ACOS

The ACOS (Atmospheric CO2 Observations from Space) Team, in collaboration with the Japan Aerospace Exploration Agency (JAXA), is participating in the analyses of GOSAT "IBUKI" observation data. The ACOS Team is formed by a number of institutions including the NASA Jet Propulsion Laboratory (JPL), the California Institute of Technology (Caltech), and Colorado State University, and is formed around the Orbiting Carbon Observatory (OCO) Science Team.

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. Through analyzing the GOSAT observational data, scientists will be able to ascertain the global distribution of carbon dioxide (CO2) and methane (CH4), and how the sources and sinks of these gases 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 retrievals of column-averaged CO2 in units of dry-air mole fraction (Xco2). The GOSAT team at JAXA produces GOSAT TANSO-FTS Level 1B (L1B) data products for internal use and for distribution to collaborative partners, such as ESA and NASA. These calibrated products are augmented by the ACOS Project 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 Team to radiances collected by GOSAT, will be applied as well to the spectra collected by the OCO-2 satellite. The latter is slated to replace OCO-1 which was lost at launch in February 2009. The launch of OCO-2 is planned for February 2013.

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