Solving the Carbon Conundrum
Progress Made on State-of-the-Art Carbon–Measuring Instrument
Scientists know the global levels of carbon dioxide in the atmosphere. They know how much is produced through natural processes and the burning of fossil fuels. But the numbers don’t jibe; the budget doesn’t balance. More carbon dioxide is produced than what shows up in the atmosphere. So where precisely does the carbon go and will the “sinks” that remove it from the environment continue doing so?
A state-of-the-art carbon-measuring instrument currently under development at Goddard promises to provide a more complete picture of the carbon issue and perhaps solve the conundrum, scientists believe.
A few of the CO2 Sounder Lidar team members are shown here inside a DC-8 during the 2010 field campaign demonstrating the instrument's capabilities. From top left (clockwise); Haris Riris, Jim Abshire, Bill Hasselbrack, and Mike Rodriguez.
Begun several years ago under Goddard research and development programs, the CO2 Sounder Lidar is a strong candidate for a next-generation carbon-monitoring mission, the Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS). Led by Principal Investigator Jim Abshire, the new measurement technique is proving in aircraft demonstrations that it can meet the ASCENDS criteria of providing global around-the-clock measurements with unprecedented precision and resolution, regardless of the season.
For scientists, the data couldn’t come too soon.
“We know the background levels of carbon dioxide very well. We have a global average,” said Randy Kawa, a Goddard atmospheric scientist involved in the sounder’s development. Scientists also know Earth’s oceans and vegetation remove and store carbon. “However, half of what we’re emitting isn’t showing up in the atmosphere,” Kawa added. “That’s why we need details of the processes. We need to know where the sinks are and how well they will operate in the future.” This is especially important since the carbon dioxide produced by coal-burning plants and vehicle emissions increases each year, he said.
Currently, a Japanese-built satellite, IBUKI or GOSAT (Greenhouse Gases Observing Satellite), is making global measurements of carbon dioxide. NASA, too, plans to launch its first-ever mission dedicated to carbon measurements in 2013. This mission, the Orbiting Carbon Observatory-2 (OCO-2), will fulfill the objectives of its predecessor, which was destroyed during a launch failure in 2009. NASA is planning to launch OCO-3 on the International Space Station after 2015.
CO2 Sounder Provides 24-hour Coverage
Although IBUKI and OCO were developed to characterize and map the locations of carbon sources and sinks and monitor how they change over time, neither one can provide around-the-clock coverage. That’s because they are equipped with “passive” instruments that rely on reflected sunlight to gather carbon measurements. The instruments, therefore, do not work at night, including high latitudes during winter, or on partially cloudy days.
In sharp contrast, the CO2 Sounder Lidar carries its own light source — a pair of tunable laser transmitters — and a two-wavelength laser-absorption spectrometer that measures both carbon dioxide and oxygen. Although laser light cannot penetrate thick clouds, it can measure through thin clouds and particles, which prove troublesome for passive systems.
“What we do is bounce a laser beam off Earth’s surface,” explained Abshire. Like all atmospheric gases, carbon dioxide and oxygen absorb the light in narrow wavelength bands. By tuning its lasers across those absorption lines, the instrument can determine the levels of both gases in that vertical path. “The more carbon-dioxide molecules in the path, the deeper the absorption lines,” Abshire said. Measuring oxygen is important, he added, because it reveals atmospheric pressure and helps scientists discern the mixing ratios of both gases.
Efforts also are afoot to develop a similar laser capability to measure methane, another greenhouse gas. Led by Goddard scientist Haris Riris, the addition would further enhance the sounder’s usefulness, said Bob Connerton, who oversees Earth science-related technology-development efforts at Goddard.
To demonstrate its viability as a space-based instrument, Abshire and his team began flying the sounder on high-altitude aircraft in 2008 — a field campaign supported by NASA’s Earth Science Instrument Incubator Program. These demonstration flights have occurred every summer since. In July, his team once again packaged the sounder inside a DC-8 and carried out seven separate flights collecting data over California, Nevada, British Columbia, Iowa, Minnesota, Wisconsin, and New Mexico.
“The sounder worked quite well,” Abshire said. “We recorded strong lidar signals and clear absorption lines for both carbon dioxide and oxygen at all altitudes and surface types. The instrument’s measurements clearly separated the laser signal scattered from the atmosphere and ground surface, as needed for a space mission.”
Though pleased with his instrument’s performance, he’s not declaring victory yet. NASA plans to compete the ASCENDS space instrument, and the Jet Propulsion Laboratory and the Langley Research Center are developing competing approaches. “Of course, I think our chances are very good because we have a really strong team. Our approach is also the most scalable to space and provides more information about carbon dioxide.”
Whether NASA will select his technique over the others remains to be seen. The Agency is expected to release an ASCENDS announcement of opportunity sometime in the next two years. “We’ll definitely be in competitive mode within a year,” but regardless of who ultimately wins, Abshire said, “we want this mission to occur.”
The Office of the Chief Technologist is involved in a variety of projects, missions, and technologies.