Dr. Sourish Basu is an expert in integrating multiple data streams – including satellite retrievals-in atmospheric inversions to estimate surface fluxes. He is a member of the OCO-2 Science Team, and is one of two main developers of the TM5 4DVAR DA system. For this project, he will perform two tasks, both of which are well within his expertise. In the first half of the project, Dr. Basu will conduct a series of OSSEs to determine the benefits of C-ESDRs in constraining CO2 fluxes vis-à-vis level-2 retrievals. This is especially important over data-poor regions of the world such as the tropics. Dr. Basu will iterate with other members of the team regarding the best OSSE experiments to perform. In the second half of the project, Dr. Basu will use the TM5 4DVAR system to produce flux estimates of CO2 from gap-filled and/or fused satellite data products for archival purposes. Flux estimates from fused products will be stringently evaluated to detect artifacts from instrument-dependent biases, and Dr. Basu will work with other members of the team to find ways to minimize their impact.