A NASA satellite launching later this month will measure the Earth's carbon dioxide levels in unprecedented detail, helping inform plans of attack against climate change.

Set to launch on February 23, the Orbiting Carbon Observatory will map the entire planet from 440 miles up, pinpointing where carbon dioxide is being emitted and where the greenhouse gas is being pulled from the air.

Identifying such sources and sinks will shed light on how carbon circulates from land to air to sea and back again — a process that remains poorly understood.

"We're extremely excited about OCO," said atmospheric chemist Charles Miller of NASA's Jet Propulsion Laboratory, which designed and operates the satellite. "We believe it will revolutionize our understanding of carbon cycling."

Over the last 250 years, atmospheric carbon dioxide levels have risen by about 40 percent, from 280 parts per million to more than 380. Climate scientists believe the increase in this heat-trapping gas is a chief driver of the planet's warming trend. Earth's average temperature has risen by 1.3 degrees Fahrenheit in the last 100 years.

But things could be much worse if it weren't for what are known as carbon sinks: Sixty percent of the carbon dioxide emitted by man has been absorbed out of the atmosphere. But scientists aren't sure where most of the sinks responsible are located, or what determines their efficiency over time.

"The fundamental focus of the OCO mission is the sinks," said project leader David Crisp, a physicist at JPL. "If we can't understand the processes controlling the buildup of CO2 in our atmosphere today, it will be impossible to make reliable predictions about how CO2 will affect climate in the future."

And sampling the entire planet from space is the best way to learn more, Crisp said. A system of 100 surface sensors scattered around the world makes very precise measurements of carbon dioxide, but the picture it paints is far from complete. And there are few of these stations in Africa, South America, and other parts of the Third World, meaning much of the planet is not being monitored.

"One hundred stations is just not enough," Crisp said. "I could put 100 stations in Iowa and not really have enough to say what's going on there."

OCO will measure atmospheric carbon dioxide using spectrometers — precision instruments that can distinguish 17,500 different colors over the spectrum of visible light. By analyzing the sunlight bouncing off of Earth, the satellite's spectrometers will identify the telltale wavelengths of light absorbed by carbon dioxide, revealing how much of it is in the air. The satellite will take 12 readings every second.

Finding sources and sinks is a significant technological challenge, Miller said. OCO will need to distinguish carbon dioxide levels differing by as little as 0.3 percent.

"This is the most difficult measurement of a trace gas ever attempted from space," Crisp said. "It's my team's job to prove that this really works."

Crisp's team will be able to check the accuracy of OCO's readings against the ground-based system, and with Japan's Greenhouse Gas Observing Satellite, or GOSAT, which beat OCO into space by a month. GOSAT is also using spectrometry to measure atmospheric CO2 and methane, another greenhouse gas. GOSAT will run for 5 years, sharing its data with NASA and other institutions. Crisp welcomes the opportunity to cooperate.

"About every six months, the two teams are going to get together, and we're going to compare notes and see how we're doing," he said.

OCO is a small spacecraft, measuring 7 feet tall by 3 feet across and weighing about 1000 pounds. Once aloft, it will join a constellation of five other scientific satellites called the A-Train, which gather data on clouds, aerosols, ozone, and other components of the atmosphere. The A-Train zips roughly from pole to pole, making a complete trip around the Earth in 100 minutes. The "A" stands for afternoon, because the spacecraft are all in a sun-synchronous orbit, which means it is always 1:30 p.m. on the ground beneath them, wherever they are.

OCO's total cost, from design and development to launch and operation, is $270 million. The spacecraft's mission has funding for two years, but if the telescope produces good data and money can be found, it may get an extension.__ __

See Also:

Image: NASA/JPL