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A team of Colorado State University atmospheric scientists is at the center of NASA’s next Earth orbiting science mission, which will map variations of carbon dioxide across the globe.
On Tuesday, February 24, NASA’s Jet Propulsion Laboratory is scheduled to launch the Orbiting Carbon Observatory, known as OCO, from California’s Vandenberg Air Force Base to measure reflected sunlight in color bands absorbed by carbon dioxide and oxygen. The Colorado State team will be part of an international team responsible for turning those observations into precise measurements of carbon dioxide concentration and ultimately determining sources of the greenhouse gas as well as "sinks" or places where the gas is being absorbed.
Denis O’Brien, senior research scientist at Colorado State, leads an international team responsible for developing the algorithm or computer program that will convert the spectroscopic measurements to atmospheric CO2 data.
"We have a pretty good idea of what’s happening to carbon dioxide in the atmosphere, but we don’t know the mechanisms," said O’Brien, who, with Graeme Stephens, University Distinguished Professor at Colorado State, worked on early concepts for OCO. "We’re going to take the CO2 measurements and derive sources and sinks accounting for winds, local weather, etc."
The measurements are critical because 50 to 60 percent of the planet’s carbon dioxide is currently being absorbed into oceans and incorporated into land plants and soils. With OCO, scientists will learn more about where that’s happening, how it works, and whether the phenomenon will continue.
The mission is essentially tracking the Earth’s "breathing," said Scott Denning, atmospheric science professor at Colorado State.
"The issue is half of the CO2 from fossil fuels doesn’t stay in the air," Denning said. "We’re trying to follow tiny changes in CO2 as it moves over the world to find out whether the planet will keep doing what it’s doing. We essentially have automatic 50 percent emissions reductions, provided for free by the oceans and land. That’s about $400 billion per year worth of carbon based on the current market price of $100 per ton of carbon."
Denning, O’Brien and Stephens are part of a team of nine scientists at Colorado State – in the Department of Atmospheric Science and at the Cooperative Institute for Research in the Atmosphere or CIRA – on the science team for OCO, which is led by JPL’s David Crisp. Other key scientists on the project at Colorado State are Chris O’Dell, research scientist, and David Baker, postdoctoral fellow.
Industry partners in OCO include the Orbital Sciences Corp. and Hamilton Sundstrand Sensor Systems.
How the satellite works, according to Randy Pollock, Instrument Systems Engineer and Calibration Lead on the mission for NASA’s Jet Propulsion Laboratory: "The instrument measures sunlight that has passed through the atmosphere twice: once on the way down to the surface and then again on the way up to the orbiting spacecraft. As it does so, certain colors are absorbed by the CO2 that the sunlight encounters along the way. The instrument splits these colors into something like a rainbow, but covering only a tiny range of colors outside the range of human vision. The differences in how the CO2 molecules absorb different colors of light creates a pattern that looks almost like a barcode with shades of gray rather than blacks and whites. From the subtle variations in the grays we can tell how many molecules of carbon dioxide the sunlight saw as it passed through the atmosphere.
"We also make an independent measure of oxygen. By taking the two together, we can determine the ratio of carbon dioxide to oxygen because oxygen exists almost perfectly uniformly everywhere on the planet. That tells us the ratio of CO2 in the air."
OCO grew out of early discussions on CloudSat, another NASA Earth orbiting satellite that measures precipitation in clouds, said Stephens, who served as the principal investigator on the CloudSat mission. CloudSat, which was designed by Stephens and JPL, launched 438 miles above Earth on April 28, 2006, and is giving scientists around the world unprecedented data about fresh water produced by clouds.
Much like the OCO mission, Colorado State scientists at CIRA are responsible for collecting measurements from CloudSat and converting them into useful data for the scientific community. NASA has honored Colorado State with prestigious awards for its contributions to the success of the CloudSat mission, which is part of NASA’s A-Train of Earth observation satellites.
"We are a unique institution as far as carbon measurements are concerned," Stephens said of Colorado State. "We’re analyzing this problem from end-to-end, from eking out the carbon dioxide information in the colors of reflected sunlight to estimating forest growth while at the same time raising the next generation of carbon cycle scientists."
OCO will help researchers more accurately predict carbon dioxide sinks that have been created by such activities as forest fire suppression and abandonment of farms to woodlots in the developed world, Denning said.
"Plants on land convert CO2 to wood, leaves, and roots during photosynthesis, but the carbon comes right back out as CO2 when the plants die and decay," Denning said. "The fact that land plants currently take up nearly 25 percent of the world’s fossil fuel emissions means that at the planetary scale, plants are growing faster than they are dying, which is quite remarkable. Many scientists expect theses carbon sinks to saturate and stop taking up carbon in the coming years. We have to understand how the sinks work so we can anticipate when the climate might start changing much faster than it’s already changing, and OCO is going to let us do that."