Measurements of carbon dioxide and solar-induced chlorophyll fluorescence from the NASA Orbiting Carbon Observatories 2 and 3 and the Geostationary Carbon Observatory
Abstract
In September of 2014, NASA's Orbiting Carbon Observatory-2 (OCO-2) started returning about 5.5 million soundings each month that were sufficiently cloud free to retrieve estimates of the column-averaged carbon dioxide (CO$ _{2}$) dry air mole fraction, XCO$ _{2}$, with single sounding precisions of $\sim$~0.125% (0.5 ppm out of the 400 ppm CO$ _{2}$ background) and accuracies of $\sim$~0.2% on regional scales. This timing provided a unique opportunity to observe the carbon cycle response to changes in the tropical climate associated with the record-setting 2015-2016 El Niño. Estimates of the XCO$_{2}$ retrieved from OCO-2 measurements clearly resolved reductions in tropical ocean outgassing early in this event. OCO-2 XCO$_{2}$ estimates were then combined with observations of solar induced chlorophyll fluorescence (SIF) to document reductions in uptake and increases in the release of CO$_{2}$ by tropical forests associated with drought, temperature stress, and fires. More recent observations provided an opportunity to document the recovery of the tropical carbon cycle to its normal, non-El Niño state. That never happened. OCO-2 XCO$_{2}$ and SIF estimates indicate that tropical forests, once thought to be significant net sinks of CO$_{2}$, are now persistent net sources. A longer data record is critical for diagnosing the processes responsible for this apparent change and its implications for the carbon cycle response to climate change. On smaller scales, OCO-2 XCO$_{2}$ and SIF estimates have been used to quantify CO$_{2}$ emissions from large urban areas and individual power plants. While these measurements clearly demonstrate the potential of space-based XCO$_{2}$ and SIF measurements for monitoring localized sources, the narrow OCO-2 measurement swath does cross most such sites frequently enough to track their emission trends. Fortunately, in May 2019, OCO-2 was joined by its sister mission, the Orbiting Carbon Observatory-3 (OCO-3), which was installed on the International Space Station (ISS). While OCO-2 collects global XCO$_{2}$ and SIF observations from a 1:30 PM near-polar orbit, OCO-3 collects these observations from dawn to dusk from the low-inclination (51$^\circ$-degree), ISS orbit. OCO-3 also includes a fast, 2-axis pointing mechanism enabling Snapshot Area Maps (SAMs) of XCO$_{2}$ and SIF over targets as large as 80 km x 80 km. By combining OCO-2 and OCO-3 observations, we expect to gain a better understanding of both diurnal variations in CO$_{2}$ fluxes and urban emissions. In 2023, NASA plans to launch the Earth Ventures Geostationary Carbon Observatory, GeoCarb. The GeoCarb instrument will be deployed on a commercial communications satellite that will stationed over 85 $\pm$ 20$^\circ$ W longitude to observe North and South America. GeoCarb's imaging grating spectrometer builds on the heritage of OCO-2 and OCO-3 to obtain high-spatial-resolution maps of column-averaged CO$_{2}$, methane (CH$_{4}$) and carbon monoxide (CO) as well as SIF over this domain. This presentation will summarize recent results from OCO-2 and OCO-3 and provide an update on the status of the implementation of GeoCarb. It will also outline the potential for synergistic observations from these low Earth orbit and geostationary platforms and their implications for a future space-based global carbon monitoring system.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E..15C