The NASA Orbiting Carbon Observatory-2 (OCO-2) Mission: A Quick Look back at the First 3 Years of Operation

The NASA Orbiting Carbon Observatory-2 (OCO-2) was launched in July 2014 and was inserted at the head of the 705-km Afternoon Constellation (A-Train) a month later. Since early September of 2014, its 3-channel imaging grating spectrometer has returned over one million high-resolution spectra of reflected sunlight in the 0.765 microns (µm) molecular oxygen (O₂) A-Band and in the 1.61 and 2.06 µm carbon dioxide (CO₂) bands each day. Typically, between 25,000 and 75,000 of these soundings are sufficiently cloud-free to yield full-column estimates of the column-averaged CO₂ dry air mole fraction, X_CO2, with single sounding random errors near 0.5 ppm (0.125%) at solar zenith angles as large as 70 degrees. Another product derived from the OCO-2 spectra, solar induced chlorophyll fluorescence (SIF), is yielding additional insight into CO₂ uptake by the land biosphere. OCO-2 also returns estimates of surface pressure and the total column water vapor, which are sufficiently accurate to be of interest to the meteorological community. OCO-2 completed its nominal 2-year mission in October 2016, and began its first extended mission.

OCO-2 X_CO2 and SIF observations returned during its first 3 years in orbit provide a high-resolution global description of the atmospheric carbon cycle. They show the intense northern hemisphere spring drawdown associated with the land biosphere. They also show persistent X_CO2 anomalies over regions with intense fossil fuel combustion, such as Western Europe and the east coasts of China and North America. Areas with intense biomass burning, including central Africa, the Amazon, and Southeast Asia, also show anomalously high X_CO2 at some times of the year. Data collected between March 2015 and June of 2016 have provided a unique opportunity to study the carbon-climate feedbacks associated with the intense, 2015-2016 El Niño. Several teams have combined OCO-2 X_CO2 and SIF results with data from other spacecraft instruments, including Terra MOPITT, Aura OMI, and GOSAT TANSO-FTS to provide new insights into the relative roles of changes in ocean outgassing, drought, temperature stress, and fires in controlling the atmospheric CO₂ buildup during this event.

The precision and accuracy of the first, global, OCO-2 X_CO2 data product, Version 7 (V7), were validated through comparisons with X_CO2 estimates from the ground-based spectrometers in the Total Carbon Column Observing Network (TCCON) and other standards. After correcting known biases, the median difference between co-located OCO-2 and TCCON X_CO2 estimates is less than 0.4 ppm and the root-mean-square differences are typically less than 1.5 ppm. However, biases with amplitudes as large as 3 ppm are sometimes seen, particularly at high southern latitudes over the ocean during the southern winter. The primary sources of these and other biases have been traced to shortcomings in the instrument calibration, gas absorption coefficients and the retrieval algorithm. These issues have been corrected in the Version 8 (V8) processing system, which is now being used to reprocess the entire OCO-2 data record. This presentation will describe status of the OCO-2 mission, summarize recent results, and provide a preliminary overview of the performance of the V8 product.