NASA's Orbiting Carbon Observatory-3 (OCO-3) is getting a bright start to the new year. Since December, the agency's newest carbon dioxide (CO2) monitoring mission has collected more than 20 million measurements of sunlight reflected off Earth's surface, or radiance. This light data lies at the heart of the mission's ability to measure atmospheric CO2, a major contributor to climate change. The public release of the data began on January 30, 2020.
Here's why it matters.
OCO-3's primary instrument is a highly accurate, three-channel spectrometer. When sunlight moves through the atmosphere to Earth's surface and is reflected back to the spacecraft, the instrument splits the incoming light into a spectrum of colors — much like a light shone through a prism creates a rainbow.
Each of those colors corresponds to a different frequency and wavelength of light. Because different gasses in the atmosphere absorb only specific colors (or frequencies), and do so in their own way, each has a unique absorption "fingerprint." OCO-3's spectrometer detects and count these fingerprints for both CO2 and oxygen.
"Measuring the number of oxygen molecules lets us determine the ratio of CO2 molecules to air molecules," said Annmarie Eldering, OCO-3 project scientist. "When we talk about a CO2 concentration like 400 parts per million, it is that ratio."
They then run the radiance (light) data against a fine-tuned model of the atmosphere that takes into account variables like water vapor and the sun's location relative to the ground at a given time which can influence the results.
"We filter out the poor-quality data, where it might just be too cloudy or where the Sun may have been too low on the horizon, too dim for us to learn anything useful," Eldering said. "If the data and the radiance model don't match, we make adjustments to find the very best explanation for our observed light."
Thus, the radiance data is the foundation on which OCO-3's CO2 measurements are based. The mission team produced several maps to demonstrate what the data looks like, including images over Buenos Aires and San Jose, California (see images above/or wherever we're putting them). The data from darker, less reflective areas is shown in dark purple. The brightest areas are shown in white.
OCO-3, which launched to the International Space Station in May 2019, is tasked with continuing the CO2 record of its still-operational predecessor OCO-2; however, there are some distinct differences between the two missions. The OCO-2 spacecraft was launched into a near-polar orbit, which means that every time is passes over a given point on Earth's surface, it does so at the same time of day. The space station, on the other hand, makes about 16 orbits of Earth per day, each shifting slightly to the west on its longitudinal axis. This orbit, combined with the fact that Earth itself is also rotating, allows OCO-3 to measure CO2 over the same areas at different times of day.
OCO-3 also has a new pointing mechanism that can capture "snapshot maps" — detailed mini-maps of CO2 over specific areas of interest like cities and volcanoes. The mechanism can map areas of 50 by 50 miles (80 by 80 kilometers) in just two minutes. In order for the mechanism to work, though, it has to know what time and over what location it is flying. While the space station's variable orbit makes this a challenge as well, it's not one too great for the OCO-3 mission team.
"The teamwork, the complicated process and collaborations required, all of that has worked really well and has really been a success," Eldering said.
OCO-3 is on track to produce its much-anticipated CO2 maps, including hotspot maps over various cities, this April.
For more information on OCO-3, visit:
To access the newly released radiance data, visit: