GHG Session 1

The Greenhouse gases Observing SATellite (GOSAT) has operated for about six years since its launch on January 23, 2009. During the past six years, all of the GOSAT standard data products were opened to general users, and many of the data products went through several updates. From the spectral data that GOSAT collected, the concentrations of major greenhouse gases (GHGs), namely carbon dioxide (CO₂) and methane (CH₄), were retrieved at NIES (released as GOSAT Level 2 data product), and their precisions (excluding biases) are now about 0.5% and 0.7%, respectively. Other groups in the research community, SRON/ KIT, University of Leicester, University of Bremen, and US OCO-2 team also retrieved the column GHGs from GOSAT TANSO-FTS Level 1B spectral data. Using GOSAT Level 2 data product, the monthly surface fluxes of CO₂ and CH₄, on sub-continental and ocean-basin scales, were estimated. The flux estimates for the first three years of GOSAT operation (2009 – 2012) are now available. The Level 2 column concentration data were also utilized to monitor GHGs’ temporal and spatial changes.

In 2014, GOSAT went through some technical difficulties in the functioning of its solar paddle and sensor pointing mechanism, and the characteristics of the Fourier transform spectrometer onboard were therefore altered to some degree. The influence of this alteration on the retrieved concentrations has been detected.

In this presentation, we will summarize the six-year-long GHG observation by GOSAT and present the global distributions and variations of the GHG concentrations and the surface flux estimates. We will also explain the changes in the characteristics of the GOSAT data products after June 2014 owing to the influence of the technical difficulties.

NASA’s Orbiting Carbon Observatory-2 (OCO-2) was successfully launched from Vandenberg Air Force Base in California on 2 July 2014.  After completing a series of spacecraft check-out activities and orbit raising maneuvers, OCO-2 joined the 705 km Afternoon Constellation (A-Train) on August 6, 2014.  Its 3-channel imaging grating spectrometer was then cooled to its operating temperatures and a series of calibration and validation activities was initiated.  This instrument’s rapid sampling, small (< 3 km²) sounding footprint, and high sensitivity, combined with an optimized observing strategy, are expected to provide improved coverage of the ocean, partially cloudy regions, and high latitude continents than earlier missions.

In early October, OCO-2 started routinely collecting almost one million soundings over the sunlit hemisphere each day.  Around 25% of these soundings (250,000/day) are sufficiently cloud free to yield full column estimates of X_CO2.  For routine science operations, the instrument’s bore sight is pointed to the local nadir or at the “glint spot,” where sunlight is specularly reflected from the Earth’s surface. Nadir observations provide the best spatial resolution and yield more cloud-free X_CO2 soundings over land. Glint observations have much more signal over dark, ocean surfaces, yielding much more complete coverage of the globe. The initial observation sequence alternates between glint and nadir observations on consecutive 16-day ground-track repeat cycles, so that the entire sunlit hemisphere is sampled in both modes at 32-day intervals. This observation sequence is currently being optimized to yield more complete coverage of the globe. OCO-2 can also target selected surface calibration and validation sites to collect thousands of soundings as the spacecraft flies overhead.  The primary surface targets include well calibrated surface sites, such as Railroad Valley, Nevada, and Total Carbon Column Observing Network (TCCON) stations, which make precise measurements of CO₂ and other trace gases from the ground. 

The OCO-2 team started delivering calibrated, geo-located, spectra to the NASA Goddard Earth Sciences Data and Information Services Center (GES-DISC) on 30 December, 2014.  Deliveries of Level 2 products, including estimates of X_CO2, surface pressure, and solar-induces chlorophyll fluorescence (SIF) are scheduled to begin before March 30, 2015.  This presentation will describe the OCO-2 mission status, early products, and near-term plans.  It will also provide a preview of the kinds of information that will be provided by future greenhouse gas monitoring missions, such as the proposed ESA CarbonSat mission, which are expected to provide estimates of X_CH4 as well as X_CO2 and SIF, with far greater coverage than OCO-2.