Immediately after the loss of the Orbiting Carbon Observatory (OCO) mission, the GOSAT Project Team in Japan invited the NASA OCO team to contribute to the GOSAT TANSO-FTS data analysis. To exploit this opportunity, NASA reconstituted the OCO team as the Atmospheric CO2 Observations from Space (ACOS) Task.
GOSAT (Greenhouse gases Observing SATellite) is a spacecraft dedicated to measurements of concentrations of carbon dioxide and methane, the two major greenhouse gases, from space. The spacecraft was launched successfully on January 23, 2009, and has been operating properly since then. GOSAT is a partnership between Japanese Aerospace Exploration Agency (JAXA), the Ministry of the Environment (MoE) in Japan, and the National Institute for Environmental Sciences (NIES), Japan. JAXA delivers radiances acquired by the TANSO-FTS sensor to the Jet Propulsion Laboratory (JPL), where they are processed using the OCO/ACOS algorithms.
The ACOS Task was formed by a number of institutions including the NASA Jet Propulsion Laboratory (JPL), the California Institute of Technology (Caltech), and Colorado State University. The ACOS task was terminated in September of 2012, while resetting the OCO-2 Team in preparation for the OCO-2 mission launch in 2014. The ACOS Version 3.3 data is released by the OCO-2 Team in June 2013.
Through analyzing the GOSAT observational data, scientists will be able to ascertain the global distribution of carbon dioxide (CO2) , and how the sources and sinks vary with seasons, years, and locations.
At present, only one ACOS product is publicly available - ACOS_L2S. It is a Level-2 product that contains full physics retrievals of column-averaged CO2 in units of dry-air mole fraction (Xco2). The TANSO-FTS calibrated radiance products are augmented by the ACOS algorithms with additional geolocation information and further corrections. The resulting ACOS Level 1B product (with calibrated radiances and geolocation) is the input to the ACOS Level-2 production process. The distribution of GOSAT and ACOS L1B products is currently restricted by cooperation agreements between JAXA and NASA.
The Level-2 Xco2 retrieval, applied by the ACOS Task to radiances collected by TANSO-FTS, will be applied as well to the spectra collected by the OCO-2 satellite.
Note that the CO2 concentrations in the ACOS_L2S product are retrieved using the Short Wave InfraRed (SWIR) bands only, 1.56-1.72 µm and 1.92-2.08 µm. That also means data are from the sun-lit portion of the orbit only, which is the descending node of GOSAT. The local sun time at equator crossing is around 12:45 – 13:15 PM.
For more details on the satellite geometry and the retrievals, Users are strongly encouraged to familiarize with the README document below. Help on very particular issues of physics of retrievals is available from the ACOS Team