New NASA Spacecraft Dedicated to Studying Carbon Dioxide

An artist’s depiction of the orbiting carbon observatory, scheduled to launch February 23.

U.S., Japan launching observation satellites to monitor greenhouse gases

30 January 2009
By Cheryl Pellerin
Staff Writer

Washington — NASA’s Orbiting Carbon Observatory (OCO) will launch from Vandenberg Air Force Base in California on February 23, the first U.S. spacecraft dedicated to studying atmospheric carbon dioxide (CO₂), the greenhouse gas that is warming the planet and changing global climate.

The spacecraft will map the globe once every 16 days for at least two years. Atmospheric and carbon-cycle scientists will use that data to improve carbon-cycle models, reduce uncertainties in forecasts of how much carbon dioxide is in the atmosphere and make more accurate predictions of global climate change.

“While we understand approximately how much carbon dioxide is released into the atmosphere each year due to human influences,” Eric Ianson, NASA's OCO program executive for the Science Mission Directorate, said during a January 29 briefing, “we can only account for about half the carbon dioxide that doesn’t remain in the atmosphere.”

“This is the real carbon dioxide mystery,” David Crisp, OCO principal investigator at NASA's Jet Propulsion Laboratory in California, told America.gov.

Natural processes, he said, including those in oceans and land biomass like forests and plants, “are absorbing more than half of the CO₂ we dump into the atmosphere. OCO will show us not only how much of it goes into the ocean versus how much goes into land biomass, it will also tell us where” the CO₂ is going.

CO₂ absorbers are called sinks; CO₂ emitters, like processes that burn coal, natural gas and oil, are called sources.

OXYGEN-CARBON-OXYGEN

In the 10,000 years before the Industrial Revolution began in the mid-1700s, CO₂ levels rose less than 1 percent. Since then, CO₂ levels have risen 37 percent.

Before industrialization, the atmospheric concentration of CO₂ was 280 parts per million. By 2007, due almost entirely to human activity, it had risen to 383 parts per million.

Research by James Hansen of NASA’s Goddard Institute for Space Studies in New York and colleagues suggests that CO₂ in Earth’s atmosphere should be limited to 450 parts per million or less to avoid a dangerous tipping point. Over the last few decades, the number has been rising by about two parts per million per year.

After launch, OCO will be placed in a near-polar Earth orbit at an altitude of 705 kilometers (440 miles). Orbiting once every 98.8 minutes and repeating its orbit track every 16 days,  it will fly in a loose formation with other Earth-observing satellites of NASA’s Afternoon Constellation, called the A-Train — Aura, Parasol, Calipso, Cloudsat and Aqua.

The observatory’s science instrument consists of three parallel high-resolution spectrometers integrated into a single structure and fed by a common telescope.

OCO “will be making one of the most challenging measurements of atmospheric trace gas that has ever been made,” Charles Miller, OCO deputy principal investigator, said at the briefing. “To make the measurements of global carbon dioxide concentrations, we’ll be relying on the properties of individual carbon dioxide molecules and using the properties to do the remote sensing” of CO₂ from Earth’s surface to the top of the atmosphere.

A CO₂ molecule is composed of three atoms — oxygen-carbon-oxygen. Unique motions of atoms in the molecule act as molecular fingerprints.

“These molecules can absorb light at the infrared wavelengths and excite these vibrational motions,” Miller said. “We’re going to use that property of the molecules to detect carbon dioxide in the atmosphere.”

SOURCES AND SINKS

On January 23, the Japan Aerospace Exploration Agency launched its Greenhouse Gases Observing Satellite Ibuki, called GOSAT, designed to measure CO₂ and methane concentrations at 56,000 places in the Earth's atmosphere.

The OCO and GOSAT teams have been working together since 2004 to standardize the data each spacecraft produces and to validate their measurements against an absolute standard. Both observatories seek to measure CO₂ but have different objectives, Crisp said.

OCO’s primary mission is to measure CO₂ sinks, which tend to be dispersed, Crisp said, “and to do that I need much greater precision and more measurements than a mission like GOSAT that is primarily focused on measuring CO₂ sources,” which tend to be localized and intense.

GOSAT’s Fourier transform spectrometer measures a wider range of colors and can measure CO₂ and methane at the same times and places. GOSAT takes 56,000 measurements over three days; OCO takes 36,000 measurements over 100 minutes.

“Both the GOSAT team and our team are pushing two different measurement technologies to their absolute limits to make these measurements,” Crisp said.

Right now, he added, “everything we know about CO₂ in the Earth’s atmosphere has been learned from making measurements from about 100 surface stations distributed around the world. We’re going from that to 36,000 measurements every time we orbit Earth” — or about 8 million measurements every 16 days. (See “Volunteer Network Helps Track Global Greenhouse Gases.”)

“We know that carbon emissions are contributing to climate change and climate variability,” Anna Michalak, OCO science team manager at the University of Michigan, said at the briefing.

“What carbon cycle scientists want to understand is why plants and oceans are taking up as much carbon as they are and how this will change in the future,” she said. “The volume of data that OCO will provide is a huge stepping stone toward answering these questions.”