Records of Fused and Assimilated Satellite Carbon Dioxide Observations and Fluxes from Multiple Instruments

Principal Investigator (PI): Vineet Yadav, NASA's Jet Propulsion Laboratory

Numerous existing sensors measure concentrations of carbon dioxide (CO₂) in the atmosphere. Many of these sensors, such as Orbiting Carbon Observatory-2 (OCO-2), the Greenhouse Gases Observing Satellite (GOSAT), and Atmospheric Infrared Sounder (AIRS), provide global scale observations, but these observations are oversampled in some locations and under sampled in others. By contrast, contiguous, global fields fused from multiple instruments would be useful to the scientific community.

The team is creating fused and/or gap-filled Earth System Data Records (ESDRs) of CO₂ concentrations by integrating observations from the Atmospheric CO₂ Observations from Space (ACOS) retrievals from GOSAT, OCO-2, and AIRS. Furthermore, we also are creating gap-filled OCO-2 and ACOS-GOSAT products. We designate all these ESDRs to be Level 3 products, as they are being derived from non gap-filled, bias-corrected, Level 2 retrievals.

We will perform rigorous validation of these ESDRs by:

1. Comparing them against in-situ and aircraft observations,
2. Comparing regional fluxes and uncertainties obtained by utilizing Level 2 satellite retrievals within two data assimilation systems, against the fluxes obtained by using gap-filled and/or fused ESDRs, and
3. Identifying spatio-temporal similarity and “dissimilarity” between flux maps obtained by using Level 2 retrievals and gap-filled or fused ESDRs.

What we are doing is novel both with respect to science and technology in that multiple XCO₂ (the ratio of the total dry-air column of CO₂ to that of dry air) and complementary three-dimensional fields (e.g., averaging kernels) from multiple instruments are being used to create a single fused product, and a full error covariance (not just standard errors) in compressed form is being provided as part of Level 3 products (no NASA Level 3 product has ever provided this information for any field in the past).

Algorithms being used to build the ESDRs were developed “in-house” under the aegis of NASA’s AIST program. Moreover the project utilizes the capabilities built through NASA’s Carbon Monitoring System (CMS) program for CO₂ flux estimation to validate the proposed Level 3 products.