OCO-2/OCO-3

OCO-2 and OCO-3 are NASA’s Orbiting Carbon Observatories, which measure atmospheric carbon dioxide. OCO-2 launched 2 July 2014 into the A-train sun-synchronous orbit; OCO-3 was installed on the International Space Station in 2019, using the OCO-2 flight-spare spectrometer with a pointing mirror for target and snapshot maps. Both retrieve the column-averaged CO2 dry-air mole fraction, XCO2, to about 1 part per million from three near-infrared spectrometers reading reflected sunlight. They are atmospheric carbon sensors, not ocean instruments, but the data constrain the ocean carbon sink that absorbs roughly a quarter of human CO2 emissions.