Effects of atmospheric light scattering on spectroscopic observations of greenhouse gases from space. Part 2: Algorithm intercomparison in the GOSAT data processing for CO2 retrievals over TCCON sites

This report is the second in a series of companion papers describing the effects of\ud
atmospheric light scattering in observations of atmospheric carbon dioxide (CO2) by the\ud
Greenhouse gases Observing SATellite (GOSAT), in orbit since 23 January 2009. Here we\ud
summarize the retrievals from six previously published algorithms; retrieving columnaveraged\ud
dry air mole fractions of CO2 (XCO2) during 22 months of operation of GOSAT\ud
from June 2009. First, we compare data products from each algorithm with ground-based\ud
remote sensing observations by Total Carbon Column Observing Network (TCCON). Our\ud
GOSAT-TCCON coincidence criteria select satellite observations within a 5  radius of 11\ud
TCCON sites. We have compared the GOSAT-TCCON XCO2 regression slope, standard\ud
deviation, correlation and determination coefficients, and global and station-to-station\ud
biases. The best agreements with TCCON measurements were detected for NIES 02.xx and\ud
RemoTeC. Next, the impact of atmospheric light scattering on XCO2 retrievals was\ud
estimated for each data product using scan by scan retrievals of light path modification with\ud
the photon path length probability density function (PPDF) method. After a cloud pre-\ud
filtering test, approximately 25% of GOSAT soundings processed by NIES 02.xx, ACOS\ud
B2.9, and UoL-FP: 3G and 35% processed by RemoTeC were found to be contaminated by\ud
atmospheric light scattering. This study suggests that NIES 02.xx and ACOS B2.9\ud
algorithms tend to overestimate aerosol amounts over bright surfaces, resulting in an\ud
underestimation of XCO2 for GOSAT observations. Cross-comparison between algorithms\ud
shows that ACOS B2.9 agrees best with NIES 02.xx and UoL-FP: 3G while RemoTeC\ud
XCO2 retrievals are in a best agreement with NIES PPDF-D.GOSAT is a joint effort of the Japan Aerospace\ud
Exploration Agency (JAXA), the National Institute for Environmental\ud
Studies (NIES), and the Ministry of the Environment (MOE), Japan. Part of\ud
this work on ACOS B2.9 was performed at the Jet Propulsion Laboratory,\ud
California Institute of Technology, under contract with NASA. GOSAT\ud
spectra were kindly provided to the California Institute of Technology\ud
through a memorandum of understanding between JAXA and NASA. U.\ud
S. funding for TCCON is provided by NASA’s Terrestrial Ecology Program\ud
(grant number NNX11AG01G), the Orbiting Carbon Observatory Program,\ud
the Atmospheric CO2 Observations from Space (ACOS) Program, and the\ud
Department of Energy/Atmospheric Radiation Measurement (DOE/ARM)\ud
Program. The Darwin TCCON site was built at Caltech with funding from\ud
the OCO project and is operated by the University of Wollongong, with\ud
travel funds for maintenance and equipment costs funded by the OCO-2\ud
project. We acknowledge funding to support Darwin and Wollongong from\ud
the Australian Research Council, Projects LE0668470, DP0879468,\ud
DP110103118, and LP0562346. Lauder TCCON measurements are funded\ud
by New Zealand Foundation of Research Science and Technology contracts\ud
C01X0204 and CO1X0406. We acknowledge financial support of the Bia-\ud
łystok and Orléans TCCON sites from the Senate of Bremen and EU projects\ud
IMECC, GEOMON and InGOS as well as maintenance and logistical\ud
work provided by AeroMeteo Service (Białystok) and the RAMCES team at\ud
LSCE (Gif-sur-Yvette, France) and additional operational funding from the\ud
NIES GOSAT project. The Garmisch TCCON team acknowledges funding\ud
by the EC-INGOS project. Development of RemoTeC was partly funded by\ud
ESA through the GHG-CCI project (S. Guerlet) and by Deutsche Forschungsgemeinschaft\ud
(DFG) through grant BU2599/1-1 (A. Butz). The\ud
JRA-25/JCDAS data sets used for atmospheric transport modeling were\ud
provided by the cooperative, long-term reanalysis project by the Japan\ud
Meteorological Agency (JMA) and Central Research Institute of Electric\ud
Power Industry (CRIEPI). The authors thank Dr. Sasano, Director of the\ud
Center for Global Environmental Research at the NIES, the members of\ud
the NIES GOSAT and NASA ACOS projects.Peer-reviewedPublisher Versio