fixation by plants is the basis for capturing and storing the energy that fuels our world’s living systems and forms the foundation of the food web.”

  This false-color map represents the Earth’s carbon “metabolism” — the rate at which plants absorbed carbon out of the atmosphere. The map shows the global, annual average of the net productivity of vegetation on land and in the ocean during 2002. The yellow and red areas show the highest rates, ranging from 2 to 3 kilograms of carbon taken in per square meter per year. The green, blue, and purple shades show progressively lower productivity. (NASA image courtesy Reto Stockli, Earth Observatory) More information.

Tracking plant growth is also an important way in which Terra gives back to society. Scientists and resource managers are using Terra’s Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and MODIS instruments to monitor large agricultural regions and assess the health of croplands. These instruments produce maps of the “greenness” of the landscape, which scientists use as a measure of how much plant growth is occurring.

  The Terra ASTER instrument acquired these images over the U.S. Department of Agriculture’s Grazing Lands Research Laboratory near El Reno, Oklahoma, on Sept. 4, 2000. In the top image, bright red colors indicate green vegetation, which at this time of year only includes irrigated lands and riparian zones. Gray-green colors represent harvested winter wheat fields. Dendritic drainage patterns are clearly depicted in the lower left and upper right portions of the scene. ASTER’s three visible and near-infrared bands were used to make this image. The second panel shows the abundance of green vegetation (referred to as Normalized Difference Vegetation Index, or NDVI). NDVI is a measure of vegetation density and health. In this image, blue represents dense vegetation cover and yellow and red shows progressively less dense vegetation. (NASA images courtesy Andrew French, ASTER Science Team) More information.

Moreover, by comparing today’s Terra vegetation greenness maps to long-term averages, scientists can gauge when plants are under stress due to extreme heat or drought. The U.S. Department of Agriculture’s Foreign Agricultural Service uses Terra data to produce maps of drought across major food production regions in developing countries. In terms of lives lost and economic impact worldwide, drought is the costliest of natural disasters. Terra data are helping resource managers improve foreign market access for U.S. agricultural products, particularly during times of need.

  Drought has been looming over Kenya for several years, leaving many regions of the country parched and hungry. Now, as the 2004/2005 harvest draws to a close, the cereal deficit has grown to 300,000 metric tons, which means that up to 2.7 million people will need food aid this season-an unusually high number for Kenya. This map shows Normalized Difference Vegetation Index (NDVI) anomaly, recorded by the Terra MODIS instrument on February 3, 2005. The brown clusters in the Coast and Eastern provinces show patterns of dryness where vegetation is less dense than it has been in the past. More pronounced drought areas surround Central Province. Grey pixels indicate regions where data were not available. An arch of green through the center of the country reveals where there has been plentiful rainfall and the vegetation is thriving. (NASA image courtesy Jesse Allen, Earth Observatory) More information.