NASA’s OCO-2: Measuring the Earth’s Carbon Dioxide Sources from Space

NASA researchers look forward to getting their first results from OCO-2, a satellite that will study Earth’s carbon dioxide sources and sinks and their contributions to climate change from space.

After Orbiting Carbon Observatory (OCO)’s launch vehicle failure in 2009, NASA researchers, who have been working on this project for the past 13 years, finally launched its successor, OCO-2, into orbit on July 2, 2014.

“OCO-2 was designed to do one thing and one thing only, hopefully really well: measure atmospheric CO₂ from space better than has ever [been] done,” said Dr. Ross Salawitch, professor in the Department of Atmospheric & Oceanic Science and the Department of Chemistry and Biochemistry at the University of Maryland.

In August the OCO-2 satellite will join the Afternoon Constellation, or A-train, a group of satellites that orbits the earth 99 times per day in a sun synchronous, polar orbit.

“OCO-2 is a very punctual gal: she reports for duty at 1:30 p.m. local solar time each and every orbit,” said Salawitch, who also works for the NASA Jet Propulsion Laboratory in Pasadena, California, and is a member of ESSIC.

How OCO-2 records CO₂ measurements, Salawitch said, is not hard to understand.

 “OCO-2 records sunlight that traverses the atmosphere, hits the surface, and is reflected back through the atmosphere to the spacecraft,” said Salawitch. “The sunlight that reaches the spacecraft contains fingerprints that allow scientists to infer the abundance of atmospheric CO₂.”

“In other words, for sunlight of a very specific color (or wavelength), CO₂ blocks this sunlight from reaching the spacecraft,” stated Salawitch.

OCO-2 obtains observations of CO₂ column abundance from around world, said Salawitch. NASA has designed an orbit for OCO-2 with a 16-day repeat cycle, in which the same ground track is visited every 16 days.  On the other 15 days, OCO-2 will observe nearby regions, in a steady progression of the orbit path.

“Since the measurement concept is based on measurements of reflected sunlight, our measurements of atmospheric CO₂ are restricted to clear sky conditions,” said Salawitch. “The science team has designed computer software to sort through the data and assess which observations were obtained in cloud free or nearly cloud free conditions.”

Dr. David Crisp, a senior research scientist in the Jet Propulsion Laboratory at California Institute of Technology, said the idea for the OCO and OCO-2 projects spurred from his consideration of the use of remote sensing and reflective sunlight to examine the Earth’s greenhouse gases.

“On a whim, I thought ‘what would happen if I looked at reflective sunlight?’” and it actually worked, said Crisp, who has worked on this project since OCO’s inception in 2000.

According to Crisp, the Science Team is looking for explanations as to how sources and sinks of CO₂ work, and which natural processes are currently absorbing over half of the CO₂ emitted into the atmosphere each year.

“Some natural process that has not been identified is cleaning up half of our mess. Currently there are no plans for any change in fossil inputs that will reduce our output, but some natural process is taking care of it for free,” said Crisp. “We don’t know where, and we don’t know for how long it will keep doing so.”

The project has collaborators that expand the entire globe, including some in Canada, New Zealand, China, the Netherlands, France, England and Australia. While other satellites have measured CO₂ with other atmospheric gases, OCO-2 is the first of its kind to be “optimized for precise measurement of atmospheric CO₂.”

Randy Pollock, NASA’s lead instrument systems engineer, said that during the past few weeks his main role has consisted of performing basic tests of the instrument to verify that the satellite’s systems are functioning properly.

Pollock stated that by Monday, August 4, the satellite’s optics will begin to cool.  By Wednesday of that week, the satellite will be close to optimal operating temperatures for accurate data collection.

“We have to evaluate all [the measurements] as best as we can in space so that we can tell the science team what to focus on,” said Pollock. “There are some small adjustments we’ll have to make just because you can’t simulate space perfectly on the ground.”

“I was one of the people to operate the original project back in 2001, so I’ve been 13 years on this job,” added Pollock. “It’s going to be an exciting mission to finally see in space after all these years.”

OCO-2 has a planned funding for two years’ time, said Salawitch, but the design of the spacecraft and instrument allow for much longer operations: 10 years or longer.  NASA will review the mission as the 2-year anniversary approaches and make a decision about extending the mission.

The processed data will be archived and made available to scientists thought the world at the Goddard Space Flight Center in Greenbelt, Maryland.