Orbiting Carbon Observatory-3 (OCO-3) - 12.12.18

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ISS Science for Everyone

Science Objectives for Everyone
The Orbiting Carbon Observatory-3 (OCO-3) is installed on the Japanese Experiment Module-Exposed Facility (JEM-EF) of the International Space Station (ISS) to observe the complex dynamics of the Earth’s atmospheric carbon cycle. The OCO-3 payload is designed to collect the space-based measurements needed to quantify variations in the column-averaged atmospheric carbon dioxide (CO2) dry-air mole fraction, XCO2, with the precision, resolution, and coverage needed to improve the understanding of surface CO2 sources and sinks (fluxes) on regional scales (≥1000 km), and the processes controlling their variability over the seasonal cycle.
Science Results for Everyone
Information Pending

The following content was provided by Annmarie Eldering, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details

OpNom: OCO-X

Principal Investigator(s)
Annmarie Eldering, Ph.D., NASA Jet Propulsion Laboratory, Pasadena, CA, United States

Information Pending

NASA Jet Propulsion Laboratory, Pasadena, CA, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
NASA - Science Mission Directorate (NASA-SMD)

Research Benefits
Earth Benefits, Scientific Discovery

ISS Expedition Duration
October 2018 - October 2019

Expeditions Assigned

Previous Missions
OCO-3 provides continuity in CO2 measurements following the OCO-2 prime mission, but will also provide unique science measurements from the ISS orbit. These unique measurements sampling during different periods of the diurnal cycle and capturing “flux snapshots” of large urban areas that would have taken OCO-2 several orbits to acquire.

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Experiment Description

Research Overview

  • The Orbiting Carbon Observatory-3 (OCO-3) continues the global carbon dioxide record started by OCO-2, but adds complementary information with sampling at all sunlit hours, a unique feature of sampling from the International Space Station (ISS). In addition to global sampling, OCO-3 capabilities allow for targeted local mapping of emissions hotspots. Megacities with massive carbon emissions are a potential target for measurements. Regional measurements in areas of high rates of carbon exchange that could be useful for process studies include snapshot maps over agricultural regions and forests, and mangroves.
  • Such focused measurements could be coordinated with field campaigns, and help bridge the large difference in scales of field studies and remote sensing. OCO-3:
    • Advances studies in carbon cycle science;
    • Builds on the capability of determining regional sources and sinks;
    • Retrieves XCO2 data over low latitudes;
    • Bridges the gap between the OCO-2 and ASCENDS (Active Sensing of CO2 Emissions over Nights, Days, and Seasons) missions;
    • Explores the detection limits and the value of resolving the diurnal cycle in chlorophyll fluorescence, and XCO2, to better constrain the carbon cycle flux in forests and plants;
    • Detects and quantifies the variability of XCO2 associated with human activities in rapidly developing urban centers.


The core of The Orbiting Carbon Observatory-3 (OCO-3) instrument, the optical bench assembly, assembled from OCO-2 instrument flight spares, is expected to have similar sensitivity and performance characteristics. However, OCO-2 uses an agile spacecraft to point the instrument, while OCO-3 utilizes an agile, 2-axis pointing mechanism to OCO-3 to take measurements from the International Space Station (ISS). This pointing mechanism, known as the pointing mirror assembly (PMA) is a new approach to provide the capability to look towards the bright reflection from the ocean, and provides new opportunities for mapping compact targets such as cities, power plants, or coastlines with 1 ppm precision in XCO2 measurements.
Deployed on the ISS, the different sampling characteristics from this low-inclination, non-sun synchronous orbit complements the sun synchronous, near-polar OCO-2 measurements and provides for new scientific investigations. The ISS orbit enables OCO-3 to sample across the full range of daylight hours, and emphasizes observations over the tropics, sub-tropics, and mid-latitudes, with periodic dense sampling at northern and southern mid-latitudes matching the orbit inclination.
The scientific contributions expected from OCO-3 are structured around 4 driving science questions that align with NASA’s Strategic Earth Science Goals:
  • What are the magnitudes, distribution, and variability of surface-atmosphere CO2 fluxes and their uncertainties over the relevant range of spatial and temporal scales?
  • What are the inter-annual, seasonal, and diurnal changes in uptake and release of CO2 on sub-regional and regional scales in the terrestrial biosphere?
  • How do the regional oceanic sources and sinks of atmospheric carbon dioxide change with sub-seasonal to inter-annual variability, e.g., synoptic forcing and El Nino/Southern Oscillation (ENSO)?
  • How is the growth in urban population and changing patterns of fossil fuel combustion influencing atmospheric CO2 distributions? Can regional trends of anthropogenic CO2 emissions be compared against the backdrop of natural variability?
Measurements from the global network of surface in situ stations provide excellent characterization of global atmospheric CO2 concentrations and trends, hemispheric gradients, and have driven major advances in fundamental carbon cycle science (Tans 2009, Keeling et al. 2011). However, the small number of sites, their sparse geographic distribution, and the measurement protocols limit the geospatial resolution and accuracy of inferred CO2 surface-atmosphere fluxes, even on an annual time scale. Remote sensing observations from the Japanese Greenhouse gases Observing SATellite (GOSAT) and OCO-2 mission substantially improve the spatial and temporal sampling from their mid-day orbits. OCO-3 further reduces the uncertainty of estimated CO2 fluxes by delivering an increased number of XCO2 measurements, with more frequent revisits, full sampling across the sunlit times of day. Its new pointing mechanism provides the ability to raster scan over localized source regions. Finally, flying the OCO-2 spare instrument on the ISS provides a sustained OCO instrument series data record. Simultaneous OCO-2 and OCO-3 observations can be used to increase the spatial and/or temporal resolution of the flux estimates, to length scales better matched with the fundamental carbon cycle processes.
OCO-3 also studies the role of the terrestrial biosphere: the most uncertain component of the global carbon cycle. In addition to making direct measurements of atmospheric CO2, both OCO-2 and the OCO-3 collect measurements of chlorophyll fluorescence. This provides a direct measure of photosynthetic activity, or gross primary production (GPP; CO2 taken up in photosynthesis), because chlorophyll fluorescence is a first-order by-product of photosynthesis. The OCO-3 instrument on ISS complements OCO-2 by sampling a large range of local sunlit times, seeing all sunlit hours over 20 to 50 days. These estimates of plant fluorescence and GPP during all sunlit hours are unprecedented in global carbon cycle observation, and provide additional constraints to reducing uncertainty in terrestrial carbon flux estimates.
Uncertainties in the sensitivity of the terrestrial biosphere to climate change also limit the skill with which coupled climate-carbon cycle models can forecast the future climate state and atmospheric CO2 levels (Friedlingstein et al. 2006; Huntingford et al. 2009). Determining whether continental regions are net carbon sources or sinks is of vital importance to understanding future acceleration or mitigation of atmospheric CO2 concentrations. Annually, however, plants absorb roughly as much CO2 through photosynthesis as they emit through respiration, and consequently the net ecosystem exchange (NEE) of CO2 between the land and atmosphere varies around zero. The uncertainties in GPP and ecosystem respiration (re: CO2 released back to the atmosphere from plant metabolism and dead plant material decay or combustion) must be well-constrained to know even the sign of NEE. The observations of fluorescence during all sunlit hours by OCO-3 substantially constrains these critical processes.
Additionally, in the coming decades, continued population growth and economic development is predicted to be concentrated in the developing world and lead to increased urban agglomeration (e.g, Cohen, 2004, and UN development reports) at sub-tropical latitudes. The largest urban areas (25 megacities) account for 75% of the global total fossil fuel CO2 emissions, and rapid growth (> 10% per year) is expected in developing regions over the coming 10 years. These developments can result in changes in the global patterns of fossil fuel combustion, both for primary power generation and in the transport sector. Timely estimates and verification of these changes are essential for accurate bottom-up estimates used to model inferences of natural net surface fluxes from top-down measurements of CO2. Furthermore, direct verification of trends in regional fossil fuel combustion aid evaluation of the socio-economic conditions prevalent at the outset of various future scenarios of CO2 emissions, and the atmospheric accumulation used to force climate model projections. With OCO-3’s “snapshot mode” of observations, there is the opportunity to explore mapping plumes from intense point sources of CO2 such as power stations, and urban centers.
In summary, two significant changes are implemented for OCO-3 over OCO-2 to enable measurements from the ISS: the addition of an agile, 2-axis pointing mechanism (PMA) and a polarization mechanism. These changes allow for the implementation of a new, more flexible observing strategy for OCO-3. OCO-3 provides a much higher density of sampling between 51°N and 51°S latitudes, as compared to OCO-2, and be able to collect nadir, glint, or snapshot mode observations on each orbit. These measurements are used to address key carbon cycle science questions, and OCO-3 on the ISS provides a key role in delivering sustained, global, scientifically-based, spaceborne measurements of atmospheric CO2 to monitor natural sources and sinks as part of NASAs proposed OCO-2/OCO-3/ASCENDS mission sequence and NASA’s Climate Architecture.

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Space Applications
OCO-3 demonstrates how space platforms can be used to study the Earth’s atmosphere and its effects on climate. Increasing demand for geospatial data means increasing use of spacecraft and space hardware for generating data.

Earth Applications
OCO-3 supports Earth applications by providing crucial climatic data, and preserving continuity of previously collected atmospheric records. OCO-3 investigates the benefit of solar-induced chlorophyll florescence as a product that would help agriculture managers detect plant stress earlier. In addition, understanding carbon sources and sinks can help in forecasting and reducing the long term risks of increased atmospheric heat retention.

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Operational Requirements and Protocols

OCO-3 is required to sample on the day side of the planet, and downlink data every orbit to prevent onboard buffering overflow. OCO-3 requires 1 uplink window per day. OCO-3 star tracker and pointing assembly must be pointed away from solar arrays and visiting vehicles. Commands and data are sent via the ISS network. Extravehicular Activities (EVAs) in the vicinity of the Japanese Experiment Module - Exposed Facility (JEM-EF) must result in powering off of the instrument.
OCO-3 is controlled by the mission operations team at Jet Propulsion Laboratory (JPL) from the ground. Operations are autonomous in nature, and do not require any crew time. In the event of a low-power event on ISS, EVA near JEM-EF, or visiting vehicle arrival/departure, OCO-3 shall suspend operations to protect ISS, astronauts, and the instrument.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

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Related Websites

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